[amsat-bb] test equipment for an amsat ground station

Samudra Haque samudra.haque at gmail.com
Sat Sep 13 14:57:08 UTC 2014

Cross posted to Tacos / Amrad and also Amsat-BB as it may interest

I made a ugly bug (well, The PCB was very nice when I started, and really
convoluted when I finished .. ) frequency marker box (from junk parts). I
will donate this to K3GWU amateur radio club and research station for
general use.

I used (what I had) 3.68 MHz, 40 MHz, 50 MHz, 60MHz sealed crystal

I used a voltage regulator and bypass caps to feed power into the units via
individual switches, so I can turn on any combination manually of the
oscillators, or all or some at the same time. I then combined the inputs
into a common point and from that point used a 10 pF capacitor to get an
output to an SMA bulkhead connector through a brass box.

Of course, I then needed a 3.3V regulated output for a microprocessor so I
put in an additional 3.3V LDO as well inside the bus and all components are
happy now. I even put an LED just to satisfy my curiosity and then sealed
all in a box.

I do see on a simple analog scope all wave forms and my frequency counter
shows the fundamental frequencies produced. A spectrum analyzer (thank you
K0BRA) shows different products of the frequencies.Obviously the
frequencies I saw were just whatever the crystal oscillators I had on hand,
so they can be replaced, or added to.

In this line, what improvements could I do to make it an useful general
purpose box for testing in the radio shack, and for AMSAT birds, is there
anything of interest that might be useful to qualify a station ? One could
use a microprocessor to switch in circuits, that much I can do, but which
type can be used to generate accurate frequency standards ? If only a clock
pulse generator (square wave) source was available, what type of circuit
would allow multiple frequencies be slaved to a crystal standard ? Any old
schematics reference would be appreciated.

I even saw how easy it is to use a audio transformer to modulate the power
leads and transmit QRP AM on the 0.5m length RF cable. I can now use this
to verify operation of the RF splitters and combiners.

73 de N3RDX @ K3GWU

if you are in Foggy Bottom area of DC and have an interest in ham radio,
I'm at GWU.

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