Date   

Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

I put in a signature from time to time. I've used that glyph so much I usually forget to put a name on it. This comes from being stalked online, for a year, back in 1985. I was issued threats of gruesom rapes and deaths. I stuck it out. He ended up suiciding a fe years later. I'm still here and mostly anonymous as a result. Once Was Enough. (I carried a loaded and ready double action revolver for much of that year. My purse was heavier. The hope was that I'd be the one to come out alive if we ever met in person. It left me - scarred at the least.)

{^_^}   Joanne

On 20210705 19:57:20, oldjackbob@... wrote:
On Mon, Jul 5, 2021 at 07:18 PM, jdow wrote:
SDRC's S-Meter is NOT a proper measurement. It is a usable measurement. But you cannot use it to calculate signal quality in a precise manner. It is CERTAINLY not correct to the IARU definition. He may use the correct attack and decay times on the meter; but, he is not working off the power in the passband.
You're expecting the S-meter to be something it's not. It's not intended to "calculate signal quality in a precise manner", nor is it intended to "work off the power in the passband".

The S-meter is by definition intended to report the highest voltage measured anywhere in the passband. Per IARU Region 1 Technical Recommendation R.1, a signal strength of 50 microvolts is designated as S9 (which correlates to a -73dBm power level assuming an input impedance of 50 ohms) for the HF bands.

Nowhere in the IARU Region 1 spec (or any other document) is "calculation of signal quality" or "total power in the passband" mentioned at all. So someone looking for a "quality of signal" meter would probably be better off just wishing in one hand and...

You keep saying that Simon isn't conforming to the spec but you never offer any specifics. So I'm done with your nonsense (and your meanness) too.

And one more thing - notice how I always sign my name, and you never do, Joanne (and I'm probably spelling it wrong, but there's no way to know because you never sign).

Mark



Re: SNR meter, bandwidth and gain adjustment for transverters

oldjackbob@...
 

On Mon, Jul 5, 2021 at 07:18 PM, jdow wrote:
SDRC's S-Meter is NOT a proper measurement. It is a usable measurement. But you cannot use it to calculate signal quality in a precise manner. It is CERTAINLY not correct to the IARU definition. He may use the correct attack and decay times on the meter; but, he is not working off the power in the passband.
You're expecting the S-meter to be something it's not. It's not intended to "calculate signal quality in a precise manner", nor is it intended to "work off the power in the passband".

The S-meter is by definition intended to report the highest voltage measured anywhere in the passband. Per IARU Region 1 Technical Recommendation R.1, a signal strength of 50 microvolts is designated as S9 (which correlates to a -73dBm power level assuming an input impedance of 50 ohms) for the HF bands.

Nowhere in the IARU Region 1 spec (or any other document) is "calculation of signal quality" or "total power in the passband" mentioned at all. So someone looking for a "quality of signal" meter would probably be better off just wishing in one hand and...

You keep saying that Simon isn't conforming to the spec but you never offer any specifics. So I'm done with your nonsense (and your meanness) too.

And one more thing - notice how I always sign my name, and you never do, Joanne (and I'm probably spelling it wrong, but there's no way to know because you never sign).

Mark


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

Pardon me - 1/2 that number of dB, 1.7609125905568124208128900853062 dB.
{^_^}

On 20210705 19:18:19, jdow wrote:
You do not get it. I can see that clearly, Actually the total power in a 100% modulated pure AM signal is about 3.5218251811136248416257801706124 dB greater than the carrier power alone. (Some perversions allow larger excursions by raising the transmitter's power briefly during signal peaks. That's a cheat.)

The TOTAL power in the bandwidth is what builds your signal plus noise plus distortion reading. That said, no known AM receiver, except (holds her hand up), measures the signal in a manner such as to show this. Diode detectors definitely do not show it. Theory shows it. Spectral analysis shows it. But the simple demodulators do not.

