Pititico II CW Transceiver

Pititico II CW transceiver for the 40m band. A transceivers designed around a 2N2222 transistor by PY2OHH, and improved by YO6DXE.
Play Video about Pititico II - 700mW CW Transceiver

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I always loved the Pititico CW Transceiver designed by Miguel – PY2OHH and wanted to incorporate an audio amplifier in the circuit. This way I could use regular headphones. Here it is finally, working like a charm. You want to get on air for cheap ? I think you can build this for $10, or even less than that. Is not perfect, but is a simple and easy to build CW transceiver. Initially I wanted to try the Curumim, also designed my Miguel. Since he was not so satisfied with it, I decided to use a few more parts and make a better Pititico.

THE SCHEMATIC

I found the original schematic designed by PY2OHH long time ago and I built a few versions in the past. Recently one of the YouTube subscribers ( Jesus ) asked me for help in a school project. He had to build a very simple CW transceiver for the 160m band. I thought it would be the perfect time to test this idea and see if it works. I was happy to realize that it works amazing, even on the 160m band with little changes.

There is nothing original in the circuit. All I did was to combine two circuits together. Miguel’s Pititico CW transceiver, with an LM386 audio amplifier. Of course I had to make some adjustments in order to get it to work properly, but it was worth it. It feels a lot like a Pixie transceiver, but with less parts needed to build it.

PITITICO II CW TRANSCEIVER SCHEMATIC

SCHEMATIC DESCRIPTION

On RX the circuit works as a direct conversion receiver, where the 2N3904 acts as oscillator. The 10K resistor R4, limits the circuit current to 1.5mA. The capacitor C7 should be between 68pF up to 82pF and this value will set your offset frequency. The value of 82pF generates an offset close to 800Hz, the one of 68 pF has an offset of approximately 1kHz. If you have issues with the offset frequency, you can also make some adjustments with the help of CT trimmer capacitor.

In TX the circuit works as a low power oscillator, reaching 1W and currents of 100mA. The transistor supports this current well in CW, but do not keep the CW key activated too long as the transistor will burn out.  Another problem is operating without antenna or dummy load, the transistor burns out right away.

With the 47opF of C3 and the modified Pi-Network filter ( bandpass ) the power of the transceiver is about 700mW at 12v.  The filter also helped me to get rid of the AM broadcast band interferences.

PITITICO II CW TRANSCEIVER PCB BOARD

Using the toner transfer method, you can make a PCB board in less than 20 minutes. In the video you hear me talking about the issues with the low pass filter and the AM broadcast band interferences. For that reason I already updated the schematic and the PCB board for a bandpass filter instead. So just build it as in the schematic and it should work right away with just little adjustments needed.

Or if you had enough of making homemade PCB boards, check the button down bellow. Now you can order PCB boards from PCBWay. I tried making the design in a way that is also easy to make them at home.

BUILDING THE PITITICO CW TRANSCEIVER

The Pititico II is a really simple CW transceiver. There are only a few notes and recommendations to make in order to get the best out of it. First is R2 as I was saying in the video. Try using a 0.5W, 10 Ohm resistor instead of 0.25W. Also for all the capacitors in the bandpass filter, try using some bigger ones in size, not the tiny ones I used in the video. This will help you squeeze a little more power out.

Remember the transistor is heating up quite a bit. So from time to time it will sure burn if used a lot. Fo that reason, try to install it in a socket that it would make it easy to replace. You can do the same for the crystal as I did in my first version of the Pititico CW Transceiver. For the audio output, regular headphones are the best. A small speaker may also work, but the audio signal will be weak. It was designed for headphones.

RF FILTERS AND DUMMY LOADS

Here you have a video with a short introduction to RF filters and dummy loads. Is important to learn why they are so important when building and testing any transmitters or transceivers. I hope is easy to understand by beginners.

Play Video about Pititico II TRX RF Filters And Dummy Loads

ADJUSTING THE BANDPASS FILTER

The inductor that I made for the bandpass filter was made on a T37-6 toroid. It has 16 turns of 0.4mm enameled copper wire. To adjust the filter once you finished building the transceiver, simply connect it to a power meter and spread or tighten the turns on the toroid for the highest output power.  With a 2N2222 transistor with an hfe of about 240 the output power in my case is about 700mW. You may get more or less, depending on the transistor you want to use and the amplification factor of the transistor. 

So all I can say now, is to wish you good luck building it and have fun using it. Is really tiny and easy to build and adjust, even for beginners. You can also learn a lot thanks to this simple qrp transceiver. Before I end the article, I have to say thank you to Jesus for asking me for help with his project. If he didn’t, for sure it would take me a lot longer to do this circuit. Also thank you to his teacher, Jacinto ( YV5EWX ) for giving us the hard task of finding a 160m crystal ( ha ). That was no fun at all. Building and getting it to work was a lot of fun though.

73 DE YO6DXE

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