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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 28th May 2020, 8:36 pm   #21
SiriusHardware
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Default Re: Kenwood TM322. (Actually a TM-733).

Page 6 of this Kenwood manual - not the same radio, but the same KRR-C001 part and a good description of it.

http://www.catlog.net/_Descarregas/M...d%20TM-231.pdf

Presumably the discrete external pull up resistors and the complex ladder network inside the package combine to produce the desired voltage output for each possible binary input value.

Maybe the choice of value for the external resistors determines the size of the output voltage swing?

Last edited by SiriusHardware; 28th May 2020 at 8:43 pm.
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Old 28th May 2020, 10:32 pm   #22
Jon_G4MDC
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Default Re: Kenwood TM322. (Actually a TM-733).

Thanks for swelling my Kenwood "gen" folder even more!
Never lose a .pdf...hehehe.

I'm no expert on this but I suppose you could mux the output lines in a way which generates the wanted tone frequency as a piece-wise sine wave with a few bits up to the maximum of 7bits resolution?

In that way there could be some level control from the uP, but then lower output levels would have more THD? Y/N?
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Old 28th May 2020, 11:12 pm   #23
SiriusHardware
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Default Re: Kenwood TM322. (Actually a TM-733).

The waveform resulting from less bits being used would be rougher/ lower resolution, but you are right, instead of utilising the full output swing of the DAC you could output a reduced range of values and thereby control the size of the output waveform to some extent. Imagine if it got to the point where you were only using one bit. The output wouldn't be much of a sine wave.

The 'official' way to change the size of the output swing without degrading the resolution of the signal would be to change the value of those fixed resistors and continue to output a 7-bit sinewave to the resistor ladder.

If the aim was to reduce the level of CTCSS tone going out to both RF PCBs, probably the simplest practical method would be to insert a fixed or variable divider after the three-component filter.
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