You are trying to hit a special case that matches your view of the picture. SDRC's S-Meter is NOT a proper measurement. It is a usable measurement. But you cannot use it to calculate signal quality in a precise manner. It is CERTAINLY not correct to the IARU definition. He may use the correct attack and decay times on the meter; but, he is not working off the power in the passband. You can see this very dramatically with FM. When the signal to noise ratio falls below 9 dB the signal degrades VERY rapidly. With his S-Meter arrangement that number will be very different.

To be meaningful he must collect all the energy within the receiver passband paying attention to phase as well as amplitude. I've shown the simple way. His way gives results at odds with reality in many edge cases, some of which I see frequently.

(If somebody asks me for a signal report it is always, "59 solid copy, Good Buddy." The tone of voice probably clues some in to the fact that it's a canned response.)

{o.o}

On 20210705 18:47:10, oldjackbob@... wrote:
Joanne,

I probably misspoke at some point if/when I said BCFM carrier is always the greatest power anywhee in teh passband, so I retract any such statement.

However, that statement does hold true for BCAM, so I've captured a video of SDRC's S-meter reporting on a BCAM station:

https://drive.google.com/file/d/1Egb4DyIxXtZNP6rNNKg5PLfQzFTH_7zI/view?usp=sharing

Several key observations:

1) The carrier is very steady.
2) The modulation varies greatly.
3) the passband is intentionally varied between  



Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

Make taht four.
{+_+}

On 20210705 18:47:10, oldjackbob@... wrote:

[Edited Message Follows]

Joanne,

I probably misspoke at some point if/when I said BCFM carrier is always the greatest power anywhere in the passband, so I retract any such statement.

However, that statement does hold true for BCAM, so I've captured a video of SDRC's S-meter reporting on a BCAM station:

https://drive.google.com/file/d/1Egb4DyIxXtZNP6rNNKg5PLfQzFTH_7zI/view?usp=sharing

Several key observations:

1) The carrier is very steady.
2) The modulation varies greatly.
3) The passband is intentionally varied between 2.5k and 12k.
4) The S-meter never varies at all (at least not more than .1dB in any direction).
5) The S-meter is reporting ONLY the peak signal detected anywhere in the passband, nothing more and nothing less.

So tell me where Simon gets it wrong.

Nevermind, that's a loaded question...Simon gets it right.

I'm done here,
Mark


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

All three copies are wrong.
{^_^}

On 20210705 18:47:10, oldjackbob@... wrote:

[Edited Message Follows]
[Reason: Punctuation]

Joanne,

I probably misspoke at some point if/when I said BCFM carrier is always the greatest power anywhee in teh passband, so I retract any such statement.

However, that statement does hold true for BCAM, so I've captured a video of SDRC's S-meter reporting on a BCAM station:

https://drive.google.com/file/d/1Egb4DyIxXtZNP6rNNKg5PLfQzFTH_7zI/view?usp=sharing

Several key observations:

1) The carrier is very steady.
2) The modulation varies greatly.
3) The passband is intentionally varied between 2.5k and 12k.
4) The S-meter never varies at all (at least not more than .1dB in any direction).
5) The S-meter is reporting ONLY the peak signal detected anywhere in the passband, nothing more and nothing less.

So tell me where Simon gets it wrong.

Nevermind, that's a loaded question...Simon gets it right.

I'm done here,
Mark


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 



On 20210705 18:47:10, oldjackbob@... wrote:
I'm done here,
Mark
Fortunately - I am about to become persona non-grata over this nonsense from you.

{+_+}


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

You do not get it. I can see that clearly, Actually the total power in a 100% modulated pure AM signal is about 3.5218251811136248416257801706124 dB greater than the carrier power alone. (Some perversions allow larger excursions by raising the transmitter's power briefly during signal peaks. That's a cheat.)

The TOTAL power in the bandwidth is what builds your signal plus noise plus distortion reading. That said, no known AM receiver, except (holds her hand up), measures the signal in a manner such as to show this. Diode detectors definitely do not show it. Theory shows it. Spectral analysis shows it. But the simple demodulators do not.

