Bill, Excellent analysis and I suspect you are correct in exposing my current, very limited knowledge of RTTY signals. Now that I think about the problem, it makes sense that the radio is doing exactly what it is supposed to when I hear the inverted tones 170 Hz down from the original signal. Rich, VE3KI, suggested turning off the dual passband filter to see if that has any affect, so I'll try that in the near future. Thanks for the response and ongoing RTTY lessons!
Mike - W0AG On Fri, Feb 19, 2016 at 8:22 AM, Bill Breeden <breede...@cableone.net> wrote: > Mike, > > What I see in your video is that you have the RTTY signal properly tuned > at 14,091.883. "Properly tuned" means that you have the Mark energy and > the Space properly aligned in the dual passband filter and the data > conveyed by the mark and space energy is being decoded and displayed. In a > normal "ham radio" RTTY signal the RF energy for the Mark and Space is 170 > Hz apart, with the Mark frequency 170 Hz higher, in RF terms, than the > Space frequency. When demodulated by a receiver operating in Lower > Sideband (LSB) mode, this results in two audio tones, with the audio tone > representing the Space energy 170 Hz higher than the audio tone > representing the Mark energy. In the video, when your radio is tuned to > 14,091.883, the tone representing the Mark energy is passing through the > "Mark" side of the dual passband filter and the tone representing the Space > energy is passing through the "Space" side of the dual passband filter, and > the RTTY data is decoded properly. When you tune down to 14,091.720 in the > video, a 163 Hz difference, you have the tone representing the Space energy > passing through the "Mark" side of the dual passband filter and the tone > representing the Space energy is outside of either portion of the dual > passband filter. There is no anomaly revealed in your video, that's just > the way that RTTY, the receiver, and the dual passband filter works when > you tune away from a properly tuned RTTY signal. > > The reason the data on the Space tone sounds like an inverted version of > the data on the Mark tone is because that is exactly what it is. In an > RTTY signal, the same data is carried by the both the Mark and Space energy > and the state of one is the inverted state of the other. > > 73, > > Bill - NA5DX > > > Message: 23 > Date: Thu, 18 Feb 2016 09:56:06 -0700 > From: Mike Murray<w0agm...@gmail.com> > To: "Wes (N7WS)"<w...@triconet.org> > Cc:elecraft@mailman.qth.net > Subject: Re: [Elecraft] K3 - AFSK anamoly? No replies, try again > Message-ID: > <CAP7zeEJBvJCVEY-=uu21OQTN=eavupuy_wf-lwz5_qoameh...@mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > After doing some more testing in last weekends RTTY contest, it appears > that I made an erroneous statement as to what I was hearing and where. > What I found is that as I tune down in frequency and find a signal that > will decode, if I then tune down another 170 Hz I'll hear the inverted > signal. Still using dual passband DSP filter at 400 Hz and 400 Hz, 8 pole > roofing filter as before. I have a brief video on uTube showing the effect > at: > > *http://tinyurl.com/hxykq9c <http://tinyurl.com/hxykq9c>* > > Anyone have additional thoughts as to what's causing this or where I should > look next? > > Mike - W0AG > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
