[amsat-bb] Looking for 8.8125 MHz xtal
ko6th.greg at gmail.com
Thu Jun 1 17:31:39 UTC 2017
Whoa, your message raised a bunch of mental dust... Is this for the
infamous Drake 2880 downconverter?
Perhaps as an alternative, the approach I took with mine was to not
force the IF to be in the 2m ham band, but rather to center it in the
Drake's original 200-400mhz passband. I would then use my ICOM IC-R7000
all mode scanning receiver for the remainder of the RF chain. A local
oscillator frequency of 2100mhz put AO-40's 2401 mhz downlink at 301 mhz
(easy math). It ended up working reasonably well.
Putting the IF outside the ham band gave me the flexibility to use
either (any) ham band for the uplink, without worrying about
interference. If you are looking to a future as-yet unknown bird, that
might be a good idea. If they use 2m for the uplink, using that for the
IF as well is going to be a problem. It also left (and used) the
Drake's original passband filtering unmodified, improving the unit's
performance. In place of the ICOM receiver, I would now use an SDR
Dongle, something not yet available back in the day.
The crystal I ordered was 8.203125 mhz. It was from ICM, but perhaps
they might have that value (or something close to it)? Their part
number was EX45AF15.
Zach Metzinger wrote:
> Hello all,
> I'm slowly working through my backlog of projects, and I found the MMDS
> LNB that I'd planned to use for AO-40. I'm hopeful that we'll
> eventually have another 13cm transponder and I'd like to find the
> requisite 8.8125 MHz crystal for the LO conversion.
> ICM did respond to my inquiry, so they're not totally out of business
> yet, but they don't have it anymore.
> Does anyone have a spare crystal they'd care to part with for a
> nominal price?
> Specs from one of the webpages:
>> Crystal Update Information
>> The original crystal has been analyzed by International Crystal. A
> +replacement crystal should have the following characteristics:
>> The crystal is in a HC-49U holder
>> 33 pF load capacitance
>> Accuracy of 10ppm at room temp and 10ppm -30 to 60 celsius.
>> Frequency = 8.8125 MHz for a 145 MHz IF output
>> The specification number at Internaltional Crystal Mfg. is
>> EX49AF320119. Their catalog number is #525345, 8.8125 MHz
> --- Zach
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