Well, I have..? sort of.? I think you are missing some important steps though.
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Signals available in an R-4 are the PTO (5-5.5MHz on all bands) or the INJ (11.1MHz above operating frequency).
The 2NT needs an on operating frequency (or sub-harmonic?) signal.
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And don't forget you need a frequency offset of your desired cw audio tone.
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I built a "transceive adapter" with an Arduino and Si5351 board.
I measure the PTO frequency, do a calculation, then program the Si5351.
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I used it to transceive my 75S-3B with my T-4XB.? Worked slick.? I also modified my B-Line with Arduinos and Si5351s in both
R-4B and T-4XB and transceive by one-wire digital bus.
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Can't just use a "T " connection but it is possible with some hardware and software creativity.
73,
Gary
WB6OGD
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Gary WB6OGD