S-Meter calibration #airspyhfplus #sdrconsolev3


Die Solinger <diesolinger@...>
 
Edited

Hi guys,

I wonder if any of you have calibrated the S-Meter of SDR Console V3 for the Airspy HF+? At the moment I did it by feel, because I don't have a signal generator. But I would like to set it correctly, so if you can tell me the values of the Visual Gain, please give it to me! At the moment I only work with it in the HF range, if that is important. Thanks in advance.


jdow
 

If you use AGC (grudgingly recommended) calibration may be an awkward item because correcting for the front end AGC requires feedback from the HF+ for its current gain. Without AGC calibrated signal generator and visual gain setting.

{^_^}

On 20200625 08:02:06, Die Solinger via groups.io wrote:
Hi guys,
I wonder if any of you have calibrated the S-Meter of SDR Console V3 for the Airspy HF+? At the moment I did it by feel, because I don't have a signal generator. But I would like to set it correctly, so if you can tell me the values of the Visual Gain, please give it to me! At the moment I only work with it in the UHF/VHF range, if that is important. Thanks in advance.


Simon Brown
 

And,

Just what I was going to say. The HF+ (and others such as Pluto, SDRplay) radios uses a tuner chip, so although you could get reasonable calibration AGC and similar will cause problems.

FWIW if you want a radio you can calibrate then direct sampling is probably what you need.

Simon Brown, G4ELI
https://www.sdr-radio.com

-----Original Message-----
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of jdow
Sent: 25 June 2020 16:31
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] S-Meter calibration #sdrconsolev3 #airspyhfplus

If you use AGC (grudgingly recommended) calibration may be an awkward item because correcting for the front end AGC requires feedback from the HF+ for its current gain. Without AGC calibrated signal generator and visual gain setting.

{^_^}

On 20200625 08:02:06, Die Solinger via groups.io wrote:
Hi guys,

I wonder if any of you have calibrated the S-Meter of SDR Console V3
for the Airspy HF+? At the moment I did it by feel, because I don't
have a signal generator. But I would like to set it correctly, so if
you can tell me the values of the Visual Gain, please give it to me!
At the moment I only work with it in the UHF/VHF range, if that is important. Thanks in advance.


Die Solinger <diesolinger@...>
 

OK, I read that SDR Uno has a calibrated S-Meter with the HF+. How does this work if it's impossible to calibrate?

Btw, I never use AGC with my HF+.


Simon Brown
 

Hi,

 

It’s not impossible, just no guarantee that calibration is accurate under all signal conditions, especially strong signals. Myself, HF+ and SDRplay radios show consistent values.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Die Solinger via groups.io
Sent: 25 June 2020 16:43
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] S-Meter calibration #sdrconsolev3 #airspyhfplus

 

OK, I read that SDR Uno has a calibrated S-Meter with the HF+. How does this work if it's impossible to calibrate?

Btw, I never use AGC with my HF+.


Die Solinger <diesolinger@...>
 
Edited

Would it work with an RSP1A to calibrate the S-meter of SDRC3? (For VHF/UHF)


Alan
 

On 25/06/2020 15:02, Die Solinger via groups.io wrote:
At the moment I only work with it in the UHF/VHF range, if that is important
As Joanne says it is. No AGC is used at VHF.
But the only way on HF with a HF+ is to set the gain manually and compensate.
I think somewhere in the Airspy group are details of how to gauge signal levels by using the noise floor of the HF+ as a reference. The noise floor is reckoned to be fairly constant between HF+s.
I did not take note of it because I do have a roughly calibrated reference.

73 Alan G4ZFQ


Jon Hudson
 

You can always check using SDRuno and an RSP on a steady signal in a particular band. Then for that band, any differences with the SDR Console reading can be be factored in.  

By the way, regarding the SDRuno S-meter reading - it gives a measurement of the total signal power within the demodulation bandwidth.  

