Mike,
Glad to help and glad it made sense!
When you tune across an RTTY signal using your 400 Hz filter with the
dual passband filter turned off, first one shift, either Mark or Space
depending on the direction you are tuning, will enter the passband of
the filter and then both shifts. Assuming you have the Shift control on
the front of the K3 centered, when the Mark and Space energy is centered
on either side of the center of the filter (and the decoder), the RTTY
will decode properly. Besides seeing the decoded text, the CWT
indicator in the meter area of the K3 display will show you when you
have the Mark and Space energy centered for proper decode. As you
continue to tune same direction, you will lose the first shift you
acquired as it passes out of the other side of the filter passband, and
then finally you will lose the other shift as you continue to tune away.
73,
Bill - NA5DX
On 2/19/2016 10:06 AM, Mike Murray wrote:
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
<mailto: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 <mailto:w0agm...@gmail.com>>
To: "Wes (N7WS)"<w...@triconet.org <mailto:w...@triconet.org>>
Cc:elecraft@mailman.qth.net <mailto:cc%3aelecr...@mailman.qth.net>
Subject: Re: [Elecraft] K3 - AFSK anamoly? No replies, try again
Message-ID:
<CAP7zeEJBvJCVEY-=uu21OQTN=eavupuy_wf-lwz5_qoameh...@mail.gmail.com
<mailto: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
