[amsat-bb] Looking for 8.8125 MHz xtal

Zach Metzinger zmetzing at pobox.com
Thu Jun 1 21:47:03 UTC 2017

On Thu, Jun 01, 2017 at 01:29:10PM -0700, Greg D wrote:
> One of your challenges is going to be knowing exactly what the
> conversion equation is, i.e. where exactly your LO ended up.  Given the
> frequencies and multipliers involved, a very small offset in the LO
> crystal can result in a large offset in actual receive, making it
> difficult to find the satellite the first time.  I think mine was off by
> something like 50 mhz on AO-40, even after tweaking the LO with a
> frequency counter.  Very touchy.
> For testing, and given that there's not much ham-related stuff on that
> band, you might scan the horizon and count microwave ovens (2450 mhz
> -ish), though they are not very frequency-stable.  Best is around dinner
> time :)  I also had good results listening for the 17th harmonic from a
> 2m transceiver fed to a diode as the load (144*17 = 2448).  You might
> even try that with the 18th or 19th harmonic (2592 or 2736 mhz) on an
> unmodified unit, to be sure it's still working.


That's a great idea on the 2m rig as an exciter for a diode comb
generator. I'll have to try that out tonight on my unmodified unit! I 
assume that you attached the diode on the other side of a 20 dB pad 
to give some sort of reasonable return loss for the rig?

Many thanks go to Alan <wa4sca at gmail.com> for providing the requisite 
crystal. My alternate plan was to replace the LO generation in the unit
with a custom PLL board. That might be interesting to do and then compare
the xtal modification with the custom PLL for phase noise and overall 

--- Zach

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