Date   

Re: Store preset converters/transverters as a separate definition?

klaus.hutschenreuther@...
 

And without saving?

If delta = 0Hz then it’s „easy“ to switch off mid beacon lock.

Then Disturbing the beacon don‘t matter.

 

Herzliche Grüße

Klaus Hutschenreuther

 

 

 

Von: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> Im Auftrag von Siegfried Jackstien
Gesendet: Freitag, 25. Juni 2021 23:19
An: main@SDR-Radio.groups.io
Betreff: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

no that can not be done (but would be nice)

set offset for lnb to 9.75ghz ... click on beacon signal ... offset is shows as (example -3000Hz) and offset is then stored as 9749.997.000

that would be nice but that is an option simon had to add to save that as the new converter definition

i tried out what my lnb needs on day and over the night .. max drift between hot and cold is around 1 kc ... so i made a list with 100hz steps and 1.5 kc wide (a few safety steps above and below) ...

if outside temp changes (say it starts raining) i just select a new entry out of my list and i try to be below 100 hz on the beacon

you sure know that there is a "damned idiot" who disturbs sometimes the mid beacon ... with an offset below 100hz i (just in case) switch off beacon lock and do manual tune (rit) ... so i can live without a gps reference for the lnb :-)

ok i have to switch off beacon lock if that guy disturbs the beacon ... but it is stable enough to still work fine with only the tcxo stability

saving the new calculated offset as new converter definition sure would be a nice add on ... no idea if simon can add it

greetz sigi dg9bfc

Am 25.06.2021 um 21:57 schrieb klaus.hutschenreuther@...:

Hi Simon, hi Siggi

 

·       Can the SDRConsole calculate the current offset itself and save it with a "click of a button" if required?

·       Add or subtract the current delta, for example + 246Hz or -450Hz (see menu „Geostationary Satellite Becon“)

to the saved (old) offset and save it as a new offset?

 

Herzliche Grüße

Klaus Hutschenreuther

 

 

 

Von: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> Im Auftrag von Siegfried Jackstien
Gesendet: Freitag, 25. Juni 2021 21:22
An: main@SDR-Radio.groups.io
Betreff: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

would be nice if we could change converter offset without the need to stop the radio

that would be superb if you have a "drifting" converter (like an lnb outside in the sun)

i now stop radio ... select new offset (i made a longer list in 100hz steps) and restart the radio

only a drop down list (say if you hover the mouse to top line of the rx box) to select from and radio is still running would be much faster

greetz sigi dg9bfc

Am 23.06.2021 um 13:51 schrieb jdow:

And allow a list of identities to choose from as read from configuration storage (registry or AppData or wherever).

{^_^}


On 20210623 03:48:01, Siegfried Jackstien wrote:

could that be solved with the identities??

save one setup as user 1 and other setup as user2??

just thinking

dg9bfc sigi

Am 23.06.2021 um 07:02 schrieb Simon Brown:

Hi,

 

A definition would not contain any hardware-specific settings. Maybe you need multiple defns for the same device which is not currently supported.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Max
Sent: 22 June 2021 18:50
To:
main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

Hi Simon

Many thanks for coming back. Please also see my post in "Requests" on the main forum  re: also storing "PA enable" state for the HL2 along with the definition. Maybe that's another issue?

Max


--

- + - + -

Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.

 


Re: Store preset converters/transverters as a separate definition?

Siegfried Jackstien
 

no that can not be done (but would be nice)

set offset for lnb to 9.75ghz ... click on beacon signal ... offset is shows as (example -3000Hz) and offset is then stored as 9749.997.000

that would be nice but that is an option simon had to add to save that as the new converter definition

i tried out what my lnb needs on day and over the night .. max drift between hot and cold is around 1 kc ... so i made a list with 100hz steps and 1.5 kc wide (a few safety steps above and below) ...

if outside temp changes (say it starts raining) i just select a new entry out of my list and i try to be below 100 hz on the beacon

you sure know that there is a "damned idiot" who disturbs sometimes the mid beacon ... with an offset below 100hz i (just in case) switch off beacon lock and do manual tune (rit) ... so i can live without a gps reference for the lnb :-)

ok i have to switch off beacon lock if that guy disturbs the beacon ... but it is stable enough to still work fine with only the tcxo stability

saving the new calculated offset as new converter definition sure would be a nice add on ... no idea if simon can add it

greetz sigi dg9bfc

Am 25.06.2021 um 21:57 schrieb klaus.hutschenreuther@...:

Hi Simon, hi Siggi

 

  • Can the SDRConsole calculate the current offset itself and save it with a "click of a button" if required?
  • Add or subtract the current delta, for example + 246Hz or -450Hz (see menu „Geostationary Satellite Becon“)

to the saved (old) offset and save it as a new offset?

