The Ten Minutes Transmitter it is so far the easiest to build CW transmitter I found. With a handful of parts you can get on air in no more than 15 minutes.
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I wanted to start experimenting with simple CW transmitters. Searching for the Michigan Mighty Mite on the SolderSmoke blog, I discovered the Ten Minutes Transmitter, Walter’s Sunrise Net Special version of this simple CW transmitter that caught my eye right away. The Ten Minutes Transmitter built in the video above, was actually the first CW transmitter I ever built. The version down bellow is what I currently have.
I decided to start with this one since it was an easy build and had a low parts count. I think it only took me about 15 minutes to build this little transmitter, that including making the PCB board. It worked right away with not many adjustments needed. It sounds great and the power output is around 500mW.
The Ten Minutes Transmitter was originally published by G4RAW in SPRAT 82 / 1996. Keep in mind that built after the original schematic, you will need a low pass filter to use it on air. This transmitter loves offering you some really nice harmonics. I opted for a simple Pi network low pass filter.
This is a slightly modified schematic from the original. I placed a simple DC voltage filtering on the input, together with a diode acting as reverse voltage protection. There is also an ON / OFF power switch and an LED power ON indicator. On the antenna side I also placed a simple Pi network low pass filter. Is not perfect, but it does an acceptable job. I made my versions using either a 2N2222 transistor, 2N2219, or BC107. I prefer the metal case versions, because I can place a small heatsink on top. Do not use a regular plastic case 2N2222 or 2N3904 transistor as they will burn quickly because they overheat.
TUNING THE TRANSMITTER
This transmitter seems to cover the entire HF band. So pick the crystal for the desired band ( 7.030 MHz in my case ) and with the help of C4 – 1000pF variable capacitor, tune the transmitter for the best power output and tone. In my case, a capacity value around 240pF was enough for the maximum power output. If you don’t have a 1000pF variable capacitor, you can try a 512pF capacitor or even smaller. See what works for you.
If you close the key, the transmitter will generate a continuous AM signal. With the help of a radio, tuned to the frequency in AM mode, you will hear silence instead of the usual radio static. If you tune to the signal using LSB, USB, or CW modes you will hear the CW tone.
Once you tuned the transmitter, you also have to check the low pass filter on the output of the antenna. Spread or tighten the turns on the toroid until you maximize the power output. If you are not using a crystal for the 40m band, try an online calculator to change the values of C5, L1 and C6 for the desired band. If you measure the output and you are not happy with the harmonics suppression, feel free to skip soldering C5, L1 and C6. Instead solder a jumper to replace L1 and use an external and better designed low pass filter.
Have fun with this little CW transmitter, but always remember that you should not transmit in an antenna with ought an amateur radio license. If you don’t have a license and still want to play with it, please use a dummy load instead. Do not use the transmitter if is not connected to an antenna or a dummy load as the transistors will end up in smoke very quick. I hope you enjoy this project as much as I did.
73 DE YO6DXE