Only reason to narrow BW is reduce the voltage into the ADC if it is over driven by broadband noise or an undesired signal. Attenuation may help but at the loss of dynamic range. DE N2LO~>
Sent from Xfinity Connect Application -----Original Message----- From: [email protected] To: [email protected] Sent: 2018-10-19 11:08:40 AM Subject: Re: [wsjt-devel] Improving S/N Hi Frank, On 10/19/2018 9:47 AM, Frank Kirschner KF6E wrote: > One thing I haven't seen discussed on this reflector is improving the > S/N by narrowing the receiver bandwidth. It is no surprise that > decreasing the bandwidth received increases the S/N, by 10 to 15 dB, > sometimes more. When I see a station I want calling at -24 or so, I can > narrow the BW and get solid communications. This is very easy with the > graphical presentation and digital filtering of the Flex 6600, but with > a little practice, could be done on any modern receiver. > > This means that, if we knew where the stations were calling at -30 or > so, we could focus on them and bring them up to the point of making > contact. Since you can't decode stations at that S/N, it would have to > be done "out of band." Is there any thought being given to setting up an > FT8-only DX cluster with exact frequencies? > > What a fascinating hobby! Desirable settings for received bandwidth are discussed in the WSJT-X User Guide here: http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-1.9.1.html#TRANSCEIVER There is NO decoding advantage to setting a narrow received bandwidth, (for example, 500 or even 200 Hz) centered on a desired weak signal. Why not? Because the WSJT-X decoders already filter the data in software, down to a detection bandwidth equal to the keying rate (6.25 Hz for FT8, 2.69 Hz for JT65, 1.74 Hz for JT9, etc. A narrow receiver bandpass setting will only serve to confuse the decoder and bias its measurement of S/N, producing unreliable values. -- 73, Joe, K1JT _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
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