[MRCG] RTTY

[Mark J. Blair]

On Sep 27, 2014, at 10:19 , Jim Falls <radio-tuber at att.net> wrote:
> Thinking of the Sunday net with the 850 Hz offset. If I understand RTTY, one could have several other signals in there. All you need is the centerline frequency es offset to decode?

Correct. An ideal decoder would look at narrow bandwidths around the mark and space frequencies, and reject anything else. Performance will vary quite a bit between different real-world implementations, of course, and there are trade-offs involved in making the decoder more or less selective. I've gotten solid Clatternet copy in the presence of nearby jamming signals, even with jamming tones falling between the mark and space tones of the desired signal. There was even a recent case where two Clatternet stations doubled, but fldigi managed to keep copying one of them because the other was tuned just far enough off center for fldigi to be able to reject its tones.

Although I don't have experience with the PRC-47 and its FSK converter yet, I would expect it to be considerably less selective by design since it just allows tuning in 1 kHz steps and it would presumably be expected to interoperate with earlier VFO-based sets like the GRC-26 and GRC-26D that drift a lot more and have much less precise tuned frequency indications. It takes some skill and attention to keep a T-368 or T-195 right on the correct frequency, so anything expected to interoperate with them should naturally make some allowance for sloppy tuning.


-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/