Ekki Plicht wrote:
>
> > For those fsk purists, Yaesu uses keyed afsk not fsk.
>
> What is keyed AFSK in contrast to AFSK and FSK? Never heard the term.
Well, even though I didn't originate the original post, let me try and
explain...
Your TNC (or whatever type of rtty modem you use), can output TWO types
of transmit signal towards the radio: a DC voltage that varies between
mark and space, usually called "FSK" and audio tones, called "AFSK".
The difference comes in at the radio, where the signals described above
can be processed by your radio in THREE different manners (although most
radios do not have all three modes).
If the radio takes the DC signal from above and uses it to DIRECTLY
shift the VFO or synthesizer or whatever (usually with a varicap diode),
this is what I call "true" FSK (for the purists). If the radio takes the
audio tones and puts them into the microphone plug or equivalent (phone
patch input or whatever), this type of operation is "AFSK".
The third type, what was referred to as "keyed AFSK", uses the DC signal
from the modem to key an INTERNAL afsk tone generator inside the radio,
really ending up with AFSK after all. So, even though you are sending
only a varying DC signal to the radio, the radio internally converts it
to AFSK, rather than using the DC signal to directly shift the
frequency.
Hope this clarifies it.
73/Carter/K8VT
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