[Collins] AOR DDS-2A Revisited

[Adam Farson]

Hi Sheldon,

What I was alluding to is that as has been the case for many decades in the
radio-communications industry, we amateurs are the beneficiaries of
technological advances driven by the requirements of other radio services.
For the purposes of this topic, frequency synthesis and channelisation have
trivialised the task of tuning a voice SSB signal correctly at the receiver.

Modern, synthesised amateur transceivers are channelised for all intents and
purposes - even if the step size is 10 or 1 Hz. It has been my experience
that if the master oscillators at both stations have been calibrated against
WWV (or CHU), the recovered audio will "sound right" if both synthesisers
are set to the same frequency. If one of the master oscillators is out of
cal, the other station can adjust RIT until the recovered audio "sounds
right". For me, a subjective impression that the voice pitch sounds
"natural" is an acceptable criterion. In my early amateur-radio career, with
a free-running VFO, this was exactly how I tuned in a J3E signal.

In current DDS-equipped amateur HF transceivers with a 1 Hz minimum step
size, the RIT increment is also 1 Hz. One generation earlier, PLL-based
transceivers with a 10 Hz tuning step also had a 10 Hz increment. The reason
for this is that the radio's CPU translates input from the RIT control into
a change in the synthesiser frequency-setting data value,  which is applied
only in receive mode.

Your description of R3E during Selcall transmission is fascinating. That is
a neat way of ensuring that the receiver resolves the tones at the correct
frequency.

Cheers for now, 73,
Adam VA7OJ/AB4OJ