[time-nuts] Old xtal filter

[Bob Camp]

Hi

It would be a very unusual synthesizer back in 1955. Some sort of carrier recovery / IF
application seems more likely. 

Bob

> On Mar 7, 2016, at 6:30 AM, Tim Shoppa <tshoppa at gmail.com> wrote:
> 
> 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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