> But did he say (or is it possible) to lower the shift range, or is it
> more trouble than it's worth

Having spent some more time studying the circuit over the weekend I
now have a reasonable idea of the way it all works, and I suspect the
answer to your question is probably the latter - more trouble than
it's worth. Adjusting the oscillator to run at lower frequencies seems
feasible, but it brings a few other problems with it: there is a
considerable DC offset on the signal coming out of the oscillator, and
it depends on the control voltage (i.e. frequency) of the osc - at
it's lowest freq its about +2V, at the high freq end its about -2V.
This DC is blocked from the 1496 chips doing the main multiplications
by some capacitors - removing these to allow low frequencies through
would also allow the DC through, and this is likely to upset the whole
1496 set-up (which is pretty hard to figure out even *with* a 1496
datasheet..). Also the amplitude of the osc output appears to decrease
as frequency decreases, therefore there is likely to be a point where
it just stops oscillating reliably. Which is not to say that it is
impossible to lower the lowest shift frequency, just that it would be
non-trivial!

Tim

[The views expressed above are entirely those of the writer and do not
represent the views, policy or understanding of any other person or
official body.]