Re: [amsat-bb] Setting the 3733 exactly on frequency

["Mark L. Hammond" <hammond@xxxxxxxxxxxxxx>]

At 05:11 PM 4/1/2001, John Harrington wrote:
>Hello to all.  I have noticed some of you have not been able to set the
>AIDC-3733 crystal frequency exactly so that 2400MHz = 144MHz.  The
>tiny trimmer does not have enough range, and some of you are setting
>the trimmer so that 2400=144.1 or 144.2MHz.   This is fine and works
>well, but there is a simple way to set it exactly.
>//
>You can zero in on very close calibration by the amount of twisting
>together of the gimmick capacitor wires.  Bend the ends of the wires
>down towards the board so the cover goes on without hitting them or
>upsetting your calibration.
>
>Best regards,  John  W5EME


Hi John,

Neat trick.  I attacked mine again tonight (fun to melt solder ;-).  I 
first put a 10 pF cap in series with the stock trimmer, by unsoldering the 
end nearest the crystal lead.  Was about the same as stock trimmer 
alone--still couldn't tune down far enough.  Next, I put a 1 pF in 
series--still not down far enough, but it was close..about 25 kHz too 
high.  So..next, I tried the 1 pF alone, without the trimmer.  Still too 
high.  So, I tried it with NO cap in place.

It was now within about 4 kHz of the desired frequency (2401 = 
144.004).  Guess that will have to do...adding any capacitance puts it 
over, so I didn't even try the wire-twist trick.

73,

Mark L. Hammond  [N8MH]

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