Re: SNR meter, bandwidth and gain adjustment for transverters


jdow
 

On 20210705 10:43:26, oldjackbob@... 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.

The total power in a given bandwidth cannot be properly derived from a spectrum display. It can be derived easily from a filter followed by demodulator design. You take the I and Q values, square them, and sum them. That gives you the power in arbitrary units that can be calibrated easily. That is the total, or if you want to be obscure "integrated", power within the receiver's bandwidth. It is also the power as used in an AGC system if it really keeps loudness more or less constant. Picking a single spectrum element can mess AGC systems, too.

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.

Whereinell do you get that notion? It has NO compatibility with how well you are receiving a signal, the Eb/N0 reading.

Per the definition established in IARU Region 1 Technical Recommendation R.1, "the metering system shall be based on quasi-peak detection". Notice the reference to "peak detection". There is no "average power" mentioned anywhere in the definition. A correctly designed S-meter by definition reports only the peak signal strength detected, nothing more and nothing less.

They are speaking time domain. You are speaking frequency domain. They are not the same thing.

As Simon has stated long ago, if anyone wants anything else reported (such as a "total power") he would be glad to look into that, as a separate meter. But his S-meter has always been in strict compliance with the published definition.

He is not compliant with that IARU definition. He has something sort of useful. It is NOT compliant.

Mark

{^_^}

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