[RTTY] FSK etal

[w1hkj]

On a recent posting, Mark, G0MGX wrote:
>
> You could, but that would only be AFSK i.e. the audio generated in the 
> computer and fed to the radio. The USB gives you an additional 
> computer soundcard (which happens to be in the radio rather than the 
> PC). For FSK you have to use the ACC for PTT and the RTTY port for the 
> FSK keying.
I think we need a way to distinguish FSK generated in the transceiver 
from a sideband audio FSK signal.  AFSK is really not the latter, 
particularly with a transceiver such as the Yaesu FTDX-3000 (or even my 
lowly FT-950).

2Tone, Cocoa-Modem, fldigi, and probably a few others produce RTTY audio 
signals that are a unique combination of both frequency and amplitude 
modulation.  This type of signal is narrower (more friendly to your 
contest neighbor) than a frequency shifted RTTY signal typically 
generated by vintage gear.  It also can reduce inter-symbol-interference 
in the received signal.  To my knowledge the K3 (and possibly the KX3) 
is the only transceiver that performs mark/space filtering.  I do not 
know the details of the design, but I would guess that this occurs 
immediately following signal generation.  In a modern DSP implemented 
transceiver this can be an integral part of the TTY digital signal 
processing algrorithm.

73, Dave, W1HKJ
fldigi developer