Hi David,
Welcome to this list!
On 8/25/2017 9:20 AM, David Alloza wrote:
I would like to know how you evaluate the noise level used for the SNR
calculation, it seems to me that there are two ways to do it:
1> You take the average spectral power present in the spectrum received (on
2.4Khz bandwidth) , and you compare to the power of the station received.
It's simple, but the presence of several powerful stations will change the
result.
2> or you are trying to evaluate the background noise level in the spectrum
of 2.4Khz by hide the influence of the stations received, and in this case
how is this evaluation done?
SNR calculations are done in somewhat different ways for each of the
WSJT-X modes, but all are intended to be a close approximation to your
#2. Briefly stated, we fit a "baseline" to the spectral regions in the
Rx passband that do not contain signals. The spectral density of noise
close to a signal's frequency is evaluated from this baseline. This
value is scaled up to 2500 Hz bandwidth, and becomes the denominator in
the S/N calculation.
For interest: at present, calculation of SNR in the new FT8 mode comes
close to the above ideal only for signals *in the clear*. SNRs for
signals with nearby interference are effectively evaluated as
Signal/(noise + interference)
We'll do a better job in an upcoming release.
-- 73, Joe, K1JT.
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