Ten Minute Transmitter, The Simplest CW Transmitter

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I wanted to built my first CW transmitter, so I started searching on the SolderSmoke blog and discovered the ten minute transmitter. 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 almost no adjustments needed. It sounds great and has a power output around 500mW depending on the transistor used and the frequency of the crystal. On the 30m and the 40m band I have around 700mW.

The ten minute transmitter was originally published by G4RAW in SPRAT 82 / 1996. Keep in mind that you will need a low pass filter to use it on air. The very first version I built was only for the 40m band, so I also included a low pass filter into the circuit. Here you have a new PCB design following the original schematic. I kept it this way as you can use crystals for other bands too.

THE SCHEMATIC

The first version I built was on a homebrew PCB board. Here in the blog article ( Fig. 1 ) I am presenting a version I tested made on a prototyping board. It was easier to swap components. I tested the 2N2222 and the 2N2219 transistors. I prefer metal case transistors because I can place a heatsink on top. Do not use a regular plastic case 2N2222 or 2N3904 transistors as they will burn quickly because they overheat quite a bit. So a heatsink it’s a must in this CW transmitter.

Fig. 1 – Ten Minute Transmitter Schematic

PCB BOARD

Here you have a simple PCB design I made and you will find in the download folder. It’s really simple to make using the toner transfer method, or simply order one from PCBWay. It could be a lot smaller but I wanted to give the transistor enough space so that you can place a heatsink on top. This way it will not overheat as much. Feel free to experiment with other transistors as well.

Optionally you can experiment with the value of the inductor if you want better results. I like to keep it as it was in the original design, but if you want you can build it for a specific band. For the 40m band as an example, the variable capacitor can be around 180pF . The cheap ones found in portable receivers would be perfect for this project.

Fig. 2 – Ten Minute Transmitter PCB Board

TUNING THE TRANSMITTER

This transmitter ( Fig. 3 ) was advertised to cover all HF amateur radio bands, so pick the crystal for the desired band. With the help of the 1000pF variable capacitor, tune the transmitter for the best power output and tone. I had crystals and tested the transmitter on the 80m and the 40m bands successfully. The 30m band also was not bad at all. On the 20m band it seemed to me that it doesn’t perform so well ( at least in my case ).

Fig. 3 – Ten Minute Transmitter ( prototype )

I also tested the 160m band with the same poor results. All tests were made using the 50 Ohm wattmeter / dummy load I built. Also I did not had a 1000pF variable capacitor so I only used 500pF. 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 place a low pass filter on the output. Do not use it on air with ought a low pass filter as it generates a lot of harmonics. 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 it’s not connected to an antenna or a dummy load as the transistor will end up in smoke very quick.

73, YO6DXE

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