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
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