Topics

tx / rx freq offset with Pluto #pluto

kt6uk
 

Hi guys,

I've been experimenting with Pluto through es Hail on ssb and have run into a small snag.

I'm running the latest version of SDR console under Windows 10 64 bit.

Despite setting the tx freq to sync to the rx freq when I transmit the signal comes out about 35kHz lower. I can compensate for this by setting the XIT.

Any pointers as to what I need to tweak to avoid using the XIT fudge?

73 Tim G4WIM

Simon Brown
 

Hi,

 

https://www.sdr-radio.com/Support screenshot please, let’s see what you’ve done so far.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of kt6uk
Sent: 09 September 2019 21:51
To: main@SDR-Radio.groups.io
Subject: [SDR-Radio] tx / rx freq offset with Pluto #pluto

 

Hi guys,

I've been experimenting with Pluto through es Hail on ssb and have run into a small snag.

I'm running the latest version of SDR console under Windows 10 64 bit.

Despite setting the tx freq to sync to the rx freq when I transmit the signal comes out about 35kHz lower. I can compensate for this by setting the XIT.

Any pointers as to what I need to tweak to avoid using the XIT fudge?

73 Tim G4WIM

Siegfried Jackstien
 

just a guess ... your lnb is off by 35 kc but you typed in 9.75 gig ?!?

if you found out with the rit (not the xit) that you are 35 off ... set that correection in the lnb definition ...

if you are off by 35 kc and checked that say with a web sdr (and it is NOT your lnb setting) ... then you have to tune the ppm setting of the pluto

seting an offset of 35 kc is NOT right then ... you HAVE TO tune the ppm value

go into radio configuration (tx options/plutosdr/radioconfiguration) ... second entry (calibration)

that is set to 40 megs by default

but your pluto maybe is 39.99something??

here you finetune your tx frequency ...(it also changes rx)

click on apply updates when connecting and on enable updates

with finetune the ppm value plus or minus ... tune your tx frequency till it is spot on on the web sdr ...

now you will see a cmplete different lnb frequency also but that can be compensated in the radio definitions with typing in a different lnb offset

ok ... with ppm you tune your tx and rx ... with downconverter you tune the lnb offset ...

if both are set well you should be spot on ... and well transceive

hth

dg9bfc sigi

Am 09.09.2019 um 20:51 schrieb kt6uk:

Hi guys,

I've been experimenting with Pluto through es Hail on ssb and have run into a small snag.

I'm running the latest version of SDR console under Windows 10 64 bit.

Despite setting the tx freq to sync to the rx freq when I transmit the signal comes out about 35kHz lower. I can compensate for this by setting the XIT.

Any pointers as to what I need to tweak to avoid using the XIT fudge?

73 Tim G4WIM

kt6uk
 

Hi Sigi,

thanks for your offer of help.

I suspect its related to how the sync Rx and rx>tx is working or more likely my not understanding how it should work !

I have a Lime and a Pluto - the Lime works fine with no offsets.

Then I selected the Pluto and again worked fine with maybe only a few hundred Hz offset.

I have the system locked to be beacon so all the frequency offsets should be ok and the beacon appears where is should be.

So this issue with Pluto is likely a sync rx problem as it seems to come and go.

Not sure what screen shots would help resolve this problem - if it is indeed a problem and not a 'operator problem'.

73 Tim G4WIM

kt6uk
 

Replying to myself here - ok so I figure something odd is going on with the Pluto.

Here's what I do and what happens.

1. Start the system up for pluto and enable beacon frequency lock - beans shows to be on exact freq and stays there.
2. Place the green cursor over a signal and fine tune to resolve as it should be.  RX freq shows on in rx window.
3.  In the tx window click on top middle button to sync rx > tx, the frequency in the tx window changes to match that of the rx. eg 10.489.760.500
4  Go onto tx and the transmit freq is some random number of kHz offset usually lower - anywhere from 10 to 35kHz.  Happens with both voice and tune signals.
5.  Repeat 2,3 and 4 and same offset on tx appears.

Seems as though the tx freq is not being set correctly ?

Any ideas?

