The Cranky Sysadmin A world of technology, fun, and ignorant rants.

April 21, 2013

A Break from Antenna Analyzers (Pixie II Transceiver)

Filed under: Electronics,ham radio — Cranky Sysadmin @ 8:59 pm

I took a break from antenna analyzers to find and build a rig for a friend who is in a nursing home. The requirements are:

  1. It should be very small and portable. A nursing home doesn’t have a lot of space.
  2. It should be a CW rig. My friend is proficient with CW.
  3. It should be easy to build.
  4. I need to find the components in my junk box.

When I did a google search for “Minimalist CW Transceiver” I came across the Many variations of the pixie II. I did some mixing and matching and came up with the circuit below.pixieII

This worked ok, but there were two problems. There was a lot of broadcast interference from the station about 7 miles away. There was also a lot of microphonics. Whenever I touched anything, I could hear it in the speaker or headphones. The microphonics problem was actually easy to mitigate. I dropped some hot glue on the capacitor (c12)which leads from the emitter of Q1 to the input (pin 2) of the LM386. I found the culprit by placing my finger against various components while tapping the pcb with tweezers. My finger damped the microphone effect when I touched C12. The BCI problem was also easy once I solved it, but it was difficult to find a good solution. I tried ferrite beads everywhere I could think of to no effect. I tried attaching pin 7 of the lm386 through a cap to pin 2. I tried a zener diode on the power feed of the lm386. None of that had any effect. The solution was to use a bandpass filter in place of the low pass filter (C9,10,11 and L3). Below is the schematic of the bandpass filter.80m_bpfWow, what a difference this made. There is no BCI now. If I were to add anything else to this receiver, it would be an audio CW filter. Right now, on a busy night, I can frequently hear two signals overlapping. Even with this problem, it’s a neat transceiver which can tune across the whole 80 meter CW band, and it seems to put out about 300 milliwatts. Below are a couple of pictures of the finished product before I swapped out the LPF and applied hot glue.

You can see why it's called ugly construction

You can see why it’s called ugly construction

Fits in an Altoids tin. Woohoo!

Fits in an Altoids tin. Woohoo!

Now that the transceiver is built and seems to function, I now need to produce a portable antenna… which means I should get back to my antenna analyzer.

2 Comments »

  1. Hi, would love to know if you came up with a suitable antenna for the Pixie 2. I have just finished building it and will be operating on 40m. What type of connector should I have on the plastic box I’m using for the antenna? What type of cable should I use to the roof? And finally I guess a 20m wire, split in the middle will do? What do I ground? Many thanks, Andre

    Comment by Andre — February 2, 2014 @ 12:29 am

  2. I actually built this for a ham in a nursing home, so the antenna is much more of a compromise than you probably want. I built a multi-turn small loop on a PVC cross shape with a smaller loop to feed it, and a tuning capacitor at the open end. It’s tuned for the CW portion of 80 meters. I used bnc connectors on both ends and some rg-8 cable.

    Comment by Cranky Sysadmin — February 2, 2014 @ 8:08 am

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