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SDRUno S-Meter Reading?

Posted: Sun Jul 15, 2018 4:42 pm
by n3hkn
First I assume that the data for the meter is picked up close to where the audio is handed off to the PC. I really am not an engineer but an amateur customer. When I vary the audio bandwidth the reading on the S-Meter changes. Very strange. Some Hams may believe that it is true signal strength when it is really a measure of what they hear (or see - SSTV). As such the reading is not an engineering value but a perception measure. We are hopefully taught to think of signal-to-noise ratio. Grab the RF gain not Audio gain. Once you allow the AGC to do its thing it will smooth out the signal and suppress some of the intelligence carried by the signal. Inflections from the speakers voice are compromised. Perhaps that is why some radios sound so flat. So the S-meter can also be fooled with a measurement that really does not reflect the real readability of the signal. Grab the S-Meter signal data outside of the AGC calculation. I wonder if some radios just grab the smoothed AGC data and display is as a signal strength.

Lots of differences and perhaps the Governing Body, The ARRL, should develop some standards otherwise we simply go down another fictional path similar to the contest 59 rule.

Re: SDRUno S-Meter Reading?

Posted: Sun Jul 15, 2018 7:02 pm
by glovisol
Sorry to contradict, but the S meter reading, in SDRplay devices, is tied to the system metered RF input in dBm, according to the universally known "S" rule. In fact, if you watch closely, the S meter indication DOES NOT vary with audio filter bandwith. It varies with input RF intensity, which of course changes with speech modulation in SSB. As a matter of fact, the dBm values shown have been checked by others and by myself (I used a spetrum analyser) and they are accurate to 1 dB or better.

Re: SDRUno S-Meter Reading?

Posted: Mon Jul 16, 2018 9:06 pm
by MikeHarding
Another vote of confidence in my RSP1A 'S' meter. I used my professional signal generator to check it and found it accurate to better than 1dBm up to 500MHz, above that the losses in my measurement setup take over but further checks up to 1.2GHz suggest it's probably still correct. This makes an interesting contrast with my Icom IC-7300 which is always inaccurate below S9 in some instances by up to four (yes 4) 'S' points! The designers have done an excellent job with the RSP1A 'S' meter, sufficiently so it makes the unit a decent poor man's spectrum analyser.