[RTTY] The Problem with AFSK ...

[Kok Chen]

On Jan 19, 2013, at 3:33 PM, Paul wrote:

> Does anyone know if the FT-1000D is true FSK or is it AFSK?

Keyed AFSK.    Not Direct FSK.

Look for a switch-tail ring counter with a set of resistors that has the weight of a sine table :-).  That is the way it appears in the FT-990 schematics.  The rig clocks the ring counter at different clock frequencies to produce Mark and Space tones, and very conveniently, the resistor weights produce a phase continuous audio sine wave output.  They change the clock frequency to get the different tone pairs (low tone, 2125/2295, etc).  Actually quite cleaver of Yaesu engineers.

The follow up FT-1000MP is Direct FSK (using direct digital synthesis VFO).

73
Chen, W7AY