Hi,
Is there any reason why the s-meter reading doesn't go below -140 dBm?
I
The signal in the picture above is at (appr) -145 dBm while the S-meter shows -140 dBm.
Or is there a setting that I can adjust to change the minimum value?
73's TooN
Minimum s-meter reading
Re: Minimum s-meter reading
The long of it:
You have, roughly, a 3 kHz bandwidth for the S-Meter. You have a signal a touch over -150 displayed and a noise level, per pixel, of maybe about 15 dB lower level. The 3 kHz bandwidth is about 300 pixels wide. If you add all the noise in that 3 kHz bandwidth you get 300 times the total noise. That would add 25 dB to the noise placing the "signal" 10 dB into the noise. Simon's S-Meter algorithm is sort of funky, and in my gentle opinion broken, so instead of reading something like -135 it is reading much lower.
The short of it:
You are reading total noise power in a bandwidth much larger than the signal.
Set the bandwidth down to 100 Hz and see what happens,
{^_^}
You have, roughly, a 3 kHz bandwidth for the S-Meter. You have a signal a touch over -150 displayed and a noise level, per pixel, of maybe about 15 dB lower level. The 3 kHz bandwidth is about 300 pixels wide. If you add all the noise in that 3 kHz bandwidth you get 300 times the total noise. That would add 25 dB to the noise placing the "signal" 10 dB into the noise. Simon's S-Meter algorithm is sort of funky, and in my gentle opinion broken, so instead of reading something like -135 it is reading much lower.
The short of it:
You are reading total noise power in a bandwidth much larger than the signal.
Set the bandwidth down to 100 Hz and see what happens,
{^_^}
- Simon G4ELI
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Re: Minimum s-meter reading
The reason: I designed the S-meter with a minimum value of -140 dBm.
Re: Minimum s-meter reading
Thanks for the clarification!
Re: Minimum s-meter reading
That is reasonable since -133 dBm is S0. {^_-}
Still, he has a 3 kHz bandwidth with the very narrow signal just barely over the noise. So I'd expect to see an S-Meter reading well above the signal peak on the spectrum report.
{^_^}
Still, he has a 3 kHz bandwidth with the very narrow signal just barely over the noise. So I'd expect to see an S-Meter reading well above the signal peak on the spectrum report.
{^_^}