 

 

The S-meter and associated power meter in SDRuno are calibrated to the IARU standard which is that S9=-73 dBm for signals at 30 MHz or below and S9=-93 dBm for frequencies above 30 MHz. The accuracy of the power measurement is typically 1 dB across all gain settings, which is a fraction of an S-unit. This is what also allows the  RSPs to be used as very respectable RF power meters.   The same principle is used to allow calibrated readings in the Spectrum Analyser: https://www.sdrplay.com/spectrum-analyser/ 


73,  Jon G4ABQ

 


jdow
 

(BY the way, if there is an accurate S-Meter out there outside of SDRs I'd be astonished. ICOM Pro IIs are about 2 to 3 dB per S-Unit up to S9 and then suddenly become close to 10 dB/10dB on the over S9 reports. Maybe they are trying to accommodate the very high natural noise levels on 75 meters or something. I'd not worry about it. Signals are always "60 dB over S9, OM.")

{^_-}

On 20200625 08:02:06, Die Solinger via groups.io wrote:
[Edited Message Follows]
Hi guys,
I wonder if any of you have calibrated the S-Meter of SDR Console V3 for the Airspy HF+? At the moment I did it by feel, because I don't have a signal generator. But I would like to set it correctly, so if you can tell me the values of the Visual Gain, please give it to me! At the moment I only work with it in the HF range, if that is important. Thanks in advance.


jdow
 

If you cannot measure it how do you know it is calibrated?
{O.O}

On 20200625 08:42:41, Die Solinger via groups.io wrote:
OK, I read that SDR Uno has a calibrated S-Meter with the HF+. How does this work if it's impossible to calibrate?
Btw, I never use AGC with my HF+.


jdow
 

Then we have the question, "how do they calculate signal level?" What do they show on the spectrum? Total power per display pixel is a number I can relate to. But that CAN hide narrowband signals. And so forth.

And of course the same signal volts/meter at the antenna condition can give quite different values at the receiver input. At microwaves this is particularly dramatic and at HF the difference between a beam and a small loop can be somewhat dramatic. So for the ham sending the signal what does the S meter reading really tell him?

I better stop - I am starting to get the urge to mess with minds.

{^_-}

On 20200625 09:16:41, Jon Hudson wrote:
You can always check using SDRuno and an RSP on a steady signal in a particular band. Then for that band, any differences with the SDR Console reading can be be factored in.
By the way, regarding the SDRuno S-meter reading - it gives a measurement of the total signal power within the demodulation bandwidth.
The S-meter and associated power meter in SDRuno are calibrated to the IARU standard which is that S9=-73 dBm for signals at 30 MHz or below and S9=-93 dBm for frequencies above 30 MHz. The accuracy of the power measurement is typically 1 dB across all gain settings, which is a fraction of an S-unit. This is what also allows the  RSPs to be used as very respectable RF power meters.   The same principle is used to allow calibrated readings in the Spectrum Analyser: https://www.sdrplay.com/spectrum-analyser/
73,  Jon G4ABQ


Jon Hudson
 

Hi again .

So I think we are close to agreement. Just to clarify: 

The SDRuno S-meter gives a measurement of the total signal power within the demodulation bandwidth.  As jdow says, it can indeed hide the true strength of a narrowband signal. This is because the software is incapable of distinguishing between a wanted signal and all the interference within the same bandwidth and so it is perfectly possible to have a reading of S9+20 and have a barely audible signal of interest. S-meters give a measurement of power and not signal quality and 'twas ever thus'.  So it's important to tweak the passband to just include the signal whose strength you want to measure - you then get an accurate reading.  If that's not possible, your measurement is probably of little interest.

 

So for those suggesting that the S-meter is useless as an accurate indicator of signal quality, then you are quite correct. After all that's why they invented the RST scale - R1, S9 is a no copy.

However, If you are questioning whether it provides a reasonable accurate measurement of total RF power within the demodulation bandwidth (as defined in the SDRuno case,  by the SP2 filter setting) then you are incorrect. With RSPs and SDRuno, it's spot on :-)

Jon, G4ABQ


Ron Liekens
 

A bit beside the discussed thread, but related, is that the only real thing for me on which I rely is the SNR indication which is both a nice feature on SDRuno and SDRconsole. Also your ears are not to be fooled!

Ron, ON2RON