You are trying to hit a special case that matches your view of the picture. SDRC's S-Meter is NOT a proper measurement. It is a usable measurement. But you cannot use it to calculate signal quality in a precise manner. It is CERTAINLY not correct to the IARU definition. He may use the correct attack and decay times on the meter; but, he is not working off the power in the passband. You can see this very dramatically with FM. When the signal to noise ratio falls below 9 dB the signal degrades VERY rapidly. With his S-Meter arrangement that number will be very different.

To be meaningful he must collect all the energy within the receiver passband paying attention to phase as well as amplitude. I've shown the simple way. His way gives results at odds with reality in many edge cases, some of which I see frequently.

(If somebody asks me for a signal report it is always, "59 solid copy, Good Buddy." The tone of voice probably clues some in to the fact that it's a canned response.)

{o.o}

On 20210705 18:47:10, oldjackbob@... wrote:
Joanne,

I probably misspoke at some point if/when I said BCFM carrier is always the greatest power anywhee in teh passband, so I retract any such statement.

However, that statement does hold true for BCAM, so I've captured a video of SDRC's S-meter reporting on a BCAM station:

https://drive.google.com/file/d/1Egb4DyIxXtZNP6rNNKg5PLfQzFTH_7zI/view?usp=sharing

Several key observations:

1) The carrier is very steady.
2) The modulation varies greatly.
3) the passband is intentionally varied between  


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

This is why I loved working on GPS, almost the quintessence of time keeping. It's the best answer most people can afford.

{o.o}

On 20210705 18:46:30, Curt Faulk wrote:
Joanne:

I just love your rants. I love them because I'm usually learning quite a bit as I read them.

You provide immeasurable benefit to us all.  I know how much It must pain you to hear me say that... because it is exceedingly apparent how much you like quantifiable measurements.


Re: SNR meter, bandwidth and gain adjustment for transverters

oldjackbob@...
 
Edited

Joanne,

I probably misspoke at some point if/when I said BCFM carrier is always the greatest power anywhere in the passband, so I retract any such statement.

However, that statement does hold true for BCAM, so I've captured a video of SDRC's S-meter reporting on a BCAM station:

https://drive.google.com/file/d/1Egb4DyIxXtZNP6rNNKg5PLfQzFTH_7zI/view?usp=sharing

Several key observations:

1) The carrier is very steady.
2) The modulation varies greatly.
3) The passband is intentionally varied between 2.5k and 12k.
4) The S-meter never varies at all (at least not more than .1dB in any direction).
5) The S-meter is reporting ONLY the peak signal detected anywhere in the passband, nothing more and nothing less.

So tell me where Simon gets it wrong.

Nevermind, that's a loaded question...Simon gets it right.

I'm done here,
Mark


Re: SNR meter, bandwidth and gain adjustment for transverters

Curt Faulk
 

Joanne:

I just love your rants. I love them because I'm usually learning quite a bit as I read them.

You provide immeasurable benefit to us all.  I know how much It must pain you to hear me say that... because it is exceedingly apparent how much you like quantifiable measurements.


Re: SNR meter, bandwidth and gain adjustment for transverters

Robert Lorenzini
 



On 7/5/2021 4:25 PM, jdow wrote:
See my discussion.

Thank you for the education. You put some effort into this and for that I'm gratefull.

Bob - wd6dod


Re: SAQ 17.2 kHz QRV today

PE1OSQ
 
Edited

I try to listen to the SAQ transmissions every year.
For an antenna I hung about 15m of wire from a 2nd floor window to the roof of my shed.
My radio was a KIWI shortwave receiver. The nice thing is that via Youtube you can see
when the transmission starts,

On my kiwi I only heard static noise. No Morse.

