On 06/10/2014 18:12, rickman wrote:
On 10/6/2014 12:38 PM, Peter Able wrote:
On 06/10/2014 16:43, rickman wrote:

building this. But there is only one problem with the idea. To use the
Si570 as the VFO for a receiver it would need to output a sine wave.
However the Si570 outputs square waves for digital circuitry. I don't
think the mixer would appreciate all the harmonics produced in a square
wave would it?

Then use a DDS.

There are lots of things you could do. I think Gareth got the idea
because the Si570 looked like it would be easy to use. But it just
doesn't fit the bill.

You posed a problem; I gave you an answer. BTW there cannot be an
easier item to lash to a microcontroller than a DDS

What frequency range would be of interest for tuning these older receivers?


Up to 30MHz?

Once I read up on the Huff and Puff modification, I like the idea. It
doesn't change the receiver really, it just keeps it on the correct
frequency by using the VFO as a VCVFO.

Huff-and-Puff is fine - but its weak point is that the oscillator being
controlled must drift by less than the Huff-and-Puff step in the
Huff-and-Puff update period.

Is it common to have a voltage
control on the VFO in these receivers? Or is that a mod that would have
to be made?


No, most applications of Huff-and-Puff have included the varicap diode
as part of the mod. Not a big issue - unless you want to keep the
receiver totally authentic.

This is really quite an interesting idea. I've DDS'ed some classic
sets. The change in performance was startling - and I had no problem
getting used to driving the set via a 4 by 4 keypad - but I can readily
appreciate that this proposed combination of the operational advantage
of the newer technology with the older style of user interface has real
charm.

PA