Hi Nick, Bill, & All - Bill Somerville <g4wjs@...> writes:
> > On 08/11/2014 11:35, nick wrote:of BFO > > Hi Nick & All, > > I like the empirical approach Paul! Thanks, Nick! > > > > Your results pretty much correspond with my observations. > > > > The softrock and sdr-core combination goes all the way down to 0Hz. I > > run the softrock LO with a 12kHz offset to get away from DC and the LF > > limit of the Delta 44 sound card. > > > > I will start logging at < 250Hz and see what happens. > You might try tuning up to ..078.5 (e.g. 14.0785 MHz) and running JT9 > for these tests. I suggest it due to the bandwidth of the signal being a > much smaller proportion of the audio frequency range you want to test. > That way you will get a much better indication of the lower limit. > Having said that, in both cases (JT65 & JT9) the sync tone is at the LF > end of the signal and detection of that is fundamental to decoding. > > Joe K1JT will have a definitive answer, but I wonder if the DF is in any > way proportional to the resolving capability of the WSJT-X decoders. If > not then there is no theoretical lower limit and any limiting effects > would be down to secondary factors like roll off in SSB demodulator and > any audio circuits and of course the obvious filtering of the BFO. Have performed a little off-the-air testing, using recorded JT-65 signals synthesized down in frequency via another app, and employing just the laptop and the SignaLink USB Sound Card. Results were reproducible; was able to decode down into the single digit region, as far as the app could differentiate the audio freq. So, I guess "no theoretical lower limit" is holding its own. I agree with Bill that limiting appears to be chiefly resulting from secondary factors, to which one must add atmospheric and man-made noise when decoding live on-air. Best to tune away. > There is another issue to consider, if you transmit very near your Rx DF > zero you may get a reply below your DF zero which you will not decode so > working near DF zero is not necessarily a good idea. Via on-air monitoring, users noted transmitting very near their DF zero (not tuning away) often generate phantom/spurious signals in addition to the intended signal. This includes both an image mirroring the intended signal to which others respond in vain, and an image that is "double- spaced" in bandwidth. Chats via JTAlert-X text messaging confirmed the practice employed by some. (Users employing speech processing generate a whole different set of QMR!). > > > > 73 > > > > Nick G3VNC > 73 > Bill > G4WJS. > > > > On 08/11/14 07:36, Paul DU2/WA8UGN wrote: > >> Paul DU2/WA8UGN <keatipa <at> ...> writes: > >>> I have had WSJT-X v1.4.0-rc2 (beta) decode a JT-65 signal at 183Hz on Nov > >>> 7, 2014: > >>> > >>> 1607 -23 -0.5 183 # UK8OAR DG5SAY R-20 > >>> > >>> 1609 -22 -0.5 183 # UK8OAR DG5SAY 73 > >>> > >>> 73 > >>> > >>> Paul DU2/WA8UGN > >>> > >>> ---------------------------------------------------------------------- ---- > >> ---- > >> Follow-up information: > >> > >> Date/Time: 11/7/2014 1607-1609 UTC > >> Frequency: 14.076183MHz > >> Low-end audio cutoff (-3dB): ~300Hz > >> Low-end audio cutoff (total: ~120Hz > >> Equipment: Kenwood TS-570D > >> SignaLink USB Sound Card > >> Sony VAIO VPCCB laptop > >> > >> Cheers & 73, > >> > >> Paul DU2/WA8UGN (formerly G5BNV) > > > > ------------------------------------------------------------------------ ------ > > _______________________________________________ > > wsjt-devel mailing list > > wsjt-devel@... > > https://lists.sourceforge.net/lists/listinfo/wsjt-devel > > -------------------------------------------------------------------------- ---- > Best 73 Paul DU2/WA8UGN ------------------------------------------------------------------------------ _______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