 

Herzliche Grüße

Klaus Hutschenreuther

 

 

 

Von: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> Im Auftrag von Siegfried Jackstien
Gesendet: Freitag, 25. Juni 2021 21:22
An: main@SDR-Radio.groups.io
Betreff: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

would be nice if we could change converter offset without the need to stop the radio

that would be superb if you have a "drifting" converter (like an lnb outside in the sun)

i now stop radio ... select new offset (i made a longer list in 100hz steps) and restart the radio

only a drop down list (say if you hover the mouse to top line of the rx box) to select from and radio is still running would be much faster

greetz sigi dg9bfc

Am 23.06.2021 um 13:51 schrieb jdow:

And allow a list of identities to choose from as read from configuration storage (registry or AppData or wherever).

{^_^}

On 20210623 03:48:01, Siegfried Jackstien wrote:

could that be solved with the identities??

save one setup as user 1 and other setup as user2??

just thinking

dg9bfc sigi

Am 23.06.2021 um 07:02 schrieb Simon Brown:

Hi,

 

A definition would not contain any hardware-specific settings. Maybe you need multiple defns for the same device which is not currently supported.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Max
Sent: 22 June 2021 18:50
To:
main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

Hi Simon

Many thanks for coming back. Please also see my post in "Requests" on the main forum  re: also storing "PA enable" state for the HL2 along with the definition. Maybe that's another issue?

Max


--

- + - + -

Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.

 


Re: Store preset converters/transverters as a separate definition?

klaus.hutschenreuther@...
 

Hi Simon, hi Siggi

 

  • Can the SDRConsole calculate the current offset itself and save it with a "click of a button" if required?
  • Add or subtract the current delta, for example + 246Hz or -450Hz (see menu „Geostationary Satellite Becon“)

to the saved (old) offset and save it as a new offset?

 

Herzliche Grüße

Klaus Hutschenreuther

 

 

 

Von: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> Im Auftrag von Siegfried Jackstien
Gesendet: Freitag, 25. Juni 2021 21:22
An: main@SDR-Radio.groups.io
Betreff: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

would be nice if we could change converter offset without the need to stop the radio

that would be superb if you have a "drifting" converter (like an lnb outside in the sun)

i now stop radio ... select new offset (i made a longer list in 100hz steps) and restart the radio

only a drop down list (say if you hover the mouse to top line of the rx box) to select from and radio is still running would be much faster

greetz sigi dg9bfc

Am 23.06.2021 um 13:51 schrieb jdow:

And allow a list of identities to choose from as read from configuration storage (registry or AppData or wherever).

{^_^}

On 20210623 03:48:01, Siegfried Jackstien wrote:

could that be solved with the identities??

save one setup as user 1 and other setup as user2??

just thinking

dg9bfc sigi

Am 23.06.2021 um 07:02 schrieb Simon Brown:

Hi,

 

A definition would not contain any hardware-specific settings. Maybe you need multiple defns for the same device which is not currently supported.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Max
Sent: 22 June 2021 18:50
To:
main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

Hi Simon

Many thanks for coming back. Please also see my post in "Requests" on the main forum  re: also storing "PA enable" state for the HL2 along with the definition. Maybe that's another issue?

Max


--

- + - + -

Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.

 


Re: Store preset converters/transverters as a separate definition?

Siegfried Jackstien
 

would be nice if we could change converter offset without the need to stop the radio

that would be superb if you have a "drifting" converter (like an lnb outside in the sun)

i now stop radio ... select new offset (i made a longer list in 100hz steps) and restart the radio

only a drop down list (say if you hover the mouse to top line of the rx box) to select from and radio is still running would be much faster

greetz sigi dg9bfc

Am 23.06.2021 um 13:51 schrieb jdow:

And allow a list of identities to choose from as read from configuration storage (registry or AppData or wherever).

{^_^}

On 20210623 03:48:01, Siegfried Jackstien wrote:

could that be solved with the identities??

save one setup as user 1 and other setup as user2??

just thinking

dg9bfc sigi

Am 23.06.2021 um 07:02 schrieb Simon Brown:

Hi,

 

A definition would not contain any hardware-specific settings. Maybe you need multiple defns for the same device which is not currently supported.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Max
Sent: 22 June 2021 18:50
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Store preset converters/transverters as a separate definition?

 

Hi Simon

Many thanks for coming back. Please also see my post in "Requests" on the main forum  re: also storing "PA enable" state for the HL2 along with the definition. Maybe that's another issue?

Max


--
- + - + -
Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.


Re: SDR-Console Power dBm Accuracy

Tony_AD0VC
 

Wherever you worked, they were lucky to have you. 

Tony
AD0VC


From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of jdow <jdow@...>
Sent: Thursday, June 24, 2021 9:20 PM
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] SDR-Console Power dBm Accuracy
 
(I plead too many years misspent as an electronics engineer in various aspects of RF communications.)

{^_-}

On 20210624 18:22:01, Larry Dodd wrote:
Jdow
Whoa!  I’ll have to print that out and study it over a couple days. 
Thanks!
Larry, K4LED 

On Jun 24, 2021, at 8:25 PM, jdow <jdow@...> wrote:

 OK, so if it is down around 5 dB you don't really care if it is 4 or 6 unless your location is preternaturally quiet. 10 dB might be rather high. But, it might have the "feature" of overriding external noise sources to flatten out variations in external noise. It is also very easy to build a 1 dB noise figure reasonably high dynamic range amplifier in that frequency range. I'd limit the upper end to about 25 MHz to 26 MHz with a reasonably sharp LPF so that children's band ops don't get you. And in the 28 MHz to 29.7 MHz region you may have various ham radio transmitters bother you from time to time.