73 Tim G4WIM

jdow
 

If you are going to attempt to correct for oscillator variations then you absolutely MUST be aware of which frequencies the oscillator controls. One must also be aware of what any ppm or other correction affects which oscillator or which part of the receive system.

Zeroing the Pluto before worrying about the 10 GHz frequency is mandatory for best results. (And unmodified Plutos are rather dreadful.) The SDRC calibration is NOT for 10 GHz signals. It is for the frequency at the input (and output) of the Pluto itself. PPM setting corrections end at the Pluto connectors.

With that understanding please do not attempt to correct converter errors, calculate a PPM setting based on converter input or output frequencies, or otherwise involve converters in your PPM thinking.

Once Pluto is setup and as accurate as you can get it, which is admittedly fairly poor, THEN you adjust the receive conversion frequency offset in the receiver definitions. Do NOT repeat NOT fiddle with PPM settings at that point or you will destroy your system calibration and experience mysterious errors.

If you are 100% certain that your converter is "right on" then you can cheat the process and "assume" (we know that word triplet) we can enter the known exact converter offset, to the Hz, in the definition. Then do not even think of calculating PPM offset and trying to enter it. Simply tune SDRC to frequency and tune the signal to an exact setting using the Calibration panel. Don't even bother to look at the actual figure. The process assures it is correct.

It sounds to me like you are trying to make a simple procedure far far more complicated than it really is because of a false assumption somewhere in your thinking process. It really is simple. Calibrate SDRC at the Pluto input (output takes care of itself.) Then correct offsets with the offset setting in definitions.

And please do be aware that the Pluto itself is no more stable than an rtlsdr dongle. It'll be somewhere probably within 100 PPM of correct and will vary with local temperature by as much as 10s of PPM.

{o.o}

On 20190910 02:47:31, kt6uk wrote:
Hi Sigi,
thanks for your offer of help.
I suspect its related to how the sync Rx and rx>tx is working or more likely my not understanding how it should work !
I have a Lime and a Pluto - the Lime works fine with no offsets.
Then I selected the Pluto and again worked fine with maybe only a few hundred Hz offset.
I have the system locked to be beacon so all the frequency offsets should be ok and the beacon appears where is should be.
So this issue with Pluto is likely a sync rx problem as it seems to come and go.
Not sure what screen shots would help resolve this problem - if it is indeed a problem and not a 'operator problem'.
73 Tim G4WIM

Siegfried Jackstien
 

some user do it exactly the wrong way

they first set the lnb to 9.750 (first wrong guess)

then they compensate the rx offset with the ppm value in pluto calibration (another wrong thought cause you have to check the pluto not the system with the ppm setting)

and then they wonder why they are not a few hundred hertz but 35 kc off

WRONG WAY

MODDING THE PLUTO IS NEEDED ANYWAY!!!

either external reference or change internal tcxo (and then they can become quite stable ... wink wink)

if you can tx on the sat ... then do a test transmission and set ppm value of the pluto that tx is spot on (that way the lnb offset does not influence your calibration and you check ppm value on 2.4 gig and not on 740 megs ... so it should be more accurate)

after tx is spot on ... you then can check lnb offset

cause you now the pluto is tuned well in its ppm settings you NOW can use it to measure the lnb offset ... just type in that offset in definitions ... and you should be spot on in rx and tx

hth

dg9bfc sigi

Am 10.09.2019 um 17:28 schrieb jdow:

If you are going to attempt to correct for oscillator variations then you absolutely MUST be aware of which frequencies the oscillator controls. One must also be aware of what any ppm or other correction affects which oscillator or which part of the receive system.

Zeroing the Pluto before worrying about the 10 GHz frequency is mandatory for best results. (And unmodified Plutos are rather dreadful.) The SDRC calibration is NOT for 10 GHz signals. It is for the frequency at the input (and output) of the Pluto itself. PPM setting corrections end at the Pluto connectors.

With that understanding please do not attempt to correct converter errors, calculate a PPM setting based on converter input or output frequencies, or otherwise involve converters in your PPM thinking.

