[Milsurplus] My Little Converter Gets Weird...

[Bob Camp]

Hi

My bet is that it's a 5th overtone crystal. That would give you 297 Kc  
out. Since the ratio of fundamental to 5th is never exact, the crystal  
may well be correct on the fundamental to give you 339.

Bob


On Feb 2, 2008, at 12:33 PM, David Stinson wrote:

> I built another of my little converters to go in a second LF receiver
> (corrected diagram):
> http://home.netcom.com/~arc5/converter.JPG
>
> I grabbed what I thought was another color burst xtal from the parts
> bins at the goodies store.
> I also deleted the 20-100 pFd trimmer and used a fixed 47 pFd cap,  
> tuning the input with the slug in the coil.
>
> It tuned up and worked fine, but 3880 KC was showing up at 339 KC,  
> not 302.
> There was also a large SWBC image just down from the "AM Ghetto."  I  
> looked at the xtal and it's actually marked 17915 KC!  Try as I  
> might, I can't seem to find any formula that gets 339 KC out
> with 17915 LO and 3880 input.
> For some reason, this one is more sensitive than the one
> that used the color burst xtal, and a simple wave trap got rid of  
> the image.  Anyone have a clue??
>
> Also:  This set's T/R switches by killing the receiver B+,
> and I didn't want to drill any holes to bring a PTT line or put in a  
> clunky relay, etc.  So I built a voltage divider that
> cuts the 250 VDC*  down to about 5.5 volts.  I put 50-Kohms 2 watts  
> in series with 2200 ohms 1 watt
> and put a 6-volt, 1 watt zener across the 2200 ohm resistor to  
> protect the converter, should a surge or resistor change bring
> the voltage too high.  +5 to +6 volts available at the junction
> and it works great.
>
> 73 Dave S.
>
> *  Haven't tried low-B+ on this one yet.
>   Will get to it some day......
>
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