The low frequency makes some of the job easy, which is always nice.

So let's talk setup, You want a nice RF relay configuration as that can be basic to your whole operation. You also want a nice temperature regulated coax termination with a small diameter double shielded coax feeder no more than a foot long on one leg of the switch. The other leg goes to your hot source when calibrating the noise figure and to the antenna when measuring the sky. For the relay I'd use a pair of "T" configuration diodes. You'd want to be able to turn on the two diodes on top of the T and off the stalk of the T for "on" condition and reverse it for off. You'd want to drive the diodes hard enough they are low impedance. And keep the two T's as identical as possible. Join them at one end of the top of the Ts. The other end of each T goes to noise source resistor and the other to hot source or antenna. Once you have this working with less than 1dB loss for the ON position and 40 dB or more for the off position we can move on to the rest of the design.

You need a driver for the relay. Since it's semi-conductor based it can be simple. But, let's make it a little complex, such as an Arduino, Raspberry PI, or similar. You can drive each switch independently with GPIO pins from the little CPU module. Make sure the little computer you select has a sound card input and a programming interface you can deal with. (BASIC or Python or similar would be nice.)

Hook this up for noise figure measurement simply because it's an easy way to start. And hook up audio out of SDRC or SDRSharp or whatever. Set the SDR to SSB or CW reception and select a suitable bandwidth, probably 1kHz is a good compromise.

Build a little test program. Teach it to accept batches of audio samples at about an 8 ksps rate, square each sample. Each squared sample is multiplied by a small number on the order of 0.001 for starters. Multiply a sum value by 0.999, actually 1 minus your small number. Then add your multiplied sample to the sum. This provides a bit if averaging. You probably want averaging with MUCH smaller numbers. But that requires some cheating, later. You should be able to read this sum periodically and observe your average "power" reading. (Yeah yeah - no R for it to be a real power. But we work with power ratios so R cancels out. I LOVE it when incidental terms cancel out that way. {^_-}) If you use floats or 16 bit integers then 1/2^10 is a reasonable division factor. If you use 32 bit integers or have the luxury of doubles rather than floats then 1/2^20 can save an extra loop.

If you are using 16 bits or floats then every time you get 2^10 samples into your average feed that value to a second averager using the same 2^10 factor. The idea is to end up with about a 2 minute power average.

In a second little test program teach the relay to switch from source A to source B on command and check performance. Once that works teach it to switch once a minute forever until YOU tell it to stop. Develop a 100 ms timer triggered by the source switch providing a software output value. Call it 0 when the timer is triggered and 1 when the timer is not triggered.

Then you can put this together almost cut and paste. You should have available from these pieces code to average audio samples, a once per second transition from low to high or high to low, and triggered by each switch a 100 ms "let it all settle" signal.

Build TWO audio averagers, the audio input software, and the switch driver with its timers into a single module. In software "switch" the audio from the input to one audio sum over to the other. Let's say your switch has a value of 0 when it is on the 290K source and 1 when it is connected to the external source. When both the switch signal and the 100ms delay signal are 0 feed audio through to the reference summing input. When the switch signal is 1 and the delay signal is 0 feed the audio into the external source sum. When the delay signal is 1 feed the input audio to the infinite bit bucket - do nothing when the receiver might be unstable. (This is easier than trying to make the switch deliver no transients.)

Then after this has all had a half hour or two to really settle down you should have two reasonably precise (1% or less variance with time) values you can measure. They are both "powers" so you can take their ratio in DB and do your mathematical magic on them. The very low noise of the proposed amplifier preserves accuracy even though you do not know precise values for the noise figure aka noise temperature calculations. It's the same ratio you want for your radio astronomy source.

I hope that was almost clear enough to implement. I was totally riffing on it.

{^_^}   Joanne

On 20210624 16:19:23, Larry Dodd wrote:
The frequency spectrum of interest here are 15 to 30 MHz HF. As far as noise figures go we would like to see 10 or better. 
Larry, K4LED 


On Jun 24, 2021, at 7:15 PM, jdow <jdow@...> wrote:

 It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED





Re: SDR-Console Power dBm Accuracy

Larry Dodd
 

Jdow,
Your experience is obvious.
Thanks for sharing. 
Larry

On Jun 24, 2021, at 11:21 PM, jdow <jdow@...> wrote:

 (I plead too many years misspent as an electronics engineer in various aspects of RF communications.)

{^_-}

On 20210624 18:22:01, Larry Dodd wrote:
Jdow
Whoa!  I’ll have to print that out and study it over a couple days. 
Thanks!
Larry, K4LED 

On Jun 24, 2021, at 8:25 PM, jdow <jdow@...> wrote:

 OK, so if it is down around 5 dB you don't really care if it is 4 or 6 unless your location is preternaturally quiet. 10 dB might be rather high. But, it might have the "feature" of overriding external noise sources to flatten out variations in external noise. It is also very easy to build a 1 dB noise figure reasonably high dynamic range amplifier in that frequency range. I'd limit the upper end to about 25 MHz to 26 MHz with a reasonably sharp LPF so that children's band ops don't get you. And in the 28 MHz to 29.7 MHz region you may have various ham radio transmitters bother you from time to time.

