12vman,
Thanks for the information. My measurement was at great variance from yours and I suspect that I did something wrong. I'll redo this with a 50 ohm load with the base coil antenna configuration and let you know what happens.
You have propose a very unique installation and I hope you keep us informed on what happens.
Neil
Neil:
I didn't think of high-level AM because of the audio power requirement if you're not running a "peanut whistle." I believe you are correct that this is quite doable for Part 15 AM. However, never having used this approach, I'll refrain from predicting any results.
Thanks for setting me straight on the effect of negative feedback on gain but not efficiency. Well, like I said, going from an old guy's memory...
Glenn
Glenn,
It's been a while since I have been inside a MW class C transmitter with more than peanut power. I run a Drake TR-3 vacuum tube unit on the ham bands (still going strong) but I believe since it is SSB that it runs AB.
You are right about the audio for higher power class C. In the '60's I designed and built a 25 watt tube transmitter for a college carrier current station. My roomate was a hi-fi nut and had designed an amplifier using a push pull pair of KT-88's. We collaborated and incorporated his design into the transmitter. It really sounded good, but the audio section was much more complex than the RF part. It operated at 800 kHz. so the matching coil on the output was rather large. We used B&W open form stock and it was about a foot long and 2 inches in diameter. It looked neat sitting on top of the chassis.
I am aware of some designs for CB and aircraft AM transmitters that apply modulation to two or three stages of the RF chain but I don't know anything about the efficiency. This approach would probably be too complicated for a part 15 unit.
When I taught electronic communications at college we had a lab where the students built a class C stage. It was modulated by supplying the tank and collector from an emitter follower to the supply and no matching network to the resistive load. The waveforms were not bad, but I regret not having them measure the efficiency so I don't know if this approach is worthwhile.
Neil