My Second Modification

The kit is fairly easy to solder together and it worked right away when I first powered it up. For an antenna, I just connected a long random wire that I routed out of my window and into the backyard.
However, a major issue was that the audio signal consisted mainly of local broadcast radio stations that covered all the CW signals that I was after. I figured that the broadcast radio stations were entering the transmitter through my random wire antenna. The output filter of the Pixie to which the antenna is connected, is just a low-pass filter that allows all lower frequencies, including AM radio stations to pass into the Pixie. Thus, I decided to replace the output filter with a band-pass filter for the 40M band. I came up with the following design:


A band-pass filter for the 40M Pixie Transceiver

It is fairly easy to switch the standard low-pass filter with this filter by replacing the two capacitors and the inductor of the original circuit with the LC combinations shown in the circuit above. Here is how this looks on my circuit board:



I replaced the original low-pass filter with a band-pass filter.

After this modification, all the broadcast radio stations were gone and I could clearly hear the CW stations. On transmit, I still get the full output power of about 1 Watt when operated with a 13.8V power supply (measured using the MFJ-813 QRP SWR Wattmeter). Now I had a working 40M CW transceiver and could start learning Morse code ...