The low frequency makes some of the job easy, which is always nice.

So let's talk setup, You want a nice RF relay configuration as that can be basic to your whole operation. You also want a nice temperature regulated coax termination with a small diameter double shielded coax feeder no more than a foot long on one leg of the switch. The other leg goes to your hot source when calibrating the noise figure and to the antenna when measuring the sky. For the relay I'd use a pair of "T" configuration diodes. You'd want to be able to turn on the two diodes on top of the T and off the stalk of the T for "on" condition and reverse it for off. You'd want to drive the diodes hard enough they are low impedance. And keep the two T's as identical as possible. Join them at one end of the top of the Ts. The other end of each T goes to noise source resistor and the other to hot source or antenna. Once you have this working with less than 1dB loss for the ON position and 40 dB or more for the off position we can move on to the rest of the design.

You need a driver for the relay. Since it's semi-conductor based it can be simple. But, let's make it a little complex, such as an Arduino, Raspberry PI, or similar. You can drive each switch independently with GPIO pins from the little CPU module. Make sure the little computer you select has a sound card input and a programming interface you can deal with. (BASIC or Python or similar would be nice.)

Hook this up for noise figure measurement simply because it's an easy way to start. And hook up audio out of SDRC or SDRSharp or whatever. Set the SDR to SSB or CW reception and select a suitable bandwidth, probably 1kHz is a good compromise.

Build a little test program. Teach it to accept batches of audio samples at about an 8 ksps rate, square each sample. Each squared sample is multiplied by a small number on the order of 0.001 for starters. Multiply a sum value by 0.999, actually 1 minus your small number. Then add your multiplied sample to the sum. This provides a bit if averaging. You probably want averaging with MUCH smaller numbers. But that requires some cheating, later. You should be able to read this sum periodically and observe your average "power" reading. (Yeah yeah - no R for it to be a real power. But we work with power ratios so R cancels out. I LOVE it when incidental terms cancel out that way. {^_-}) If you use floats or 16 bit integers then 1/2^10 is a reasonable division factor. If you use 32 bit integers or have the luxury of doubles rather than floats then 1/2^20 can save an extra loop.

If you are using 16 bits or floats then every time you get 2^10 samples into your average feed that value to a second averager using the same 2^10 factor. The idea is to end up with about a 2 minute power average.

In a second little test program teach the relay to switch from source A to source B on command and check performance. Once that works teach it to switch once a minute forever until YOU tell it to stop. Develop a 100 ms timer triggered by the source switch providing a software output value. Call it 0 when the timer is triggered and 1 when the timer is not triggered.

Then you can put this together almost cut and paste. You should have available from these pieces code to average audio samples, a once per second transition from low to high or high to low, and triggered by each switch a 100 ms "let it all settle" signal.

Build TWO audio averagers, the audio input software, and the switch driver with its timers into a single module. In software "switch" the audio from the input to one audio sum over to the other. Let's say your switch has a value of 0 when it is on the 290K source and 1 when it is connected to the external source. When both the switch signal and the 100ms delay signal are 0 feed audio through to the reference summing input. When the switch signal is 1 and the delay signal is 0 feed the audio into the external source sum. When the delay signal is 1 feed the input audio to the infinite bit bucket - do nothing when the receiver might be unstable. (This is easier than trying to make the switch deliver no transients.)

Then after this has all had a half hour or two to really settle down you should have two reasonably precise (1% or less variance with time) values you can measure. They are both "powers" so you can take their ratio in DB and do your mathematical magic on them. The very low noise of the proposed amplifier preserves accuracy even though you do not know precise values for the noise figure aka noise temperature calculations. It's the same ratio you want for your radio astronomy source.

I hope that was almost clear enough to implement. I was totally riffing on it.

{^_^}   Joanne

On 20210624 16:19:23, Larry Dodd wrote:
The frequency spectrum of interest here are 15 to 30 MHz HF. As far as noise figures go we would like to see 10 or better. 
Larry, K4LED 


On Jun 24, 2021, at 7:15 PM, jdow <jdow@...> wrote:

 It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED





Re: SDR-Console Power dBm Accuracy

jdow
 

(I plead too many years misspent as an electronics engineer in various aspects of RF communications.)

{^_-}

On 20210624 18:22:01, Larry Dodd wrote:
Jdow
Whoa!  I’ll have to print that out and study it over a couple days. 
Thanks!
Larry, K4LED 

On Jun 24, 2021, at 8:25 PM, jdow <jdow@...> wrote:

 OK, so if it is down around 5 dB you don't really care if it is 4 or 6 unless your location is preternaturally quiet. 10 dB might be rather high. But, it might have the "feature" of overriding external noise sources to flatten out variations in external noise. It is also very easy to build a 1 dB noise figure reasonably high dynamic range amplifier in that frequency range. I'd limit the upper end to about 25 MHz to 26 MHz with a reasonably sharp LPF so that children's band ops don't get you. And in the 28 MHz to 29.7 MHz region you may have various ham radio transmitters bother you from time to time.

