Dr. Barry L. Ornitz wrote:
"Michael Black" wrote in message
xample.net...

For AM, there's probably a lot more possibilities. Pull some ceramic
filters out of a CB set and cascade them, though those will be at
455KHz. All kinds of cordless phones, cb sets, some older cellphones,
49MHz superheterodyne walkie talkies and other consumer items use
double conversion, with the first IF at 10.7MHz (and a wide ceramic
filter there, the type you find in FM broadcast band receivers) and
then a conversion to 455KHz, so they'd supply the needed crystal
for the second conversion.

If you're not stuck on a specific IF frequency, there's bound to
be still lots of AM bandwidth crystal filters floating around, since
after all relatively few were interested in good filters for AM,
while SSB-width filters were very desired.

Digi-Key stocks a number of ceramic and crystal filters that might be
suitable for AM reception for less than $10 each, some for less than $2.
They are willing to sell in small quantity and are one of the better
distributors of electronic parts. Now one of the largest distributors,
they got their start selling kits of parts for an integrated circuit keyer
for hams. See:
http://www.digikey.com/.

It _might_ be possible to shift the frequency of an existing ceramic filter
up somewhat by judicious file and sandpaper work. I am not sure how much
you can cut it before you screw the geometry up too much for it to work,
though.

If you need a weird frequency like this, though, I would first call ICM
and see if they can make you something at a reasonable price. They have
standard crystals for very cheap and I bet they won't charge much for
filter crystals either.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."