PIXIE 2 CW TRANSCEIVER

 

The Pixie 2 is a small minimalist CW transceiver, based upon ideas from Oleg Borodins Micro 80 TRX. The circuit requires very few parts to make a fully working QRP rig. It is a two transistor transmitter, using 2N3904 transistors. It has a crystal controlled Colpitts oscillator which is left running and a keyed PA. No external mixer is used to feed the audio amplifier. The mixing is done at the final amplifier itself, and the resulting audio taken off the emitter, this forms a simple DC receiver.

The audio output is provided from an LM386 integrated circuit, and will drive a small speaker or headphones. 

CLICK HERE TO SEE THE CIRCUIT DIAGRAM

The original circuit has full CW break in operation. When the key is pressed down it transmits and receives when the key is up. There is also no tuning on the original circuit, so if you want to operate on a specific frequency such as the QRP frequency(3.560MHz) all you need to do is insert the correct crystal. Since the original circuit there has seen many modifications to improve the performance. It has no RIT (receiver incremental tuning) and one such modification is to insert a SPDT switch and two capacitors in series to provide a transmit/receive offset frequency.

The pixie 2 is available to buy as a kit from several companies with a small printed circuit board, thousands have been successfully built and used. I personally find it much more interesting ( and cheaper ) to totally homebrew the set myself from the components I can find in my junk box, or buy the components individually. 

I built my transceiver into a standard tobacco tin as I have several of them. I decided to build it ugly style, using copper clad board off cuts as stand offs, and soldered any components which needed grounding directly to the main pcb board. (see photo below).

I also build my set with a switch and a 1nf and 39pf capacitor in parallel to provide an offset of around 600hz, this is very useful if a station is transmitting slightly off frequency.

This a very good beginners project if you have never built a transceiver before. It is designed to work on other HF bands from 160 to 20 meters and all that is required for another band is to change the value of L3 and a crystal. The power output is only 200 to 300 milliwattts from a 9 to 12v supply. Although I have heard of people getting over half a watt by using different transistors. Since the oscillator is always running there is no problem with key clicks and it transmits a clean and stable signal. However there is no sidetone, but it mutes the receiver and produces a noise through the headphones in time with the keying.

I have tested the set with a local amateur station first to check the output is clean, and the RX is working before trying to make other contacts. You will have to be patent when trying to establish any QSOs, it can be very frustrating with such low power. But when the propagation is right there have been reports from stations using the pixie making contacts hundreds of miles away. You will need a good outdoor antenna such as a dipole or end fed wire through an ATU.

Once you have completed the set and checked all the wiring, all you have to do is plug in the power lead, Morse key, earphones and antenna and you will have a fully working rig. If you find the output power much lower than 100 milliwattts then:

 Check that the first transistor nearer the crystal is biased correctly.

 Check the 47k and 1.5k resistor values are correct.

 Swap T1 with a different 2N3904 or try a one with a better gain (2N2222).

 Try using a different type crystal.

I hope you build and enjoy the transceiver, and make some good QSOs.


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