Once Pluto is setup and as accurate as you can get it, which is admittedly fairly poor, THEN you adjust the receive conversion frequency offset in the receiver definitions. Do NOT repeat NOT fiddle with PPM settings at that point or you will destroy your system calibration and experience mysterious errors.

If you are 100% certain that your converter is "right on" then you can cheat the process and "assume" (we know that word triplet) we can enter the known exact converter offset, to the Hz, in the definition. Then do not even think of calculating PPM offset and trying to enter it. Simply tune SDRC to frequency and tune the signal to an exact setting using the Calibration panel. Don't even bother to look at the actual figure. The process assures it is correct.

It sounds to me like you are trying to make a simple procedure far far more complicated than it really is because of a false assumption somewhere in your thinking process. It really is simple. Calibrate SDRC at the Pluto input (output takes care of itself.) Then correct offsets with the offset setting in definitions.

And please do be aware that the Pluto itself is no more stable than an rtlsdr dongle. It'll be somewhere probably within 100 PPM of correct and will vary with local temperature by as much as 10s of PPM.

{o.o}

On 20190910 02:47:31, kt6uk wrote:
Hi Sigi,

thanks for your offer of help.

I suspect its related to how the sync Rx and rx>tx is working or more likely my not understanding how it should work !

I have a Lime and a Pluto - the Lime works fine with no offsets.

Then I selected the Pluto and again worked fine with maybe only a few hundred Hz offset.

I have the system locked to be beacon so all the frequency offsets should be ok and the beacon appears where is should be.

So this issue with Pluto is likely a sync rx problem as it seems to come and go.

Not sure what screen shots would help resolve this problem - if it is indeed a problem and not a 'operator problem'.

73 Tim G4WIM

kt6uk
 

ok - got it sorted now.

I calibrated the Pluto against my GPS locked sig gen on 739.550MHz (beacon IF freq)  had to apply a -6.875ppm adjustment.
Then went back to satellite mode and adjusted the 9750 LNB offset to 9750501 to get the beacon where it should be.

Tried SSB and still had a few hundred Hz offset so tweaked the ppm another 0.1 or so until my voice sounded ok on down link.

Fingers crossed should be ok now.

I had wrongly assumed that the ppm in the Pluto wouldn't matter as all the offsets and drift etc would be taken care of in the SDR V3.

Thanks again

73 Tim

Siegfried Jackstien
 

no ... the beacon lock can only take care of your lnb drifting ... but not if your master clock in the pluto is off (how should soft know if the error comes from the lnb or from the master clock)

so ... you tune ppm till tx is right ... them tweak lnb setting till beacon is spot on ... then you lock to beacon ... and finetune the ppm setting as accurate as possible ...

smallest step in the xo correction is 1hz in 40 megs ... or it is 60hz in 2.4 gig ...

so tune the ppm as accuate as possible leaving a fault of max 30 hz and then you are set

(finetuning last 30 hz can be done with xit function in the soft)

greetz sigi dg9bfc


Am 10.09.2019 um 19:22 schrieb kt6uk:

ok - got it sorted now.

I calibrated the Pluto against my GPS locked sig gen on 739.550MHz (beacon IF freq)  had to apply a -6.875ppm adjustment.
Then went back to satellite mode and adjusted the 9750 LNB offset to 9750501 to get the beacon where it should be.

Tried SSB and still had a few hundred Hz offset so tweaked the ppm another 0.1 or so until my voice sounded ok on down link.

Fingers crossed should be ok now.

I had wrongly assumed that the ppm in the Pluto wouldn't matter as all the offsets and drift etc would be taken care of in the SDR V3.

Thanks again

73 Tim

kt6uk
 

Hi Sigi I though the beacon lock could take care of both the lnb and master pluto clock by adjusting the tuned frequency of the Pluto for both tx and rx as indeed it must be doing to compensate for the lnb drift and error. All working pretty well now apart from some residual drift in the Pluto so plan on changing the 40MHz ref osc to one of these  ASTX-13-C-40.000MHz-I05-T which should give better than 0.5ppm stablity

Look forward to working you on the sat !

