CW Transmit Frequency VS Sidetone setting #ubitx #radiuno #ubitxcw #firmware

Tom, wb6b


I was recently puzzled about why my transmit frequency seemed to be about 1khz low on 80M. I was doing what seemed natural, using the CW key to key up the transmitter into a dummy load and check the signal on another receiver. The frequency of the uBITX when in the receive mode was accurate. 

I noticed this on the original factory firmware, but switched to the CEC because of the additional features it provides, and so I could experiment with more parameters to adjust vs the transmit frequency shift. What I discovered is, as with the factory firmware, the transmit frequency is shifted. With the CEC firmware I was able to determine the transmit frequency shifts by the amount of the sidetone setting. Varying the sidetone setting lowered or raised (depending on the LSB, USB, CWU, CWL setting) the transmit frequency by the same amount. This is only when keying the transmitter with the CW key. PTT for SSB does not seem to be shifted.

Call me old fashioned, but shouldn't the radio transmit on the displayed frequency and any frequency offset to create the tone for CW be done as a receive frequency shift, such as RIT? Maybe the preference has changed.

The CEC firmware has defined settings for the SSB and CW modes, so setting a receive offset in the CW modes would seem like the solution. On the original factory software the solution is not as clear.

Tom, wb6b

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