Michael,
Not sure where I saw it, either here or on emrfd
email group: the quality of the capacitors
used in a crystal filter are quite important. Using NPO or C0G
is highly recommended.
Other ceramics have a piezo-electric feature that
is not desirable.
Also, grounding the crystal cases is of paramount
importance.
Rod KM6SN
On 04/13/2018 08:22 AM, Michael LeBlanc
wrote:
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Friends:
I'm scratch-building a uBITX, and completely new to building
crystal filters. Attached is the response curve of the 12MHz SSB
filter using my PHSNA.?
Does this look like it will work satisfactorily in the
radio? To select the crystals, I used the K8IQY crystal test
fixture and chose the closest ones to 12MHz from a bag of 50
inexpensive computer crystals.
I don't know if my PHSNA is accurately calibrated, so although it
looks like the filter passes between 11997 and 12000, I'm not sure
how much error there is in the frequency readings. But I'm pretty
sure that the -20dBm passband is less than 2.5khz. If the passband
is slightly to one side of 12MHz, does that matter?
I've received a new bag of 100 crystals, and I'm wondering if I
should take the time to characterize all of them and replace the 8
that are currently on the board with ones that have a closer
match. Any thoughts?
-Michael VE1LEB
