[RTTY] CWSkimmer use in Rtty

[Kok Chen]

On Jul 26, 2011, at 12:47 PM, Terry Dunlap wrote:

> Does it take two sound cards to use CWSkimmer and MMTTY (or whatever 
> you're using for RTTY)?

To receive both DX and pileup concurrently, you just need a single stereo sound card and one program, if you have the right program.

See here:

http://www.w7ay.net/site/Applications/cocoaModem/UsersManual/RTTYPage/WidebandRTTY/WidebandRTTY.html#widebandrx

If you scroll down to the first Figure (called Figure 11 because this page was cut from a much larger earlier page :-) you will see a window with two identical receive section that share a single transmit interface.

Further down, in Figure 12, you can see what one active receiver section looks like.

In cocoaModem, either modem can select any sound card.  The two receive sections can actually look at the same passband (i.e., to decode two different signals within the same 2.4 kHz passband) by selecting the same sound card.  Or, one receiver can watch the left channel of a sound card and the other receiver watching the right channel of a sound card.  Or, the two receivers can be connected to two completely different sound card with different sampling rates.

Each receiver has its own waterfall and its own crossed ellipse indicator.

(A little further down from figure 12, there is a short description of the RTTY click buffer.)

Regarding crossed ellipse displays, the non-waterfall mode in cocoaModem has a much fatter crossed bananas.  See 

http://www.w7ay.net/site/Applications/cocoaModem/UsersManual/RTTYPage/BasicRTTY/BasicRTTY.html#basictuning

Since the non-waterfall version assumes that you tune using the VFO knob, the wide bananas' bandwidth is much better at telling you which direction to tune when you are off tuned by a lot when you start.

With a waterfall, you can click quite closely to start with and the crossed bananas really only serves the purpose to fine tuning (cocoaModem uses the mouse scroll wheel or the Griffin PowerMate knob to fine tune).  Precise tuning helps with the really weak signals.

Anyway, cocoaModem is just a fun project that I started many years ago to play with digital modes.  Before the two waterfall demodulator, cocoaModem had the "dual RTTY" demodulator shown here:

http://www.w7ay.net/site/Applications/cocoaModem/UsersManual/RTTYPage/DualRTTY/DualRTTY.html

In that case, there is only a single "panadapter" which you can switch between the "main" or "sub" receiver sound card.  It is OK most of the time since the DX seldom QSY.  But the first two Ducie RTTY operations where the same JA op kept moving had caused me to think that I need an interface where you can watch both receiver's spectrum.  Waterfall tuning really shines when the DX keeps moving.  You can find him even before the VFO twiddler even notices that the DX has not issued a CQ for some time :-).

(I am sure many RTTY folks would rather forget the Ducie fiascos.  It even led our usually gentlemanly AA5AU to mock the operation with a web page -- was it Parody Island or something like that?   Newer RTTY ops missed out on the barrel full of chuckles we all had here.  :-)

There are other cases of unintended QSY, like when Trey N5KO was operating from Thule or South Georgia, I think (over heating rig, if memory serves).  Like being able to quickly switch from 45.45 baud to 50 baud, you won't need it to worry about QSYing DX too often.  But when you need it, you really need it, as many who tried to work P5/4L4FN found out.  Ed really cleared the spectrum for the peanut whistles to get through when he switched over to 50 baud :-).

73
Chen, W7AY