[time-nuts] Old xtal filter

Tim Shoppa tshoppa at gmail.com
Mon Mar 7 06:30:26 EST 2016


For crystal lattice and especially ladder filters, a Q of 10,000 is very
much in the "sweet spot" if you are starting off with bare crystals in the
Q=50,000 range. Smaller 30-100kHz tuning fork crystals often have Q's
around 30,000-50,000 but I don't know the details for the larger tuning
fork cuts.

I like the "Serial No 2".

I betcha they knew they wanted a 10Hz bandwidth filter and chose 100kHz for
the center frequency.

100kHz is occasionally the last IF of receivers that mostly use LC
filtering at that stage. It is not unprecedented to also allow a crystal
filter there although usually there would be a "phasing control" that lets
the shape/center of the crystal filter be tweakable.

10Hz seems too narrow for CW work. But nice round powers of 10 are common
in synthesizers. Wonder if this was a cleanup filter in the innards of a
synthesizer.

Tim N3QE

On Sun, Mar 6, 2016 at 2:31 PM, Joseph Gray <jgray at zianet.com> wrote:

> Assuming I made the pictures small enough, attached are two images of
> an very old crystal filter that a friend found. The strange thing
> about it is the bandwidth - 100 Hz. What could this have been used
> for, with such a narrow bandwidth?
>
>
> Joe Gray
> W5JG
>
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