-24 is not the minimum SNR reported. -30 is. Below -24 is pretty rare though
and is a big "knee"in the data.Here's a histogram from my station.Mike W9MDB
3 -27 23 -26 75 -25 2353 -24 3907 -23 8187 -22 16812 -21
28821 -20 41617 -19 49679 -18 54327 -17 56758 -16 56976 -15 55953 -14
54478 -13 52240 -12 50195 -11 47384 -10 44725 -9 42112 -8 38922 -7
36171 -6 33457 -5 30718 -4 28010 -3 25648 -2 23303 -1 21015 0
18789 1
16493 2 14505 3 12637 4 10915 5 9340 6 8041 7 6784 8
5697 9 4804 10 3982 11 3401 12 2743 13 2229 14 1724 15
1380 16 1051 17 796 18 606 19 433 20 313 21 244 22
173 23 110 24 75 25 48 26 38 27 30 28 26 29
13 30 8 31 10 32 1 33 2 34 1 35 2 36 12
38 2 39 5 40 1 42 1 43 1 45 1 47 1
48 1 49 1 52 1 57 1 58 1 59 1 60 1 61
2 62 1 63 2 64
On Monday, April 10, 2023 at 08:44:23 AM CDT, Reino Talarmo via wsjt-devel
<[email protected]> wrote:
Hi Sam,
Thanks Sam, I am aware of that problem and for sure it affects to the
"absolute" S/N values. There is another issue due to the limited dynamic range
and that all S/N values below -24 dB are reported as -24 dB. I have partially
tried to avoid the issue by only taking into calculation messages that are
received by both receives. I also checked how much those measurements with one
of the values reported as -24 dB (less than 1 % of all values) really affect to
the calculated average and deviation values and there is a minor shift at one
or two higher attenuation point, when I leave those out.
73, Reino OH3mA
-----Original Message-----
From: Sam W2JDB via wsjt-devel [mailto:[email protected]]
Sent: maanantai 10. huhtikuuta 2023 14.38
To: [email protected]
Cc: Sam W2JDB <[email protected]>
Subject: Re: [wsjt-devel] Truncated Waterfall Display "Feature"
Hi Reino,
The one thing to be aware of when analyzing SNR is that since you can not
account for the signals that you did not decode,
those that are below the threshold, the mean will always be biased towards the
positive side and those missing decodes
invariable would have affected the variance and standard deviation values.
73,
Sam W2JDB
-----Original Message-----
From: Reino Talarmo via wsjt-devel <[email protected]>
To: 'WSJT software development' <[email protected]>
Cc: Reino Talarmo <[email protected]>
Sent: Mon, Apr 10, 2023 3:33 am
Subject: Re: [wsjt-devel] Truncated Waterfall Display "Feature"
Hi,
Just as promised, I looked what happens, when I set waterfall from 200 Hz to
1500 Hz (just bit more). The measurement was a side result of a study how a
narrower radio filter affects to the S/N values. I have two similar receivers
and I feed the same antenna signal via a power divider to those receivers. I
calculate using ALL.txt files differences of the S/N values for the same
(common) messages. That removes transmit power and propagation from the
equation. For the filtering study I calculate in 25 Hz slots the number of
messages and an average and standard deviation of S/N differences. By this
method the filter passband and out of band attenuation on quite wide range up
to 60 dB on longer measurement times. The typical standard deviation is about 3
dB. Quite good for a S/N calculation that is not designed at all for this
purpose. Also linearity seems to be better that in some earlier versions.
Now the result: there is not a single decoding in 35 361 decoded messages above
1500 Hz.
A related observation close to the waterfall edge. The standard deviation
increases from 3.8 dB to 7.7 dB in the last 25 Hz slot. The increase starts at
1425 Hz slot. There is also 4.6 dB gain increase over that range. So there is
some S/N calculation anomaly close to the band edge and unnatural high S/N
values are seen close to band edge.
Of course there is also the natural calculated S/N increase over the narrow
passband due to missing noise outside the passband. That easily results to
misinterpretation that a narrow RX bandwidth will enhance decoding probability,
it is just the actual "wrong" noise bandwidth in the S/N calculation!
73, Reino OH3mA
>From: Reino Talarmo [mailto:[email protected]]
Sent: lauantai 8. huhtikuuta 2023 10.46
>Hi All,
>You may discuss different issues! In FT8 mode Sam is correct as the signals
>are reached only on the frequencies displayed on the waterfall. In JT65 and
>Q65 the situation is different at there is a spinner called F Tol that defines
>the search range independent of the waterfall range. All that is written in
>the User Guide. If something else is happening, then it is extra for the
>operator benefit! I’ll do a FT8 test in my next 24 h recording.
73, Reino OH3mA
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