The low frequency makes some of the job easy, which is always nice.

So let's talk setup, You want a nice RF relay configuration as that can be basic to your whole operation. You also want a nice temperature regulated coax termination with a small diameter double shielded coax feeder no more than a foot long on one leg of the switch. The other leg goes to your hot source when calibrating the noise figure and to the antenna when measuring the sky. For the relay I'd use a pair of "T" configuration diodes. You'd want to be able to turn on the two diodes on top of the T and off the stalk of the T for "on" condition and reverse it for off. You'd want to drive the diodes hard enough they are low impedance. And keep the two T's as identical as possible. Join them at one end of the top of the Ts. The other end of each T goes to noise source resistor and the other to hot source or antenna. Once you have this working with less than 1dB loss for the ON position and 40 dB or more for the off position we can move on to the rest of the design.

You need a driver for the relay. Since it's semi-conductor based it can be simple. But, let's make it a little complex, such as an Arduino, Raspberry PI, or similar. You can drive each switch independently with GPIO pins from the little CPU module. Make sure the little computer you select has a sound card input and a programming interface you can deal with. (BASIC or Python or similar would be nice.)

Hook this up for noise figure measurement simply because it's an easy way to start. And hook up audio out of SDRC or SDRSharp or whatever. Set the SDR to SSB or CW reception and select a suitable bandwidth, probably 1kHz is a good compromise.

Build a little test program. Teach it to accept batches of audio samples at about an 8 ksps rate, square each sample. Each squared sample is multiplied by a small number on the order of 0.001 for starters. Multiply a sum value by 0.999, actually 1 minus your small number. Then add your multiplied sample to the sum. This provides a bit if averaging. You probably want averaging with MUCH smaller numbers. But that requires some cheating, later. You should be able to read this sum periodically and observe your average "power" reading. (Yeah yeah - no R for it to be a real power. But we work with power ratios so R cancels out. I LOVE it when incidental terms cancel out that way. {^_-}) If you use floats or 16 bit integers then 1/2^10 is a reasonable division factor. If you use 32 bit integers or have the luxury of doubles rather than floats then 1/2^20 can save an extra loop.

If you are using 16 bits or floats then every time you get 2^10 samples into your average feed that value to a second averager using the same 2^10 factor. The idea is to end up with about a 2 minute power average.

In a second little test program teach the relay to switch from source A to source B on command and check performance. Once that works teach it to switch once a minute forever until YOU tell it to stop. Develop a 100 ms timer triggered by the source switch providing a software output value. Call it 0 when the timer is triggered and 1 when the timer is not triggered.

Then you can put this together almost cut and paste. You should have available from these pieces code to average audio samples, a once per second transition from low to high or high to low, and triggered by each switch a 100 ms "let it all settle" signal.

Build TWO audio averagers, the audio input software, and the switch driver with its timers into a single module. In software "switch" the audio from the input to one audio sum over to the other. Let's say your switch has a value of 0 when it is on the 290K source and 1 when it is connected to the external source. When both the switch signal and the 100ms delay signal are 0 feed audio through to the reference summing input. When the switch signal is 1 and the delay signal is 0 feed the audio into the external source sum. When the delay signal is 1 feed the input audio to the infinite bit bucket - do nothing when the receiver might be unstable. (This is easier than trying to make the switch deliver no transients.)

Then after this has all had a half hour or two to really settle down you should have two reasonably precise (1% or less variance with time) values you can measure. They are both "powers" so you can take their ratio in DB and do your mathematical magic on them. The very low noise of the proposed amplifier preserves accuracy even though you do not know precise values for the noise figure aka noise temperature calculations. It's the same ratio you want for your radio astronomy source.

I hope that was almost clear enough to implement. I was totally riffing on it.

{^_^}   Joanne

On 20210624 16:19:23, Larry Dodd wrote:
The frequency spectrum of interest here are 15 to 30 MHz HF. As far as noise figures go we would like to see 10 or better. 
Larry, K4LED 


On Jun 24, 2021, at 7:15 PM, jdow <jdow@...> wrote:

 It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED





Re: SDR-Console Power dBm Accuracy

Larry Dodd
 

Jdow
Whoa!  I’ll have to print that out and study it over a couple days. 
Thanks!
Larry, K4LED 

On Jun 24, 2021, at 8:25 PM, jdow <jdow@...> wrote:

 OK, so if it is down around 5 dB you don't really care if it is 4 or 6 unless your location is preternaturally quiet. 10 dB might be rather high. But, it might have the "feature" of overriding external noise sources to flatten out variations in external noise. It is also very easy to build a 1 dB noise figure reasonably high dynamic range amplifier in that frequency range. I'd limit the upper end to about 25 MHz to 26 MHz with a reasonably sharp LPF so that children's band ops don't get you. And in the 28 MHz to 29.7 MHz region you may have various ham radio transmitters bother you from time to time.

