[RTTY] Advise requested for RTTY Hardware

[Kok Chen]

On Aug 16, 2009, at 11:37 AM, Joe Subich, W4TV wrote:

> The only way to do FSK (as opposed to AFSK) with fldigi is
> using an envelope detector/driver as is done in USB Interface
> III (or as documented in the fldigi help files).


No, that is not the "only" way.  You can use fldigi in normal AFSK  
mode, and use K4DSP's FSK Regenerator:

http://k4dsp.homeip.net/~doug/regenerator/

It is however, not an appliance operator's box.  Some assembly and  
competency with a soldering iron is required (or use a solderless  
breadboard, as I had done when I was testing it :-).

You can indeed use Doug's regenerator with any AFSK software on any  
operating system.  *Anything* that puts out an AFSK tone pair,  
including all the old TNCs (in AFSK mode) will work.  With Doug's  
regenerator, there is no need for a special 1 kHz secondary keyed  
tone.  Just use the standard 2125/2295 AFSK tone pair on a single  
audio channel.

Simple as it is, the AVR firmware in Doug's circuit is not just an  
envelope detector, but the firmware includes a full fledged AFSK  
demodulator.  It does require a signal with good SNR, but a computer  
sound card output is more than clean enough for it.  It demodulates  
and slices the AFSK signal into an FSK signal (and while doing that,  
it also generates PTT).  It will also generate an independent CW  
keying signal for various Windows and Mac OS software that generates  
CW for J2A modulation by the rig.

73,
Chen, W7AY