RE: [RTTY] Distortion

[Jerry Flanders <jeflanders@comcast.net>]

At 11:29 8/25/04, VE3XD wrote:
> ... the Yaesu rigs are really generating AFSK was
> interesting and maybe confirms my opinion that the switch to FSK is not as
> important as I once thought.

Yaesu is not simply using AFSK - that is not the correct way to think of 
it. Yaesu rigs are simply adding one more heterodyne conversion to their 
internal processing to get the signal on the air.

The frequency of generation of the original RTTY signal inside the rig 
doesn't matter. All modern rigs generate the original RTTY signal at one 
frequency, then convert it in one or multiple stages to the final 
transmitter frequency. Some rigs do it at one intermediate frequency, some 
at another. My FT1000D does it at 2125/2295 Hz, and my 756PRO does it 
around 36 KHz (IIRC). As long as the engineering is done correctly and the 
rig isn't defective, you can't tell the difference at the receiving end. An 
external amp doesn't even need to be linear!

The major difference between what hams call AFSK and what Yaesu does in 
their rigs is that Yaesu has engineered their rig to up-convert cleanly 
this way, as opposed to the usual AFSK system where the guy in the shack 
does all the setup and adjustments to get the signal on the air. Some of us 
can do it properly, but many apparently can not.

Jerry W4UK

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