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Michigan Mighty Mite – QRP CW Transmitter
Michigan Mighty Mite is a QRPP CW transmitter that's easy to built, with a rated power from 200mW to 800mW.
Play Video about Michigan Mighty Mite QRPP CW Transmitter
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With this particular built, I only got 200mW at first, from a plastic case 2N2222 transistor. I experimented with more transistors though, getting about 700mW of output power. Also the coil I am using is different than the one presented in the videos. I will post a new video soon, and a new PCB board design to fit the new coil.
Did you know that you can also transmit AV voice signals with the Michigan Mighty Mite ? Check the video with the first experiments on the bottom of the article.
THE ORIGINAL SCHEMATIC
I discovered the schematic of the Michigan Mighty Mite on the SolderSmoke Blog, as I like to read their articles quite often. I found a lot of the projects from my “to do list” built by other people in their blog articles. And not once, the articles helped me fix some of the issues I had and made things work properly. With that in mind, here you have the original schematic of the Michigan Mighty Mite transmitter. You can build it for most of the HF bands, but I noticed it performs better on the 80m band. What I love the most, is the really nice tone it has. It sounds a lot like an old tube CW transmitters, a pleasant tone to my ears.
The original schematic is credited to two hams: Ed Knoll, W3FQJ and Tom Jurgens, KY8I.
This was only the third transmitter I built, so I did not want to make many changes. All I did in my particular version, was to place a bandpass filter on the output. I also placed a power ON LED indicator, and another LED to light up when it transmits. This one also helps me tune the transmitter. The Michigan Mighty Mite is fun to build, but it seems complicated compared to the Ten Minutes Transmitter, the very first CW transmitter I built.
MICHIGAN MIGHTY MITE SCHEMATIC
THE COIL AND SCHEMATIC DESCRIPTION
This little circuit can put out about 500mW RF on 160, 80, 40 or 30 meter amateur radio bands. The core of the design is a crystal controlled oscillator, which is fed into an RF output transformer. After you build the circuit, check if the transmitter works using a radio tuned on the frequency of the crystal. If everything went well, you should hear the tone. You will need to tune up the circuit with the variable capacitor, so if you don’t hear a tone, slowly turn your variable capacitor until you hear one. If you have an RF wattmeter, tune your circuit to the highest output power. I do that by using the 2 turns pickup coil ( L 3 ) and the LED indicator. The thickness of the wire I used was 0.6mm on a 34mm PVC pipe.
| BAND | L1 | L2 |
|---|---|---|
|
160m |
60 Turns Tapped at 20 |
8 Turns |
|
80m |
45 Turns Tapped at 15 |
6 Turns |
|
40m |
21 Turns Tapped at 7 |
4 Turns |
|
30m |
15 Turns Tapped at 6 |
4 Turns |
MICHIGAN MIGHTY MITE PCB BOARD
I will re-design the PCB board at some point, but for now this is the one I used when building the Michigan Mighty Mite transmitter presented in the video above. I designed everything in a rush, but I already have some ideas to improve it a little and make it easier to build.
BUILDING THE CW TRANSMITTER
I had no equipment to measure the low pass filter or the coil that I made for the Michigan Mighty Mite. For sure they are not perfectly adjusted. I’m also suspecting that maybe that’s why the power output it’s not as big as others managed to get. Lately I did purchased some more equipment to do measurements and adjustments. It was a lot of fun building and experimenting with this simple CW transmitter. I hope you will also enjoy it. I learned a lot about how a simple transmitter works, so it was worth building it.
EXPERIMENTING WITH AM VOICE TRANSMISSION
The transmitter can be modified really easy, to also transmit AM voice signals. I had way too much fun experimenting with this. I know for sure that my Michigan Mighty Mite version of the transmitter, will be designed to transmit both CW and AM voice. I will need a better audio amplifier, probably using transistors, for a better modulation.
73 DE YO6DXE
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Has anyone ever put this rig on 10 meters? I would like to use it for becon project I’m working on. I see from the text 30 meters and all the turns are discussed. I set-up a spreadsheet and found what seemed to be useful numbers. It appears L1 would be 12 turns and tapped at 4. I need a “sanity check” for these values. And what about the antenna link , would 4 turns be too many? I think I can work out the lowpass filter values as I have a place to go and design one.
TNX es 73 , 72
WR2C
I’m also curious. I never tried anything else besides the 40m band. Right now I am working on redesigning the PCB board so I can use a toroid coil instead of the PVC version. With a few adjustments I managed to get a little more power out of it. The problem with this one is that the transistor seems to heat up after a while in use. So I don’t know if it would be great for a beacon. Is ok for CW, but as a beacon I guess it would transmit nearly continuous. Maybe with a big chunky heatsink would work ( ha ). I will try this coming week on 10m as well with the toroid coil and I will let you know.
73, YO6DXE
I started doing these back in 2011. Even placed a 3-4 turn coil around the coil so that the RF would light up. The Watt meter showed 1/2 on some, and nearly a watt on others. Though several were at 300mW. The pics are on the Michigan Mighty Mite sites gallery. The ones with LEDs are the ones that I built.
I started placing Low Pass filters in 2017. I might have some pics of them somewhere. AE5VM
I think I know the photos if I remember well. From when I was searching about the Michigan Mighty Mite. But I will run a search again. I had issues with the power output. First when I used cheap and badly made transistors… then I also noticed that the coil is not exactly accurate. I didn’t had much time to play around lately, but I got it figured out last time I built another version with the toroid coil version.
Esse capacitor variável de 365pf é pra ajustar a frequência do oscilador?
Se bem me lembro, um capacitor variável de 1000pF foi usado no esquema original. Mas pessoalmente não precisei de um valor tão alto até agora. 365pF deve ser suficiente. Se não for suficiente, um capacitor normal pode ser adicionado em paralelo com o variável. Talvez um capacitor de 220pF sirva. É experimentado para obter os melhores resultados.
73, YO6DXE