40 Meter Transmitter
I had built the AMQRP's Tin Ear 40 meter receiver kit and enjoyed listening to it, but I thought it would be neat to build a companion transmitter for it. I had found plans for a simple transmitter on the internet called the "Michigan Mighty Mite." I used this design to build a 30 meter beacon, and the simple design appealed to me. The Tin Ear is a simple receiver, so I thought building a simple transmitter would be the way to go. It would be fun to get back to basics, plus I was intrigued by the thought of having a QSO using such low power.
The transmitter design is very simple and anyone can build one with a minimum of cost & fuss. As with the 30 meter beacon I built using this design, I had to substitute parts to use what I had on hand. Instead of a .05 uF capacitor, I used a .1 uF. I didn't have any 27 Ohm resistors on hand, but did have some 30 Ohm resistors, which is close enough in tolerance. Finally, I substituted a 4124 transistor for the 2N2222 since that's what I had, and any general-purpose NPN transistor can be used. Instead of using a variable capacitor from an old AM radio, I decided to try an air-variable capacitor I had on hand. I wanted a varicap I could easily adjust from the front panel, and the air-variable cap I used had a long shaft that I was able to attach a knob to. Adjusting the capacitor will change the frequency slightly, an advantage I wanted over a rockbound transmitter. The capacitor allows the transmitter to shift frequency upwards about 4 KHZ. The frequency range of the transmitter is about 7040-7044. Power output is about 100 mW.
I cut a small piece of PC board about an inch square and cut grooves into the board to make different connection points. I then soldered the different components to the board. I wound the tank coil around a 35mm film canister.
The above photos show the completed board. The left photo also shows the completed tank coil and air variable capacitor waiting to be installed. The photo on the right is a closeup of the completed board. Since the photo was taken I added a small metal clip to the transistor for a heat sink. It's probably not really necessary, but I thought it would be better to be safe than sorry.
The case I used is a candle tin that was given to me by a ham friend of mine. I'm not sure exactly what kind of metal it is made from but appears to be stainless steel. The candle that was in the tin was a scented candle that smelled like chocolate chip cookies. The tin still smells like that and this was the best-smelling project I've ever put together. I drilled a hole in bottom for a screw to hold the 9V battery holder in place, and everything fits in place nicely inside the tin. The 35mm film canister was just short enough to fit and was glued in with super glue.
I installed an SO-239 jack in the rear panel for the antenna connection. A 1/4" phone jack was installed in the front panel for a CW key. In the spirit of keeping it simple, I opted not to use an on/off switch as the transmitter uses no power until keydown. A power switch would have been redundant. The knob for the variable capacitor was harvested from an old CB. I also stuck on four rubber feet on bottom of the case.
Overall I think the candle tin makes a nice case for the transmitter and makes it look nice next to the Tin Ear receiver. I was very pleased with the way the transmitter turned out.
