I checked the PA of the 1209 that I built a couple years ago. It was
still working with full gain and full power output at 10 MHz (lowest I
had a decent calibrated signal generator at the time). The transmitter
selectivity is all in a triple tuned tank between the broadband buffer
and the PA stages. The coils in that circuit are standard TOKO size
coils. Ditto the selectivity in the receiver. Most of the 2m side is
untuned, just resistive matches. It should be relatively simple to make
it run on 5 MHz.
I used to have a TS-120 which covered ham bands only. When I replaced
the VFO with crystal (internal crystal) it worked (with reduced gain) at
5 MHz using the 4 MHz tuned circuits. Its possible that satisfactory 60
meter operation can be had in many vintage Omni's by adding only a
different mixer crystal in the LO string. I think the OMNI V and VI
still use much the same mixing scheme as the Corsair, just synthesize
the 5 - 5.5 MHz VFO. Might need to enable the 40m oscillator mixer with
a crystal down 2 MHz while using the 80M bandpass filters and the 40 m
PA low pass filter.
Of course, my ancient Collins S-line will tune 60 meters as it sits.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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