[amsat-bb] Looking for 8.8125 MHz xtal

Greg D ko6th.greg at gmail.com
Thu Jun 1 20:29:10 UTC 2017

Hi Zach,

Oh, ok.  No direct experience here for the CA LNB, but I seem to
remember people modifying it in similar ways to the Drake.  If so, the
same technique could work.  The idea is to give yourself the maximum
flexibility for whatever bands and modes might be used in the future.

Don't forget, an SDR dongle can work very well mobile, as laptops do
well in that environment, and could set you up for some of the digital
modes that could be employed.  I even plugged mine into my Android
tablet with SDRTouch.  Lots of options for these versatile gems.  Many
use them for the current crop of satellites, but be sure to get one with
good front-end filtering (or add it externally) or you could get a
strong desense.

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.

Good luck,

Greg  KO6TH

Zach Metzinger wrote:
> Hello Greg,
> Good guess, but not quite! This is a California Amplifier LNB that I picked
> up when AO-40 started having problems, so I tossed it in a box and forgot
> about it. Recent work has me digging back into those boxes and going down
> rabbit holes long since forgotten about. :-)
> Using an SDR or a general-coverage receiver is a good idea for fixed-base
> work, but I don't have anything mobile that is general coverage. I do
> appreciate the ideas!
> --- Zach
> N0ZGO 

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