[RTTY] RTTY from DX

[Kok Chen]

This URL has a link to a Quicktime movie of VP2MUM RTTY operation that Tom, DL2RUM has posted:

http://groups.yahoo.com/group/cocoamodem/message/509

Give it a while for the file to load and start running as a movie.  

Tom mentioned in email to me (he is still at VP2M for another day) that he is primarily the CW op for the expedition, but had fired up his RUMped software on RTTY just to see how it plays, and had made only 200 RTTY QSOs.  Tom uses RTTY, but is not as mad dog about it as some of us are :-).

RUMped's window is at the right bottom of the Mac notebook's screen.  RUMped is Tom's free DXpedition/contest program for the Mac OS X, which he had written in REALbasic.

RUMped uses the headless version of cocoaModem as the RTTY/PSK31 modem, and using MySQL as the underlying database.  

In the headless mode of cocoaModem, everything is passed between the two programs through AppleScript; even the waterfall scan lines are computed and passed from cocoaModem to RUMped using AppleScripts.  

Having everything in a single RUMped window avoids the problem of the "window focus" problem when clicking on windows in multiple programs.  The crossed banana at the bottom left of the screen (which consumes more processor cycles than the waterfall) display is drawn from cocoaModem since you never have to click on it.

I have mentioned the "click buffer" that Tom alluded to in the yahoo group, before on this reflector.  It allows you to click on a station even after it has stopped transmitting.  The "tape loop" goes back about 20 seconds into the past.  Tom tells me that he typically clicks halfway in the waterfall, giving him about 10 seconds of playback.  The playback re-runs at many times real time and catches up to realtime in a short time.

You can see a few times where Tom had clicked on a station after it had already stopped transmitting or about to stop transmitting, but recovered the callsign nevertheless.  This probably is unnerving on the receive end to see yourself called a second or two after you have stopped calling :-).  You can tell from this movie that it is not because Tom is slow, but because he had been clicking around for a callsign :-).

Somewhere in the movie, you can see two stations of about equal strength that overlaps almost exactly 85 Hz in the waterfall and Tom had pulled one of them effortlessly.  The K3's I.F. filter was opened up to the full 2 kc passband of cocoaModem, and the narrow demodulation filter is inside cocoaModem itself.The demodulator was seeing only three tones in this case, two from the desired signal and QRM that is centered in between the actual tones -- the QRM is close enough to be centered and thus present no bias to the ATC slicer.

Some photos are already posted here

> http://dl2rum.de/dl2rum/Photos_VP2M.html

73
Chen, W7AY