Thanks for comments Reino and Andy. My 20 dB degradation number was based on an actual measurement using FM mode on my radio. Basically injected a signal into the antenna feedline which was terminated with a 50 ohm load. Measured the receiver quieting sensitivity, then repeated the measurement with the antenna connected in place of the 50 ohm load. Noted the difference in input signal level required to produce a given amount of quieting. Although the receiver bandwidth is different, if we assume the noise is uniformly distributed over frequency the bandwidth difference should not affect the difference measurement.
Think I’m going to redo that measurement using an actual locally generated FT8 signal as soon as I figure out how to get enough attenuation on the FT8 signal and keep leakage from spoiling the measurement. I don’t care about the SNR numbers reported, want to see if I can improve decoding sensitivity with additional filtering. Suffering from the frustration of others around me decoding stuff I don’t! From: Reino Talarmo via wsjt-devel <wsjt-devel@lists.sourceforge.net> Sent: Sunday, December 10, 2023 10:19 AM To: 'WSJT software development' <wsjt-devel@lists.sourceforge.net> Cc: Reino Talarmo <reino.tala...@kolumbus.fi> Subject: Re: [wsjt-devel] WSJT noise estimates Hi Andy, Interesting approach. But how you know that it really enhanced the signal detection? The wanted signal is now close the wanted signal and that may disturb the S/N calculation and you will see a better S/N values with your method without a real better sensitivity. Possibly the only real comparison could be with two radios fed from the same antenna with a power divider (you may need a an amplifier before the power divider for compensating attenuation) and two instances of wsjt-x. Then a statistical study of success/failure rates could tell a real story. Just my two pennies. 73, Reino OH3mA From: Andrew Neumeier via wsjt-devel [ <mailto:wsjt-devel@lists.sourceforge.net> mailto:wsjt-devel@lists.sourceforge.net] Sent: Sunday, December 10, 2023 3:40 PM To: w0fy--- via wsjt-devel < <mailto:wsjt-devel@lists.sourceforge.net> wsjt-devel@lists.sourceforge.net> Cc: Andrew Neumeier < <mailto:ka2...@yahoo.com> ka2...@yahoo.com> Subject: Re: [wsjt-devel] WSJT noise estimates Joe, Just a comment here. I use FT8 frequently and almost always on 2 meters. My interest is in weak signals. I use a Omni VII here, with a transverter. I have had some luck using my notch filter on very weak FT8 signals. Setting the notch width at about 75hz, I have been using the edge of the filter to enhance the signals I am looking for. So, the notch is not directly on the desired signal, but set a few hundred hertz from it, usually below it. Of course, placing the notch directly on the signal would erase it, but I don't use it that way. I have worked a number of stations this way. It took some playing around to get this to work, and it does not always work, and one must see the signal first and have a decode failure, before turning to this remedy. Just my two cents. Best of luck, 73, Andy, ka2uqw On Saturday, December 9, 2023 at 10:05:26 PM EST, w0fy--- via wsjt-devel < <mailto:wsjt-devel@lists.sourceforge.net> wsjt-devel@lists.sourceforge.net> wrote: Been wondering how WSJT-X generates the noise power estimate it uses to calculate SNR for each FT8 signal. Does it simply collect all the signals and noise over the bandwidth selected on the waterfall and call that the noise power level or does it take a quick snapshot of the background noise level during the brief quiet period at the end of each 15 second FT8 sequence? Or is it more complicated than that? I am plagued with a S2 -S3 noise level on 6 meters nearly all the time that if not AWGN is pretty close to it. 10 meters is even worse. The DSP noise blanker in my TS590 will reduce it slightly. I estimate this is degrading my ability to decode FT8 signals on 6 by nearly 20 dB compared to the noise level generated by a 50 ohm resistor. I don’t use an LNA ahead of the radio – would be pointless. I don’t use the noise reduction feature in the radio either as it tends to lose very weak signals completely. Wondering if I can use the DSP in my TS590 to narrow the receiver bandwidth to perhaps 300 -500 Hz around a known offset to help pick weak signals out of the noise? I realize that the WSJT program filters the audio into much narrower BW bins so all the receiver filtering can do is reduce the receiver gain reduction caused by the noise pumping up the AGC but that might be beneficial. Likewise, would using the DSP notch to suppress a single strong local signal or birdie help since strong signals also reduce receiver gain? Should I deselect the flatness option if I use these tools? Would narrowing the waterfall span help any since the program ignores anything outside that span? Would appreciate any insight you can share. Joe W0FY _______________________________________________ wsjt-devel mailing list <mailto:wsjt-devel@lists.sourceforge.net> wsjt-devel@lists.sourceforge.net <https://lists.sourceforge.net/lists/listinfo/wsjt-devel> https://lists.sourceforge.net/lists/listinfo/wsjt-devel
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