Then I switched to my backup "receiver". I plugged the end of the antenna wire into the
microphone jack of my computer soundcard. To receive SAQ I used a free Windows program
called SAQ Panoramic Receiver (v0.98). This worked like a charm! I could hear the
complete morning transmission (11h00 CET). Also the afternoon transmission (14h00 CET)
although with lots of interference from lightning.

Oh how nice it would be if Simons program would support VLF reception via soundcards
in this way.
The picture below is a screenshot of SAQ Panoramic Receiver playing back the RF recording (0-96kHz)

Note: the GREEN line is the RF spectrum. One of the peaks on the right is DCF. The WHITE (actually BLUE)
line is the audio spectrum. No waterfall.


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

See my discussion. I got my wind up and had to work it out making you guys the victims. But it does explain where you are off the reservation and where others have gone off the reservation.

I'll add a little more wind here.

In the digital signals world there are two "domains" that make thinking interesting and provide opportunities. They more or less exist in the old analog design days but were not broken out as well as DSPs allow.

First we have the time domain. In a collection of digital data the values bear a direct relationship to what you perceive with old analog instruments. As you apply successive filters from the front end input filter to the final output filters you capture smaller portions of the overall analog input. At some point you may meter this information. The meter would jump a lot. So you want to average it in some manner. It all seems to flow with our perceptions.

Nyquist and others showed there is a nice relationship between a continuous time set of signals within a defined bandwidth and the data captured with a reasonable number of evenly spaced samples of that continuous set of signals. You can recreate what went in by filtering the output of the digital sampling. The proof depended on the prior work of another fellow.

Long ago a gentleman named Fourier invented some math that showed interesting properties with sampled data. If you sample a sine wave of infinite duration and pass it through his math properly you get a singular value out and a whole bunch of zeros. That singular value is the representation in the frequency domain of that infinitely long sine wave. And thus we have invented the frequency domain view of the world.

Infinity is longer than I, or anybody else, wants to wait. So this has been trimmed down somewhat. If you take a set of samples over time, apply a digitized version of Fourier's math, his transform, you get a frequency domain view of that short time interval. reversing his transform and filtering to remove harmonics and such restores the input, mostly. Some filtering takes place.

Note that the frequency domain picture says nothing about what is happening before or after that set of data. And nothing in the recreated time domain says anything useful about the time outside that original set of samples. SDRs use this effect by taking successive sets of data, transforming to the frequency domain, manipulating the new representation of the data, and then restoring the sets in order. It's difficult to wrap one's head around the concept that what comes out of this is a good and accurate representation of what came in. However, it does work.

So this is what I meant, in brief, by the time domain vs the frequency domain in my prior pontification. The frequency domain portion of an SDR breaks a limited chunk of time into a spectrum including amplitude and phase information representative of the limited time set of samples. Manipulating frequency in the time domain is awkward. Manipulating time in the frequency domain is awkward.

One data value in time or frequency means nothing in particular in the frequency or time domains respectively. You cannot take one frequency data point and call it representative of signal level during that time interval. You need to use the time domain to get the quasi-peak data IARU requires.

With regards to your questions about the measurements I suggested with NFM and BFM suggest you are in over our current level of knowledge. FM modulation schemes spread the bandwidth of signals over a wider frequency range than the modulating signal. With a single sine wave modulation the spectrum takes on a (theoretical) infinite number of sidebands on integer multiples of the modulating signal. As the level of modulation increases from zero the various sidebands and the carrier go up and down through nulls in which the carrier or pairs of sidebands, upper and lower for a given multiple, falls to a zero value. In general intuition is validated as high order sidebands have very very low amplitudes until the frequency deviation becomes significant relative to the sideband's difference from the carrier. Because of this effect BFM signals can show "single spectral element" peak selection 20 dB or more below what you see during silence broadcast with carrier only. The S-Meter value should not show that kind of change. (And even on AM the S-Meter in principle should show more power on very weak signals as you make the bandwidth wider. After all, it is a meter reading signal plus noise in the selected "IF" bandwidth. And hooboy I don't want to get off on digital modulation schemes. Those skills are close to defunct through lack of use over the most recent 20 years.)

