On Sun, 5 Oct 2014, rickman wrote:

On 10/5/2014 3:15 PM, Radiohead70 wrote:
On Sun, 05 Oct 2014 19:30:43 +0100, gareth wrote:

Being somewhat of a polymath (just spent all day fence judging at a
horse trial) I find that I have a string of ideas faster than I could
ever implement them (rather unkindly described in one area as
vapourware), but I think it to be useful to punt them for a wider
discussion.

Musing upon the Huff-and-Puff technique, I wondered if there was a
better way to improve the frequency stability of older RXs,
because the Huff-and-Puff necessarily brings about a punctuated
frequency span (eg, multiples of 32 Hz), and this is what I came up with
...

Using the ubiquitous timers to be found en masse in most micros that
seem to sell for only a few pence / cents these days, implement a
frequency counter to measure the local oscillator. Then, when the user
presses a Lock button (yet to be provided) the same micro can program an
si570 to generate the same frequency indefinitely and to switch the
mixer stage from the original to this new oscillator.

If you are going to go to those lengths, why not program the micro to
recognise the difference between rapid changes of frequency (tuning) and
slower changes (drift) and apply a correctional voltage to a varactor in
the case of the latter. Capture range may be a problem if the radio is a
determined drifter.

I'm not sure I understand the issue. But if you want a digitally controlled
oscillator for your mixer why not just make a digitally controlled oscillator
for your mixer? That is already there with the Si570. Why the complex usage
of using the existing oscillator and then switching?

He wants a big Eddystone dial, likely connected to a Command Set or BC221
variable capacitor.

Michael