73 Tim

jdow
 

I'd leave the ppm value alone. That way when you shift frequency by 1 MHz you get 1,000,000 Hz and not some small amount different. Actually for the satellite your "cheat" with ppm is probably safe as you're not moving frequencies very far. For 0.1 ppm moving 250 kHz the error would be closer than measurable. Being me it would trouble me to do that on the basis that something might be off a bit.

Something else to remember is that on all these units the synthesizers do not have a constant step size let alone a 1 Hz step size. For example the R820T tuner in AirSpy and most rtlsdr dongles has an approximate step size of about 7 Hz. Ideally the SDR would read back what the actual frequency setting was and adjust itself so that the display would be accurate. My rtlsdr.dll can provide that data. I don't know that AirSpy can do it. So there is a limit to how precise you can get these silly things.

(I'd make the correction you needed in the radio definition on the basis that SOMEDAY I will want to use that converter at a frequency far enough distant from the current satellite usage that the ppm error introduced would matter in some way. But, then, I'm the goof that designed the phase IIb GPS satellite frequency synthesizer and as a result have my head all screwed up on what accuracy is really needed.)

{^_-}

On 20190910 12:22:52, kt6uk wrote:
ok - got it sorted now.
I calibrated the Pluto against my GPS locked sig gen on 739.550MHz (beacon IF freq)  had to apply a -6.875ppm adjustment.
Then went back to satellite mode and adjusted the 9750 LNB offset to 9750501 to get the beacon where it should be.
Tried SSB and still had a few hundred Hz offset so tweaked the ppm another 0.1 or so until my voice sounded ok on down link.
Fingers crossed should be ok now.
I had wrongly assumed that the ppm in the Pluto wouldn't matter as all the offsets and drift etc would be taken care of in the SDR V3.
Thanks again
73 Tim

Siegfried Jackstien
 

use the asVtx 13 c 40.000 i05 t (the v is ... it has a tune pin

that pin is left floating original in pluto so you can add a 10 turn trimmer and never ever mess again with ppm setting but finetune with a tiny screwdriver instead

i already sent you some pics in direct mail

greetz sigi dg9bfc

ps .. hopefully we work AFTER you changed the tcxo ... do not wanna add a powerdrill to my vfo hi hi

Am 10.09.2019 um 20:53 schrieb kt6uk:

Hi Sigi I though the beacon lock could take care of both the lnb and master pluto clock by adjusting the tuned frequency of the Pluto for both tx and rx as indeed it must be doing to compensate for the lnb drift and error. All working pretty well now apart from some residual drift in the Pluto so plan on changing the 40MHz ref osc to one of these  ASTX-13-C-40.000MHz-I05-T which should give better than 0.5ppm stablity

Look forward to working you on the sat !

73 Tim

Simon Brown
 

Tim,

 

I’ll try to help you if you post a screenshot as an attachment; this must show the Pluto settings.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of kt6uk
Sent: 10 September 2019 14:39
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] tx / rx freq offset with Pluto #pluto

 

Replying to myself here - ok so I figure something odd is going on with the Pluto.

Here's what I do and what happens.

1. Start the system up for pluto and enable beacon frequency lock - beans shows to be on exact freq and stays there.
2. Place the green cursor over a signal and fine tune to resolve as it should be.  RX freq shows on in rx window.
3.  In the tx window click on top middle button to sync rx > tx, the frequency in the tx window changes to match that of the rx. eg 10.489.760.500
4  Go onto tx and the transmit freq is some random number of kHz offset usually lower - anywhere from 10 to 35kHz.  Happens with both voice and tune signals.
5.  Repeat 2,3 and 4 and same offset on tx appears.

Seems as though the tx freq is not being set correctly ?

Any ideas?

73 Tim G4WIM

kt6uk
 

Hi Simon,

I have it working ok now (I think)  - just a bit of residual drift / wobble from the Pluto which I will fix by changing out the reference..


I'll get the Pluto settings just in case I'm missing something.

73 Tim

PS hope the dogs like the paypal dog food ;-)

kt6uk
 

Hi Sigi

thanks for the email and detailed instructions - I'll be ordering the components later today once I've discovered what type of case you used.

73 Tim