The low frequency makes some of the job easy, which is always nice.

So let's talk setup, You want a nice RF relay configuration as that can be basic to your whole operation. You also want a nice temperature regulated coax termination with a small diameter double shielded coax feeder no more than a foot long on one leg of the switch. The other leg goes to your hot source when calibrating the noise figure and to the antenna when measuring the sky. For the relay I'd use a pair of "T" configuration diodes. You'd want to be able to turn on the two diodes on top of the T and off the stalk of the T for "on" condition and reverse it for off. You'd want to drive the diodes hard enough they are low impedance. And keep the two T's as identical as possible. Join them at one end of the top of the Ts. The other end of each T goes to noise source resistor and the other to hot source or antenna. Once you have this working with less than 1dB loss for the ON position and 40 dB or more for the off position we can move on to the rest of the design.

You need a driver for the relay. Since it's semi-conductor based it can be simple. But, let's make it a little complex, such as an Arduino, Raspberry PI, or similar. You can drive each switch independently with GPIO pins from the little CPU module. Make sure the little computer you select has a sound card input and a programming interface you can deal with. (BASIC or Python or similar would be nice.)

Hook this up for noise figure measurement simply because it's an easy way to start. And hook up audio out of SDRC or SDRSharp or whatever. Set the SDR to SSB or CW reception and select a suitable bandwidth, probably 1kHz is a good compromise.

Build a little test program. Teach it to accept batches of audio samples at about an 8 ksps rate, square each sample. Each squared sample is multiplied by a small number on the order of 0.001 for starters. Multiply a sum value by 0.999, actually 1 minus your small number. Then add your multiplied sample to the sum. This provides a bit if averaging. You probably want averaging with MUCH smaller numbers. But that requires some cheating, later. You should be able to read this sum periodically and observe your average "power" reading. (Yeah yeah - no R for it to be a real power. But we work with power ratios so R cancels out. I LOVE it when incidental terms cancel out that way. {^_-}) If you use floats or 16 bit integers then 1/2^10 is a reasonable division factor. If you use 32 bit integers or have the luxury of doubles rather than floats then 1/2^20 can save an extra loop.

If you are using 16 bits or floats then every time you get 2^10 samples into your average feed that value to a second averager using the same 2^10 factor. The idea is to end up with about a 2 minute power average.

In a second little test program teach the relay to switch from source A to source B on command and check performance. Once that works teach it to switch once a minute forever until YOU tell it to stop. Develop a 100 ms timer triggered by the source switch providing a software output value. Call it 0 when the timer is triggered and 1 when the timer is not triggered.

Then you can put this together almost cut and paste. You should have available from these pieces code to average audio samples, a once per second transition from low to high or high to low, and triggered by each switch a 100 ms "let it all settle" signal.

Build TWO audio averagers, the audio input software, and the switch driver with its timers into a single module. In software "switch" the audio from the input to one audio sum over to the other. Let's say your switch has a value of 0 when it is on the 290K source and 1 when it is connected to the external source. When both the switch signal and the 100ms delay signal are 0 feed audio through to the reference summing input. When the switch signal is 1 and the delay signal is 0 feed the audio into the external source sum. When the delay signal is 1 feed the input audio to the infinite bit bucket - do nothing when the receiver might be unstable. (This is easier than trying to make the switch deliver no transients.)

Then after this has all had a half hour or two to really settle down you should have two reasonably precise (1% or less variance with time) values you can measure. They are both "powers" so you can take their ratio in DB and do your mathematical magic on them. The very low noise of the proposed amplifier preserves accuracy even though you do not know precise values for the noise figure aka noise temperature calculations. It's the same ratio you want for your radio astronomy source.

I hope that was almost clear enough to implement. I was totally riffing on it.

{^_^}   Joanne

On 20210624 16:19:23, Larry Dodd wrote:
The frequency spectrum of interest here are 15 to 30 MHz HF. As far as noise figures go we would like to see 10 or better. 
Larry, K4LED 


On Jun 24, 2021, at 7:15 PM, jdow <jdow@...> wrote:

 It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED




Re: SDR-Console Power dBm Accuracy

jdow
 

I'd worry a little there unless you never encounter any 10 meter amateur repeaters. There are a few around the country. It probably is not a problem. But watch for it just the same. High signals could suppress all signals in the analog portion and cause overload in the A/D portion of the design I proposed.

It's a fun problem. And I sort of like the design I proposed. It occurs to me that it could be modified for three audio sums so you could get continuous NF and astronomy measurements on a 3 second rotation.

{^_^}

On 20210624 16:21:48, Larry Dodd wrote:
For a single frequency we use 29MHz. 
Larry, K4LED 

On Jun 24, 2021, at 7:06 PM, jdow <jdow@...> wrote:

 What frequency are you using?
{^_^}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED




Re: SDR-Console Power dBm Accuracy

jdow
 

OK, so if it is down around 5 dB you don't really care if it is 4 or 6 unless your location is preternaturally quiet. 10 dB might be rather high. But, it might have the "feature" of overriding external noise sources to flatten out variations in external noise. It is also very easy to build a 1 dB noise figure reasonably high dynamic range amplifier in that frequency range. I'd limit the upper end to about 25 MHz to 26 MHz with a reasonably sharp LPF so that children's band ops don't get you. And in the 28 MHz to 29.7 MHz region you may have various ham radio transmitters bother you from time to time.

