BITX Update # 13

After getting the receiver front end tuned with parallel ceramic capacitors I replaced them with single  33pF ceramic capacitors. I then re tuned the filter transformers and the receiver sounded good.

Time now to turn my attention to the transmitter.

I have done no work on the linear amplifier so I wired the TX power on and listened on my FTDX100 for a signal from the BITX20. Since I had not adjusted the carrier balance trimpot or the trmmer cap I presumed I would hear something.

I didn’t hear anything from the BITX20 so I reasoned it was not running very much output. I checked with my home brew RF probe and couldn’t measure any output at all. If there is something there it is really weak.

Not seeing anything on the probe I connected the output of the main board directly to the input of my FTDX100. I didn’t have a microphone connected so the output of the BITX20 was going to be consistent and not pose any danger to my FTDX100. I also removed the microphone from the FTDX100 to prevent accidental TX from it.

With a direct connection between the two radios I could now hear the BITX20 carrier at about S9. Tuning the carrier balance pot (I used a 200 ohm trimpot rather than 100 ohm specified) and then the trimmer cap I got the carrier signal down to S6. I don’t know how strong it will be once I add the linear amplifier but S6 for a direct connection is pretty weak.

Tomorrow I might get a microphone on and see what the transmitter sounds like.


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