{^_^}
A little more below

On 20210705 14:49:08, oldjackbob@... wrote:
Joanne,

I didn't "go off the cliff" anywhere.

1) "So if you have a signal that features multiple peaks all about the same amplitude how big is the S-Meter error?" What "error" are you referring to?? There is no "error". In the case you describe (with multiple equal peaks), the S-meter should read the same regardless of whether there are one or a thousand peaks. As I've stated unwaveringly, the S-meter should report the highest value detected anywhere in the passband, no more and no less. What part of that rule is not clear to you? It's clear to me by your very question that you don't have the slightest grasp on that simple rule.

Actually the meter will not read the same. Observe the spectrum behavior of a broadcast FM station as it goes from relative silence to full deviation. The meter will drop 20 dB or more even though the power received remains the same.

2) "Take an NFM signal modulated by a sine wave. Run up the modulation from zero until there are three spikes showing within the NFM bandwidth that are all the same level. What is the correct measurement? One of the peaks or the proper sum of all three?" What is this "proper sum of all three" value you mention??? Be specific. Your prized "sum" value remains undefined.

This is the problem with reconstructing the "power" reading when you consider power readings of the individual terms of an FFT. Some are incoherent, as with noise, and some are coherent as with the example. With an FM signal the proper sum will remain constant not drop by several dB.

3) "Now continue running up the amplitude of modulation into the BFM realms with the signal spread out over 200 kHz bandwidth. What is the correct S-Meter reading?" What is even the point of that question? The S-meter couldn't (and shouldn't) care less about bandwidth.

You are wrong here on several levels. I touch on this above.

4) "Does that reading change when the announcer pauses for breath? Should it?" The simple answer is "no", at least not for a transmission with a steady FM carrier, given that by definition the modulation on any FM signal should never exceed the strength of the carrier. Once again - the S-meter should only report the strongest signal measured anywhere in the passband. For an FM (or AM) signal, the strongest signal will always be the carrier.

I am SERIOUSLY struggling to not be abusive. But this requires an answer. You are absolutely and comprehensively wrong. I hope my explanations have shown you at least a hint of how wrong you are.

You're asking me these questions, but you (or anyone else) can easily see the answers to every one of those questions by simply opening a session of SDRC and click on any BCFM or BCAM station. If the carrier is steady then the S-meter reading will also be steady, regardless of the amount of modulation and regardless of bandwidth.

I have an SDR implementation that works the way it should measuring power within the last IF's effective bandwidth. It behaves exactly as I define it, power within the last IF's bandwidth. With FM signals this stays constant as it should. The POWER received for FM modulation does not change with time. It's pretty clear to me that you do not understand what the Fourier Transform or its derivatives provide you when viewing a signal. It is not successive views in time by any stretch of the imagination. You seem to think it is. I hope I expanded your digital horizons a little. And I hope it was worth it.

If anyone has gone off a cliff, it certainly isn't me!
 
https://www.youtube.com/watch?v=y50i1bI2uN4

(And, yes, I do fall victim to that from time to time. Everybody does. I figure I know something about radio as I've been involved with them and designing them for over 60 years.)

{o.o}


Re: SNR meter, bandwidth and gain adjustment for transverters

Bob Dengler
 

At 7/5/2021 03:28 PM, you wrote:
WTFF is "Continuum mode". You are losing your audience by inventing terms that make no sense. Do you mean time domain where everything flows along in a sampled stream? If so then time domain makes more sense to the engineers designing things. It's instantly understandable. {+_+}
I thought perhaps he was referring to omnipotent signals.

-Q


Re: 3D waterfall

Kriss Kliegle KA1GJU
 

Found the lead from the charger arcing where it attaches to the fence. Put two stainless steel washers and a 1/4 stainless bolt and nut on it. Clamped the hell out of it.
On my way to KSFO (San Francisco) right now, will read thread in 6 hrs from now.
Maybe 17m open for some AM work?

