Paraset Pixie

 If you know me, you'd know that I'm a huge fan of homebrewing equipment. I feel that it brings out the true side of ham radio operators. While a nice Kenwood or Yaesu 100W rig is good to have, there's just the feeling of satisfaction in building your own equipment, whether it's built from a kit or from scratch. I don't know why, but I'm obsessed with the Pixie QRP kits. Coming in at a price of near $5 all the way up to $10, it's a reasonable build for anyone who wants to understand how simple a transceiver can actually be. Plus, it can be used for on air operation!

There are many drawbacks to the Pixie, including its wideband receiver and its vulnerability to broadcast band overload. However, in these flaws there is room for improvement. One such improvement is making it frequency agile, with no more than a switch, a crystal, a ceramic resonator, and a variable capacitor. Recently, I have been working to make the Pixie kit into a full-blown mini paraset kit, like the ones used by spies and soldiers alike during the WWII days. It is small enough to fit into a recipe card box, measuring about 4" x 6". Complete with a metal faceplate, a 12VDC receptacle, a BNC antenna connector, and a 50K potentiometer for RIT, this will hopefully be well worth the time and money.

Originally, I had planned to put on a DDS VFO with an AD9850. Unfortunately, I felt that this would take up way too much space and would consume a fair amount of time. In addition to this, it would take away from the simplicity of the Pixie, and utterly ruin the effect of a field transceiver. What I opted for instead was a simpler solution, courtesy of Peter Parker, VK3YE. Below is one of the many videos that I've used along the way.

Once you have this mod completed, the operating trick is easy: find a frequency that is open, with little to no noise activity, and call CQ. One thing that VK3YE explains in another one of his videos is the problem with many QRP rigs. These rigs are frequency-locked, meaning that they are agile for only a few hundred hertz; whereas with this mod, the Pixie becomes operational from 2 - 3 KHz (crystal) all the way up to 100 KHz (resonator), a much-needed modification if you're going to use it on the air. On 40 meters, this is essential and helpful. Here is a rough prototype diagram of what the paraset will hopefully look like:

As you can see, the KEY socket can also be used to transmit Feld Hell. In my previous post, I mentioned a circuit that you can use on any CW transceiver to transmit Feld Hell via an optocoupler. It converts the AFSK signals from software like fldigi into OOK, which is what the Pixie uses to transmit Morse Code. One thing that I must point out is:

CW is a MODE, NOT just Morse Code

Feld Hell is a CW mode, as is Morse Code. I haven't found any other modes that fall into CW other than Feld Hell and Morse.

Now that that's clarified, let's get back on track. Below is an image of my partially-completed paraset.

As you can see, I have a "dummy Pixie." This Pixie doesn't work(?) as I accidentally soldered in the amplifier transistor backwards and, in the process of removing it, mutilated the PCB. The 12VDC socket and the 50K pot have both been installed on the faceplate. As I write this, the rest of the parts are on the way from Amazon, so hopefully I'll get a completed photo up here at the end of the week.

In my opinion, this is a worthwhile modification. Buy yourself a Pixie kit off of eBay or Amazon, get the SPDT switch and the variable capacitor, buy a crystal or two, and a ceramic resonator. The final cost of this project is well within the $20 - $30 range, a cost that is relatively within the budget of a ham who is on a budget, or who wants to get on HF fast.

I can't guarantee that you will be heard the first time, but that depends on your location, your antenna, and the power output. 9VDC will yield a lower power output (around 300 mW) than 12VDC (a bit under 1W). A 40m half-wave dipole performs great with this little radio.

One other thing I should mention: This radio doesn't only work on 40m. You can modify it to cover 160m - 6m with a change of LPF values. That information is below:

Notes: For 10 and 6 meters, replace the oscillator capacitors (C3, C4, and C7) with 47 pF capacitors. For 80 meters, add a 100 pF to C7 to jumpstart oscillation. You might also try experimenting with different transistors to see which one provides the most power output. A 2N2222 or a 2N5401 may give better results.

I know that this is still a work in progress, but I hope that by the end of the week or the beginning of next week, I can update this post with the completed project.

Stay tuned for an update soon to come!

UPDATE (1-24-22): I completed the Pixie kit, but to my dismay there are a lot of areas to troubleshoot. I went ahead and replaced the transistors with 2N2222s, which seems to work fine. The variable capacitor that I've used absolutely cannot touch anything metal, including the faceplate. Doing so will result in an awful sound coming from the audio output as well as the sidetone buzzer. 

Next, the RIT is not working as I had previously hoped. It won't even function at all! I'm not sure if there is something in the circuit or if it is the potentiometer itself. And that brings me to my next issue, which is the frequency settings. As of now, Digi-Key has 7.2 MHz resonators out of stock until April, so I went ahead and soldered in the 7.023 MHz crystal. You can still use the same layout as VK3YE mentioned above.

So was this project a total failure? Absolutely not! In fact, the receiver works quite well and I'm pretty sure it transmits fairly well. Although there are a few kinks here and there, I'm pretty sure they will tackle themselves. With a bit of diagnostic testing, this kit will be ready to take out into the field in no time! If only I could find the time though...