[Lowfer] LF converter, 10 meter radio, hear 600 meters

[Dick Cappels]

If the 28 MHz crystal is a third overtone type, it would probably look like
a 9.5X Mhz crystal to the oscillator. Some modifications to the oscillator
would be required to get it to oscillate at 28 MHz.  Changing the oscillator
from fundamental Colpitts to a Butler oscillator is a good way to make the
oscillator operate at the overtone frequency. Basically, you would just
change the values of  C10 and C11 on the PCB, and then add the series tuned
trap in parallel.  

You might have to add a resistor from pin 7 of the SA602 to ground to get it
to oscillate reliably.

The URL below will get you a nice article on the topic.
http://sss-mag.com/pdf/saosc.pdf

Or just Google ³Butler Oscillator².


In answer to your question as to whether you would need to add or subtract
the local oscillator to know the received frequency, the answer is: Yes,
either or both depending upon the tuning range of the receiver. The output
of the SA602 is not frequency selective, so it will generate both upper and
lower sidebands. Whether you add or subtract, depends upon which sideband
your receiver has tuned in.



On 1/2/10 6:15 AM, Andy - KU4XR at ku4xr at yahoo.com wrote:

> OK Gentlemen:
> 
> Mulling ideas over in my head, and wondering if this idea will
> perform at a satisfactorily level.  **  I have a Radio Shack
> HTX-100, 10 meter mobile, USB & CW reception. It hears fine,
> I have no interest in 10 meter mobiling anymore. So it's just
> laying in a drawer wasting away. Jackson Harbor Press offers
> an LF convertor;  http://home.att.net/~jacksonharbor/lfconv.htm
>> From what I have read about it; ANY crystal frequency will work
> with the converter. They offer 4 & 10 MHz Xtals, and an optional
> 14 MHz Xtal. QUESTION #1 ::: Would there be any reason that it
> wouldn't work with a 28 MHz Xtal ??? This could put the HTX-100
> into mobile operation for 600 meter reception with some slight
> mods to extend its upper cutoff filter frequency.
> QUESTION #2 ::: Being at 28 MHz, will the frequency readout
> require adding or subtracting to know what frequency I'm hearing ?
> The 10 MHz Xtal directly converts 393 KHz to a dial frequency of
> 10.393.00 MHz, but the 4 MHz Xtal makes you have to do some kind
> of subtraction to be on a certain frequency. That's what I want
> to know about using a 28 MHz Xtal.
> 
> Some thoughts please, I will appreciate it.  73 and HNY all :::
> 
> 
> 
> Andy - KU4XR - EM75xr - Friendsville, TN.
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