Pixie 2 QRP TRX

Pixie 2

I have been interested in QRP Radio since I was licenced. I have built a few projects but never a pixie 2. I have seen them in use. A friend of mine has a couple and they are very interesting. Recently I had been looking at some Pixie 2, TRX kits from China. Priced at less than £3.

Then G7AGI posted some pictures of his pixie 2 purchased from China and said it was good quality. So I purchased one. The kit is fairly easy and didn’t take long to build. A Parts list and circuit diagram is included. Along with a 5 watt 51 Ohm Resistor for testing. Mine however was a wire wound type resistor. Which is not ideal in RF circuits.

pixiebag

The above image is the way the Pixie 2 arrives. I forgot to take a picture of mine, so borrowed this image from Rich M6GPT. The components are fairly good quality and there is a few spares included. As this kit is available for 40 M, 30 M and 20 M I suspect the components for all variants are included, except the crystal.

pixie circuit

This is the circuit diagram, Its really very simple. A crystal oscillator, a small PA and audio amplifier. Which has a mute circuit to turn it off while transmitting.

pixie2I wanted to check this kit out. It looked ok but the PCB is multi-layered, so you never really know what’s going on. My initial tests showed an almost perfect sine wave at 7.023 Mhz. The Red trace above. The green trace is an FFT plot, showing the frequencies. There are no harmonics, which is good. The largest peek is the 7.023 Mhz signal. The FFT is a little noisy but I suspect this is because the sine wave is not perfect.

When I calculated the output. I found that at 5 volts I was getting 38 mW out into a dummy load. At 12 Volts I was getting 70 mW out. These figures didn’t quite seem right. The sign wave was a little unstable and at times dropped to 1.66 Volts pk-pk, at others it was hitting 15 volts pk-pk.

I inspected my soldering and component placement. Which seemed fine, so began some tests. I narrowed the problem down to the 8050 transistor. Once I removed it, I found it was faulty. I replaced it and found the pixie 2 performed much better.

During the testing, I had to hold the key closed, to get a good trace and FFT. The transistor heated up quite quickly. With proper use. The transistor can become warm. At 5 Volts the Pixie 2 is now putting out around 300 mW. At 12 Volts, It put out over 2 watts for a brief period, then fell to just under 1 Watt. My measurements are not as accurate as I would like.

During Receive. The pixie 2 draws about 10 mA at 12 Volts. During transmit the Pixie 2 draws about 140 mA. These figures are achieved with peek values on a multi-meter and so don’t represent a very accurate result. I share them for information purposes. I am currently having building work and most of my equipment is packed away in boxes. So I had to make do, with what I had out.

The pixie 2 can be run quite easily from a 12 Volt solar panel. I would suggest a fairly large capacitor in parallel to act as a buffer between TX and RX.

 

 

 

 

 

 

 

 

 

 

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