I have been in the throes of some serious building recently. The DFR (see previous post), a nearly completed WBR regen receiver, and now, suddenly, without warning, in two evenings, a Michigan Mighty Mite QRP transmitter.
Soldersmoke is one of my favorite ham radio podcasts, hosted by Bill Meara N2CBR and Pete Juliano N6qw. In the recent episodes, there has been a lot of discussion about the Michigan Mighty Mite — a QRP transmitter that is an ideal first builders’ project because of its low parts count, and the total nonchalance with which it can be built and still oscillate.
I became intrigued and did some Googling. There is a ton of material to be found, so I’m not going to link any here. There are amazing photos of these things, which apparently will operate regardless of construction technique.
Bill made the offer to supply a 3.579 MHz crystal (the color TV colorburst frequency, which happens to fall in the CW portion of the 80 meter amateur band) to anyone writing to ask for one, to be used to build an MMM. Get a lot of rigs out there on 3.579, take back the frequency… the Colorburst Liberation Army.
Well I don’t operate much on 80 meters because of the antenna I have available at my home QTH, but 40 meters is another story entirely. Although I am in the middle of the WBR regen build, I had to take some time off and build an MMM on 40 meters. It took two evenings, and oscillated on the first power up!
I used a 2N3053 transistor, and a 100pf variable capacitor, along with a crystal on 7.050. All of the parts were what I had on hand. The tank coil is wound on a pill bottle, and the odd looking heat sink is a piece cut off of a salvaged computer cpu heat sink, glued to the can of the transistor. General construction technique is Manhattan style, using MePads from QRPME.
I won’t put it on the air until I add a low pass filter, but in this video you can see it in action, being keyed with an alligator clip. The audio is from my FT-817.
You may be able to see behind the coil a bit of the a 50 ohm resistor terminating the antenna leads for testing. Based on p-p voltage measurements across the resistor I estimate I’m getting about 300mw out at 12 volts. I intend to add a back panel with jacks for a BNC antenna connection, 1/8″ stereo jack for the key and a coaxial power connector. I’ll get some pictures up when it is all packaged up.
This little project was a fun break, now back to the regen!