The low frequency makes some of the job easy, which is always nice.

So let's talk setup, You want a nice RF relay configuration as that can be basic to your whole operation. You also want a nice temperature regulated coax termination with a small diameter double shielded coax feeder no more than a foot long on one leg of the switch. The other leg goes to your hot source when calibrating the noise figure and to the antenna when measuring the sky. For the relay I'd use a pair of "T" configuration diodes. You'd want to be able to turn on the two diodes on top of the T and off the stalk of the T for "on" condition and reverse it for off. You'd want to drive the diodes hard enough they are low impedance. And keep the two T's as identical as possible. Join them at one end of the top of the Ts. The other end of each T goes to noise source resistor and the other to hot source or antenna. Once you have this working with less than 1dB loss for the ON position and 40 dB or more for the off position we can move on to the rest of the design.

You need a driver for the relay. Since it's semi-conductor based it can be simple. But, let's make it a little complex, such as an Arduino, Raspberry PI, or similar. You can drive each switch independently with GPIO pins from the little CPU module. Make sure the little computer you select has a sound card input and a programming interface you can deal with. (BASIC or Python or similar would be nice.)

Hook this up for noise figure measurement simply because it's an easy way to start. And hook up audio out of SDRC or SDRSharp or whatever. Set the SDR to SSB or CW reception and select a suitable bandwidth, probably 1kHz is a good compromise.

Build a little test program. Teach it to accept batches of audio samples at about an 8 ksps rate, square each sample. Each squared sample is multiplied by a small number on the order of 0.001 for starters. Multiply a sum value by 0.999, actually 1 minus your small number. Then add your multiplied sample to the sum. This provides a bit if averaging. You probably want averaging with MUCH smaller numbers. But that requires some cheating, later. You should be able to read this sum periodically and observe your average "power" reading. (Yeah yeah - no R for it to be a real power. But we work with power ratios so R cancels out. I LOVE it when incidental terms cancel out that way. {^_-}) If you use floats or 16 bit integers then 1/2^10 is a reasonable division factor. If you use 32 bit integers or have the luxury of doubles rather than floats then 1/2^20 can save an extra loop.

If you are using 16 bits or floats then every time you get 2^10 samples into your average feed that value to a second averager using the same 2^10 factor. The idea is to end up with about a 2 minute power average.

In a second little test program teach the relay to switch from source A to source B on command and check performance. Once that works teach it to switch once a minute forever until YOU tell it to stop. Develop a 100 ms timer triggered by the source switch providing a software output value. Call it 0 when the timer is triggered and 1 when the timer is not triggered.

Then you can put this together almost cut and paste. You should have available from these pieces code to average audio samples, a once per second transition from low to high or high to low, and triggered by each switch a 100 ms "let it all settle" signal.

Build TWO audio averagers, the audio input software, and the switch driver with its timers into a single module. In software "switch" the audio from the input to one audio sum over to the other. Let's say your switch has a value of 0 when it is on the 290K source and 1 when it is connected to the external source. When both the switch signal and the 100ms delay signal are 0 feed audio through to the reference summing input. When the switch signal is 1 and the delay signal is 0 feed the audio into the external source sum. When the delay signal is 1 feed the input audio to the infinite bit bucket - do nothing when the receiver might be unstable. (This is easier than trying to make the switch deliver no transients.)

Then after this has all had a half hour or two to really settle down you should have two reasonably precise (1% or less variance with time) values you can measure. They are both "powers" so you can take their ratio in DB and do your mathematical magic on them. The very low noise of the proposed amplifier preserves accuracy even though you do not know precise values for the noise figure aka noise temperature calculations. It's the same ratio you want for your radio astronomy source.

I hope that was almost clear enough to implement. I was totally riffing on it.

{^_^}   Joanne

On 20210624 16:19:23, Larry Dodd wrote:
The frequency spectrum of interest here are 15 to 30 MHz HF. As far as noise figures go we would like to see 10 or better. 
Larry, K4LED 


On Jun 24, 2021, at 7:15 PM, jdow <jdow@...> wrote:

 It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED




Re: SDR-Console Power dBm Accuracy

Larry Dodd
 

For a single frequency we use 29MHz. 
Larry, K4LED 

On Jun 24, 2021, at 7:06 PM, jdow <jdow@...> wrote:

 What frequency are you using?
{^_^}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED



Re: SDR-Console Power dBm Accuracy

Larry Dodd
 

The frequency spectrum of interest here are 15 to 30 MHz HF. As far as noise figures go we would like to see 10 or better. 
Larry, K4LED 


On Jun 24, 2021, at 7:15 PM, jdow <jdow@...> wrote:

 It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED



Re: SDR-Console Power dBm Accuracy

jdow
 

It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED



Re: SDR-Console Power dBm Accuracy

jdow
 

This is why the more usual configuration involves a connector swap or a coaxial switch and two noise sources at known noise temperatures. You mention attenuators. That means the 290K noise source temperature doesn't matter much. What matters is the attenuator temperature. (It gets messy, doesn't it?)

