RadioBanter - anyone know about kit modifation to CW rigs for RTTY or other digital modes

In article . com,
an_old_friend wrote:

Back a long (pre 2000)while in Policy someone was tlaking about it
being easy to modify one the lowpower CW transceiver kits for some or
other digital modes

Anyone have some thoiught and info on this With Nocde HF comming I'd
love to build something that, either stand alone or laptop asisted

It shouldn't be difficult to modify a VFO-tuned CW transmitter to
transmit RTTY. You could do this with a varactor diode, in parallel
with the main tuning capacitor - drive the varactor with a two-state
variable voltage, to shift the transmit frequency the necessary number
of Hz.

If you have a VFO-tuned CW transceiver, which uses a varactor to
offset the transmit and receive frequencies by the appropriate
distance to generate a receive sidetone, then this transmit-offset
circuit could probably be modified pretty easily for dual-offset RTTY
operation.

You might need to retune your receiver bandpass filter to widen the
passband a bit... this would depend on the mode and the rig.

You might be able to do something similar to this with a
crystal-controlled QRP rig, but I suspect that pulling a crystal that
far with a varactor might be somewhat difficult.

This basic approach was, I believe, the preferred one for RTTY
transmission years ago, back before sideband rigs had good carrier and
opposite-sideband suppression. It can result in a cleaner RTTY signal
than you'd get if you use AFSK modulation into a sloppy sideband
transmitter.

Doing more-sophisticated digital modulations (e.g. PSK31) would
probably require starting with a sideband rig.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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