On Thu, 4 Sep 2008, Ian Jackson wrote:

In message , Registered User
writes
On Wed, 3 Sep 2008 14:54:17 -0400, Michael Black wrote:

On Wed, 3 Sep 2008, raypsi wrote:

Hey Gary,

Rocks aren't cheap he http://www.icmfg.com/thruhole_crystals.html
Maybe in 9 land they pave the streets with gold.
Personally I'd go with a programmable divider or PLL.

Maybe you like retro, then I'd get some old rocks the ones
you can take apart and grind them down to git's the freq's you need.

And you can't grind them unless they are quite close to the desired
frequency. Grinding by hand will be too uneven, so the crystal will
stop working if you try to grind it more than a tiny bit.

My personal experience is an FT-243 crystal's frequency can be
increased by several hundred kilohertz through grinding. A more
abrasive media is needed for the slurry than scouring powder can
provide. Permatex 34A valve grinding compound works FB. Most of my 80M
rocks (26 between 3.5 & 3.6 MHz) were originally cut for 3237 kHz.
Many of my 40M crystals were moved several hundred kHz as well.

The key to grinding is not to try doing too much at once. Let the
abrasive do the cutting, no downward pressure is need from the
fingers..

It also relies on a big stock of crystals spread around so you can
find one sufficiently close enough, something that did seem possible
in the years after WWII, but after all this time attrition may have
reduced the stock considerably.

There are still a lot of them out there and they can be most
inexpensive if the actual frequency isn't too important.

73 de n4jvp

All this discussion about crystal grinding is very interesting. From my far
distant experiences, it is indeed a work of art and, more often, an act of
God. If the OP goes down that route, he may never actually get his receiver
built!

Looking at the websites of various manufacturers/suppliers (Google on
"crystal+frequency" and similar), it looks like you should be able to get
custom-made crystals in the required frequency range for less than $20 each.
I'm sure that at least the 5MHz will be available off-the-shelf for less than
$5 so we're talking maybe $100 for the six crystals.

The alternative is, as has been suggested, a frequency synthesizer. There are
countless circuits available, but care should be taken to use one where the
spectral purity of the output signal is adequate for use in a communications
receiver. In particular, the phase noise has to be low. One approach would to
be look for a kit with a good spec (and obviously something as simple as
possible). A Google on "frequency+synthesizer+kit" and similar brings up lots
of information.

A hundred dollars can be quite a bit, likely the rest of the parts aren't
that much (unless someone is buying all new parts).

The thing about a synthesizer is that the original poster only needs
well spaced frequencies, so the reference frequency can be 500KHz, which
allows for much easier filtering than narrower channels (or, the early
synthesizers in the seventies that replaced 8MHz crystals in 2M FM rigs,
not only did they have to deal with close together channel spacing
of 10 or 15KHz, but since the synthesizer output would be multiplied
up by the transmitter, the reference frequency was the channel spacing
divided by how much the transmitter multiplied, which gave a terribly
low reference frequency.

Plus, these are for changing bands, not tuning a given band. A second
or so of lockup time isn't a problem since changing bands won't happen
often. So the filtering can be better without impacting on tuning. A
main tuning synthesizer with 1KHz steps starts out more complicated
because it's 1KHz steps, but then it has to change frequency rapidly,
which makes it even more trouble to design well.

Michael VE2BVW