[amsat-bb] Creating stable LO & control head idea

["Larry P. Thomas wa0gwa" <lpthomas@xxxxxxxxx>]

At 04:37 PM 5/18/2001 -0500, you wrote:
>Paul Williamson wrote:
>
>I find that my downconverter, at least, is not stable enough for
>this to work. Its drift is often greater than the Doppler shift!

I have an idea to toss out in case is has merit and someone has time to 
work on it.  The down converter already send the IF frequency down the 
cable and the DC supply voltage up the cable.  Why not use some 10 MHz low 
pass filters (i.e. just a couple caps and couple coils) to allow the 
insertion of the required local oscillator crystal frequency into the cable 
in the shack and its extraction at the convertor end.  After extraction at 
the down converter end it could be used in place of the crystal to drive 
the PLL which creates the LO signal.  In fact, why could the crystal 
frequency not be generated by one of the low cost DDS devices 
available.  Even the cheap one attached to the parallel port of a PC should 
work.  Extrapolating on the idea a little, a PIC could control the DDS, 
thus knowing the LO frequency without measuring it, output control RS-232 
to control the serial interface on the radio serving as IF, and display the 
resultant 2.4 GHz receive frequency.  Using a rotary encoder into the PIC 
would allow the PIC to act like the receiver.  A second rotary encoder 
could serve as a RIT/Doppler/DeltaF/etc control or a second RS-232 channel 
could be feed with the tracking program.

The idea carried to its fullest could result in a nice sharp little control 
head for A040 and others.  The idea in its minimum would still result in 
stable LO frequency and should be easy to implement. I am still working at 
getting my basic receive capability up and intend to pursue this when that 
is done.  I would love to hear from anybody that thinks the idea has merit 
and is willing to work on it.

Later
Larry P. Thomas wa0gwa

- Imagine it / Achieve it - Dream it / Become it -
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