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Keying the AIDC-3733 VCO



One more thing, John:  If you are still thinking about how to key the
AIDC-3733 local oscillator for beacon purposes, you might consider
switching the DC feed to that "415" MMIC buffer amplifier.  I can't see
an easy way to switch anything else in the PLL or VCO without creating a
chirpy output.

Keying the MMIC won't be perfect.  I doubt that it would completely turn
off the signal, but at least it will be identifiable.

regards,

Mahlon - K4OQ

Mahlon Haunschild wrote:
> 
> John,
> 
> I don't think the VCO is in the 8-lead DIP; I suspect that the VCO is
> the pile of SMDs and striplines in the middle of the board.  The mixer's
> pattern is fairly obvious at the opposite end of the board, though (it
> looks something like an active rat-race mixer).
> 
> OK, taking this as a working hypothesis, and looking at the PLL/mixer
> board, let's see now... OK, the 8-lead DIP is probably the divider.  The
> "R24" SMD is probably the VCO oscillator transistor (I noticed that the
> same device is used in the IF amplifier), and the "1Pz" SMD device is
> probably the oscillator's varactor diode.  The "415" SMD device is
> probably a buffer amplifier (probably some sort of MMIC, judging from
> the extreme lack of other components around it).
>
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