Hello Andy,

I just started from SNR (in dB) = 10*LOG(Psignal/Pnoise)
Or for SNR = 1 (0dB) ==> Psignal = Pnoise, thus RMSsignal = RMSnoise
If the signal is a sine (most obvious) then RMS of the signal = 0.707*Amplitude 
of the signal
If the noise is white (random function) then the RMS of the noise = 
0.577*Amplitude of the noise
So for 0dB SNR Amplitude of the noise = 1.225*(Amplitude of the signal)
As I sample at 11025Hz the total noise bandwidth is 5512Hz, and WSPR (what I 
took as a reference) takes noise over 2500Hz BW I compensated for that.
A bit to my own surprise by the first tests WSPR showed the same SNR as I 
intended to generate 
(+/-1dB).
As I intended to compare modes (not to make exact SNR measurement) I did not 
worry too much about how correct the produced SNR was. My first idea was to use 
that value as a start and then "fine tune" it with whatever WSPR came up with. 
But that seemed not nessecary.

Opera gives a 3-4dB offset for the SNR. maybe a noise bandwidth issue ?
5512Hz vs 2500Hz = 3.4dB ...


73,

Rik


________________________________________
Van: [email protected] [[email protected]] 
namens Andy Talbot [[email protected]]
Verzonden: donderdag 2 februari 2012 19:58
Aan: [email protected]
Onderwerp: Re: LF: QRSS3 "challenge"

I was going to make muttering noises about the S/N being dependent on
the QRSS speed, then realised   ..... duh....
it doesn't matter!

When normalised, -28dB always corresponds to 6dB above the noise bandwidth.
What effective bandwidth (ie noise bandwidth divided by FFT bin size)
have you assumed?
Hamming window is about two FFT bins, Blackman Harris three,
rectangular window is unity.

Andy
www.g4jnt.com


On 2 February 2012 17:17, Rik Strobbe <[email protected]> wrote:
> Dear all,
>
>
>
> as mentioned some days ago I generated a whole series of Opera, WSPR
> and QRSS3 audio with a known SNR.
>
> For Opera and WSPR it was easy to determine the lowest SNR for a proper
> decode. But for QRSS3 it is much more difficult as it depends on the
> operators "sharp eye". It must be somewhere in the range of -24 to -28dB SNR
> (@ 2.5kHz BW).
>
> Today I did put all the QRSS3 screenshots in this range in a
> website, where you can fill in what you see (decode) for each screenshot.
>
> I would like to invite all of you to give it a try and send me the results
> (the more entries the better the statistics).
>
> After some time (Feb 10th) will put all results into some nice tables
> and graphs and make them available.
>
> Of course no personal (individual) results will be published. But based on
> the results every participant (who keeps his results) can see where he ends.
>
>
>
> The "QRSS3 Challenge" can be found at http://on7yd.strobbe.eu/QRSS/
>
>
>
> 73, Rik  ON7YD - OR7T