73 KA1GJU/AM


Re: 10 kHz-150 kHz Band Sweep from EN70 Indiana

D R
 

Hi Gedas,

Can you post a recording direct from SDRC, please?  It would be nice to be able to dive into the waterfall and look at some of the weak signals close up, although it was easy enough to pick out all the US Navy stations (and some French Navy as well).  A five minute duration is ample, and it keeps the filesize down to about 200MB.

I've added another recording I've just made - the solar panels are gone, the storms aren't too bad, and the LORAN transmitter is back on, but well below its normal power output, so it's all reasonably clear.  DDH47 on 147.3kHz is worth a look, as you can decode it with FLDigi (settings:  RTTY - Custom - 85Shift, 50baud, 5-0-1.5, Auto, 72char.  Use CW or LSB, filter centred on signal.)  I haven't checked it myself to see whether it was actually sending anything worth decoding, but I could always do a much longer recording if you want to try it out (German weather forecasts can make rivetting reading ;) ).

Regards,
Dave


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

But S-Meter is not SNR meter. Although the SNR meter should be approximated from the S-Meter reading.

{^_-}

On 20210705 13:57:05, Conrad, PA5Y wrote:

Well I disagree, SNR improves as you reduce bandwidth, this is just physics. If the metering does not reflect this then the SNR metering is simply wrong. Just use your ears.

 

Conrad

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of oldjackbob via groups.io
Sent: 05 July 2021 16:43
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SNR meter, bandwidth and gain adjustment for transverters

 

Per the info on Simon's page explaining the operation of the S-meter, "[The signal level] is the peak spectrum FFT bin (output value) which is within the current filter."

That page is found here: https://www.sdr-radio.com/s-meter

Simon explains it clearly. There is no correlation of peak FFT bin value to filter bandwidth (or AGC level, or any other consideration), nor should there be. Any modern SDR-based S-meter that changes its reading based on filter bandwidth is doing it wrong.

I've said it before: Simon got it right, many others are getting it wrong.

Mark

 



Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

On 20210705 12:09:22, Bob Dengler wrote:
At 7/5/2021 10:43 AM, you wrote:
On Mon, Jul 5, 2021 at 09:26 AM, Bob Dengler wrote:
I strongly disagree. How else is one supposed to make total channel power measurements for radiometry? SDRs aren't just for communications, & any developer that codes their SDR apps otherwise is hamstringing their full potential. Right now the only apps I know of that can do this are HDSDR & SDRuno. HDSDR is compatible with all my SDRs so that covers my needs, but it would be nice if SDRC could display & record average channel power readings as well as HDSDR is fairly useless for NBFM monitoring (no de-emphasis).

I'll have to go through the forum archives to see if this has been requested, & do so if not.

Bob NO6B

Please define "average power". I've also seen the term "integrated power" bandied about in the Flex forums. There is no established definition for either term.
We can choose to split hairs on average vs. sample vs. RMS.  I think for purposes of amateur radiometry, any of the above will do.  If I'm wrong someone please chime in.

The function of an S-meter is not to report the "total power" or "average power" or "integrated power" in the passband, it is to report the highest voltage measured anywhere in the passband, irrespective of any nebulous "total power" contained within the filter. That's what Simon's S-meter does.
OK, fair enough.

An S-meter, as described above, is useless to me.  I would like to see the option of switching the S-meter function in SDRC to an average channel power meter.  

:)

Thanks

Bob NO6B 

Please, Bob, distinguish what you mean with reference to time domain or spectral domain. It all makes SO MUCH more sense in time domain. Then terms like "quasi peak" make sense. It's meter rise time written usefully. That term makes no sense in the frequency domain.

Please PLEASE *P*L*E*A*S*E* guys distinguish between frequency domain behavior and time domain behavior. Frequency domain behavior gets in there when Simon discusses picking one small frequency bin to represent the whole bandwidth of interest.

