On Fri, 26 Mar 2010, bpnjensen wrote:

On Mar 26, 7:09*am, "Brenda Ann"
wrote:
"dave" wrote in message

...

bpnjensen wrote:

It only has the stock - including the two ham bands 20m and 80m that
puzzle some folks (why not 13 and 60 for SWL?) but it has the spaces
for two additional, and I think I know some companies out there that
can make custom crystals for the radio. *I expect that I will try to
get some for 60m and for 13.5 - 14 MHz. *Since each one requires the
addition of an internal cap, these may be it for awhile - or maybe
I'll get fancy and come up with an easy system for plugging crystals
in and out with a variable cap so I can get other bands. *We'll see.
I still need to perfect my cornball antenna system.

ICM in Oklahoma still makes them.

You could always buy or build a VFO (or a stable signal generator) and mark
the frequencies you need to set it to for each band

Interesting idea?? If I did this, would it be connected directly to
the crystal socket? The radio has an internal VFO, but it comes after
each crystal.

If the oscillator in the radio is right, all you'd need is a coil and
variable capacitor. Some crystal oscillators work with an LC circuit
connected instead of a crystal, some won't work that way.

But this is really a silly idea. You'd have to build a nice stable
oscillator, one that worked up towards the near 30MHz, and with good
calibration. Unless you get fancy, you'd have to have a bandswitch
for the oscillator to cover the full 30MHz needed, which is extra
complication and a source of instability.

It would work to give you a peak at full coverage, but I sure
wouldn't suggest it as a regular thing.

That's the whole point of the receiver. It's in effect a receiver
that tunes a fixed 500KHz segment of the spectrum (I can't remember what
frequency range) with a crystal controlled converter ahead of it to
cover the different bands. The variable oscillator thus can cover
just a small segment (which gives that uniform calibration across the
bands), and at a low enough frequency to be stable. Plus, it doesn't need
to be switched to change bands. You lose the key feature if you toss out
the crystal control of the converter and use a variable oscillator there.

At this point, it shouldn't be that much trouble to build a synthesizer
that makes the first oscillator as stable as a crystal, but allows a
signal that can be tuned in 500KHz steps across the 1 to 30MHz range.
A 500KHz reference is pretty easy to filter, unlike synthesizers that
have 1KHz or lower steps. That's what everyone went to almost forty years
ago when solid state meant synthesizers were relatively easy to build and
there were still lots of receivers that didn't tune the whole shortwave
band because the cost of crystals were too high.

An alternative is to study the oscillator and decide if it will be fussy
about crystals or not. If it's not, then start looking for cheap crystals
of appropriate frequency, and then use those. The manual for the receiver
will give the formula for ordering crystals, but that would be costly.
What some noticed with that design of receiver in decades past was that
one could often get by with additional coverage by using oddball crystals.
So instead of paying to have a crystal ground for a specific frequency,
say 22MHz, you might find one that 21.454MHz and live with having to
calculate the frequency (or make a chart). The frequency will still be
as accurate as the dial, you just have to add the oddball crystal
frequency to know where it is tuning. Or if the oscillator is of
the right type, one might find an 11MHz crystal and it would not only
oscillate in the receiver's oscillator but put a good signal out at
22MHz only, so you get the frequency range you want.

Michael