Had a great experience helping my grandson build this kit. It works, but the regeneration is somewhat unstable, more so than I am used to experiencing. (I have built and experimented with several regenerative radios, got them working satisfactorily, so I am familiar with their usual behaviors.) Here's what I tried to improve its performance and the results I obtained.
1. Replaced the antenna gimmick capacitor with an adjustable trimmer capacitor. This helped somewhat and was a notable improvement.
2. Increased battery voltage from 9 to 15 volts. Same as 1., above. Much louder audio in the speaker.
3. Tried reducing the regenerative feedback coupling loop through the center of the torroid coil, by moving the one turn wire as far from the coil as I could. Again, same as 1., above.
4. Substituted a 2N2222 for Q1. No change, one way or the other.
These changes all helped, but not as well as I had hoped. The set receives cw and ssb very well on 80 meters, but is very unstable on the entire higher band.
Turning to the Internet for answers, others have noted that in regen receivers with bipolar transistor types, such as this one, instability issues are noted because the transistor detector has too much gain. Others noted that FET type transistors are much, much more stable as a detector, with the regeneration functioning much smoother and predictable.
So, at least the Ozark Patrol makes a fine receiver for QRP cw, but only on 80 meters, and not 40 meters,at all.
Has anyone remedied similar problems? Would an FET rather than a bipolar transistor work better as a detector in this receiver? Any suggestions would be appreciated.
... Jerry Wysocki, KC9JXE