{o.o}


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

WTFF is "Continuum mode". You are losing your audience by inventing terms that make no sense. Do you mean time domain where everything flows along in a sampled stream? If so then time domain makes more sense to the engineers designing things. It's instantly understandable.

{+_+}

On 20210705 12:27:26, sm6fhz wrote:
Hi.
I made a request for this (Continuum mode) in 2014 together with a basic specification of possible functions.
It can be found here:
https://sdr-radio.groups.io/g/main/message/23048
I hope it can make a baseline fore further development of a in dept specification.
73 / Ingolf, SM6FHZ


Re: SNR meter, bandwidth and gain adjustment for transverters

jdow
 

I'm sorry guys - my autisim has kicked in and I have to get this off my chest before I explode.

As originally conceived the S-Meter was an indication of channel power. Meter ballistics and capacitor charge and discharge created a quaisi-peak reading over time. It takes a little time for the meter reading to rise and it generally if not originally takes longer to fall.

This served multiple purposes. I'm not sure which came first, protecting the operator's ears or providing a relative power indication for the operator. I suspect the latter was easier to implement before the days of AGC systems. Certainly IF alignment is facilitated by reading audio output power with any AGC disabled. Probably somebody figured that would be handy for operators to give some relative power readings during active communications. In some radios special meter calibration was used to give quasi accurate readings 6dB/S-unit. That did not sell so we got the 2 dB per S-Unit of the ProII coming out of the mess. (I have one so I pick on it's shortcomings.)

The important point above is that the S-Meter responds to instantaneous power changes slowly. This gives it the IARU's quasi-peak sort of performance much like a VU meter provides, as perhaps distinct from a Durrough meter. The value you see on the meter bears a fairly good indication, if the meter is accurate, of you real ability to communicate.

Once we move to the spectral domain from the time domain this "quasi-peak" loses meaning. It has to be applied between successive spectral computations. Since there are FFT peculiarities such as windowing involved it is difficult enough to be called impossible or at least quite impractical to make real accurate readings for say a 2.4 kHz bandwidth out of a spectrum with 10 Hz bins.

Fortunately in most cases one filters incoming data before switching to baseband processing. In the case of SSB it's a zero IF receiver so filtering after conversion can be used but power can be derived in much the same way. Take the IF filter output IQ values, square each one, and add them together. That is a real power value in dB relative to a dooby value. With a calibrated source the dooby value can become a real dBm value. (For AM demodulation the square root of that power value becomes your AM output without the distortion products the usual diode demodulators provide.)

Once you have that power value derived from I^2 + Q^2 you can filter it per the IARU quasi peak requirements and get correct S-Meter readings and behavior.

Do note that the I^2 + Q^2 reading above is NOT necessarily well related to selecting the highest level bin in an FFT output. With broadcast FM it very emphatically does not. I have seen peak spectral element values on a broadcast FM signal vary by more than 20 dB from silence to high modulation level. That is not in any way shape or manner proper S-Meter behavior.

Now maybe I can get this out of my head. I hope I did not get abusive above. (This is why I enjoy math. There is only one correct answer or set of answers. It's the way my brain works. And it's made my life "complicated" to say the least.)

{O.O}

On 20210705 12:02:37, Bob Dengler wrote:
At 7/5/2021 09:37 AM, you wrote:
Bob,

Is this Continuum mode? I would need an exact specification were I to add
this.
Not sure if I understand the question.  I'm referring to the channel power or S-meter, which if I understand correctly current indicates peak channel power.  It would be nice to have the option to have it read average channel power, then also have the ability to store those readings to a CSV file (2 columns: time & dBm) every x milliseconds.  This is exactly what HDSDR offers.  Once calibrated with a known noise source or hot/cold load, this allows using an SDR as a radiometer.  Also give us one or two significant digits after the dBm decimal point.

I'll put the above in the SDRC Requests forum if needed.  Thanks!

Bob NO6B 

2181 - 2200 of 65214