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  


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