Pititico CW Transceiver

Pititico CW QRPP transceiver designed by PY2OHH. One of the smallest and simplest transceivers designed around a 2N2222 transistor.
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Pititico CW transceiver has a consumption in RX of 1.5mA and a power of about 500mW. With a few modifications and using other transistors, the power can get as high as 1W. I actually built an older version, having the output power over 1W with a 2N2222 transistor. Unfortunately the transistor was heating up too much so I ended up lowering the power down to 500mW.

THE SCHEMATIC

I found the original schematic designed by PY2OHH long time ago and I always wanted to build it. I built a few versions using various schematics I found online. One of the versions is in the video presented on the bottom of the article. The one described in the article is closer to the original schematic, with little improvements. In the video I also had some LED’s and a buzzer that I removed later on. I wanted to reduce the power consumption.

A big Thank you to Miguel ( PY2OHH ) for helping me understand the circuit and fix some of the issues. One day I hope to have you in my Logbook Miguel. Thanks for all the help.

PITITICO CW TRANSCEIVER SCHEMATIC

SCHEMATIC DESCRIPTION

On RX the circuit works as a direct conversion receiver, where the 2N2222 acts as oscillator. The 10K resistor limits the circuit current to 1.5mA. The capacitor C3 should be between 68pF up to 82pF and this value will set your offset frequency on RX. The value of 82pF generates an offset close to 800Hz, the one of 68 pF has an offset of approximately 1kHz. I opted for 68pF and I am also adjusting the frequency offset with the help of the trimmer capacitor CT. You can watch more on why I am using the trimmer capacitor in video presented in the Pititico II article.

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.

The capacitor C4 should be between 120 to 150pF. I changed the value to 470pF increasing the power of the transceiver to 700mW. I also placed a modified Pi Network filter on the output that acts like a bandpass filter. This helped me get rid of the AM broadcast band interferences.

PITITICO CW TRANSCEIVER PCB BOARD

I decided to build my Pititico CW Transceiver in a small wooden box. I also made a PCB design that you can use to make PCB boards using the toner transfer method.  Unless you want to order the PCB boards from PCBWay as I do.

BUILDING THE PITITICO CW TRANSCEIVER

To listen to the audio output, you should use either a 300 Ohm phone speaker ( didn’t work for me ), or even better an external powered speaker. I’m using an LM386 amplifier set to the higher gain possible. If you do not wan to use an external amplifier, I would recommend you to try building Pititico II, that has the audio amplifier included in the circuit.

As you can tell, this is not exactly my prettiest built, but it works perfectly. I wanted to test it before designing the PCB board. I really loved the wooden enclosure I had and I wanted to keep it like this. In the video down below is an older version. It worked fine but I still had AM broadcast band interferences. On the new version I built, I also moved the crystal on the top panel so I can change the crystal for other ( 40m band ) frequencies.

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.

Play Video about Pititico CW Transceiver Designed By PY2OHH

In my case the filter helped me get rid of most AM broadcast band interferences that I used to have in the older version I built in this video. I may still hear interferences now and then, but really low in the background and you can barely notice them. I actually modified the Pixie transceiver also, using a similar filter with the same good results.

David ( DL1DN ) from QRP Lifestyle built a modified version for the 10m band, so feel free to do modifications for other bands as well. I hope you like this project as much as I do. Now all I have to do is to learn the Morse code and get on air using CW on this tiny QRP transceiver that I absolutely love.

73 DE YO6DXE

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    • Hi Lee, unless you want to build Pititico II that has the audio amplifier included into the circuit, I updated the article and now you can order the PCB board for the simple Pititico. I need to order a few as well ( ha ).
      73, YO6DXE