Calibrating output power, TX audio input, and relationship of CW output power to SSB output power


Rob French (KC4UPR)
 

Hello!

So I'm having great fun and success with a little Teensy 3.2-based I/O module that I've added to my uBITX, including a Teensy Audio Adaptor, which is allowing me to do a bunch of different things (transmit and receive DSP, integrated USB audio input/output, various other I/O control).  Another thing I've added is a G4HUP IF buffer at the 45 MHz IF, which outputs to an RTL-SDR dongle... I've been using that as a panadaptor.  As a side benefit, although the buffer switches off in transmit, I still see the rig's TX spectrum at the 45 MHz IF when I transmit... which leads to the following.

I had to do some tweaking of the output levels out of the Teensy Audio Adaptor, as I noticed that I was easily exceeding my expected output power of 8 W on 40 meters (that's what I get in CW), and hitting 14 watts.  Looked great on the power meter, but I could see on the 45 MHz IF spectrum that I was getting all sorts of splatter.  Initially, I was thinking I would just turn down the audio level from the Teensy until I didn't see the splatter in the 45 MHz IF spectrum.  Easy enough, but I noticed that even after I cleaned up the spectrum (for example, turned down the level so that I just saw one clean spike in WSJT-X tune mode), I was still getting nearly 14 watts.

So that leads to my question, what should I expect in terms of output power relationship between CW and SSB?  I know for sure that I need to turn down the audio level to get rid of the splatter... but what if that power level is still higher than what I get in CW?  Is that ok?  (I realize the ultimate answer is looking for splatter and harmonics at the final output.)

I did implement in the Teensy software a two-tone 700/1900 Hz signal generator, so it's very easy for my to push that into my transmit audio, if that will be helpful for calibration purposes. 

Regards,
-Rob KC4UPR

One thing I added in the Teensywas a two tone test generator. 

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