{^_^}

On 20210624 12:56:35, Bob Dengler wrote:
At 6/24/2021 04:15 AM, you wrote:
Bob
Thanks. The brand new BBGen noise source is mounted in an rf tight metal box that is peltier temperature controlled at 72 degrees F. Have a brand new JFW 110 dB step attenuator mounted in that same box. No surplus stuff. 
Larry, K4LEDÂ 
The BBGen itself has a VSWR spec of 2:1 on & 10:1 off.  Probably a lossy open when off, it's going to need at least 15 dB of attenuation to make it look close to 50 ohms when off.  But 15 dB of attenuation will leave barely enough ENR to be usable.  I think you'd be better off with a surplus commercial noise source.

Bob NO6B 







Re: SDR-Console Power dBm Accuracy

jdow
 

What frequency are you using?
{^_^}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED



Re: SDR-Console Power dBm Accuracy

jdow
 

Ah, Tempest - it can leak like a sieve but that leakage must not be related to what is going on inside the box in any detectable manner. A common technique is to simply try to make the leakage undetectable. I am not sure which approach is best. I've vacillated between the two approaches over the years. Ah memories!

{^_-}   Joanne

On 20210624 08:02:18, Larry Dodd wrote:
Gedas,
I’ll check your video out. Thanks. Actually have been deriving MDS from NF knowing the bandwidth. Interesting. You mentioned tempest. I was a cryptographer and maintained tempest equipment in a long past life. Ha! What an interesting place SDR-Radio is. 
Thanks,
73
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED



Re: SDR-Console Power dBm Accuracy

jdow
 

This approach is "workable" but it is not as accurate because there are more sources of error in the measurement. The Y-Factor approach simply requires a pair of noise sources each at a well calibrated temperature roughly in line with the expected noise figure you will be measuring.

The MDS method depends on precision of the measurement noise bandwidth. The Y-factor approach does not. The Y-factor approach requires two easily measured temperatures. an RF relay, and a means of measuring relative noise power between the two sources. All bandwidth terms within the receiver used for measurement wash out and you are left with only the actual receiver's noise figure affecting the measurement. One more thing affects your reading - how long is the noise power reading averaged? The longer the more accurate the readings.

MDS measurements are simply a quick and dirty means of estimating noise figure. The receiver noise bandwidth must be known. It must report true RMS values on its signal meter, which is a very rare thing outside of some SDRs. And the long term average readings are required as noted above. Mark 1 eyeball does a damn poor job of averaging noise.

{^_^}

On 20210624 07:36:36, Gedas wrote:

Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED



Re: SDR-Console Power dBm Accuracy

jdow
 

Oh - even that is not needed. Just leave the 6AL5 noise diode powered up any time at all and negative readings are possible. (I was testing something with about a 3/4 dB noise figure 11.5 MHz IF amplifier. The head got hot. So the resistor in it was no longer at room temperature. The results were deep deep into "Say WHAT?" territory until I figured out what was happening.)

{^_^}

On 20210624 01:33:14, Nicholas Shaxted wrote:

With the proviso that the amateur user assumes the calibration sticker is still valid of course.

 

Nick – g4ogi

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of jdow via groups.io
Sent: 24 June 2021 08:28
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SDR-Console Power dBm Accuracy

 

There was a chance he was using the well honed Amateur Radio approach, find some surplus gear and use it. As noted in a different note, HP304B can surprise you.
{^_-}

On 20210624 00:29:47, Bob Dengler wrote:

At 6/24/2021 12:19 AM, you wrote:
Hm, of note the hot and cold noise source CAN become a problem during measurement. You must know both actual temperatures at the time of measurement. The assumed "290K" does not necessarily work. 
T(off) = 290K should be valid, provided there is a well matched attenuator greater than 20 dB between the actual noise diode/tube & the output of the noise source module that's always near (physical) room temperature.
 
Bob NO6B 
 
 
 
 
 

 



Re: SDR-Console Power dBm Accuracy

Bob Dengler
 

At 6/24/2021 04:15 AM, you wrote:
Bob
Thanks. The brand new BBGen noise source is mounted in an rf tight metal box that is peltier temperature controlled at 72 degrees F. Have a brand new JFW 110 dB step attenuator mounted in that same box. No surplus stuff.Â
Larry, K4LEDÂ
The BBGen itself has a VSWR spec of 2:1 on & 10:1 off. Probably a lossy open when off, it's going to need at least 15 dB of attenuation to make it look close to 50 ohms when off. But 15 dB of attenuation will leave barely enough ENR to be usable. I think you'd be better off with a surplus commercial noise source.

Bob NO6B


Re: SDR-Console Power dBm Accuracy

Larry Dodd
 

Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED

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