John's homebrew page

My interest in electronics goes a long way back - I think the Ladybird book "Magnets, Bulbs and Batteries" was one of my earliest tutors; that had me hunting for double cotton covered wire at the time when it was becoming difficult to get. I remember making a working electric motor from a cork, a darning needle, two short pins, four long needles, two drawing pins, a magnet, some DCC wire, and a battery. Very satisfying - I found my old book and here it is (the horseshoe magnet goes over the top) ...

For real electronics I was lucky enough to be given a "Phillips Electronic Engineer" kit for Christmas in 1964 (I think). This enabled me to build a real transistor radio - but also gave me the components to experiment with.

Old projects

The old projects are described on a separate page; they include all sorts of stuff, from my first (valve) oscilloscope to my first computer, programmed with a screwdriver, and a telephone modem.

Recent projects

This list is growing reasonably rapidly - here are the recent projects (most recent first):

• Transverter for 23cm
• Portable 23cm 15 element Yagi
• Low VHF wavemeter
• Comb generator
• Microwave wavemeter
• RF probe
• NiMnH battery pack
• Microwave RF sniffer
• 2m Lambda Loop loft antenna
• Anderson Powerpoles
• 2m preamplifier
• Portable 6m linear amplifier
• Portable 70cm 12 element Yagi
• Portable 2m 7 element Yagi
• Portable 2m linear amplifier
• Portable HF linear amplifier
• Dummy load

Latest project - new 23cm transverter, this time with 144MHz IF

There are several things I want to do to add to the transverter, but these would add boxes and weight which is not ideal for my /P operations for SOTA. So I want to make use of some of the things I've learned with the first transverter, and build another one which is much more compact, simpler and lighter.

This time it will have a 144MHz IF. I realised there isn't really a need to use 432MHz for 23cm, especially as I now have an old Trio 2m multimode radio for potential talkback. I'm starting with a new and much simpler local oscillator, then the transverter itself will be somewhat simpler than the first. Hopefully I can get everything, including the 5-10W PA I intend to build, into a single box. We shall see!

Here's the board for the local oscillator, 37 by 74mm in size.

It will use a computer type crystal oscillator module at 64MHz, and SMD inductors in the tuned circuits (apart from a Toko helical filter at the LO frequency).

The board was assembled a stage at a time, as usual; the power supply first, with 8V and 5V regulators, then the SMD oscillator block, then the multipliers in sequence, checked out with wavemeters, RF sniffer and RF probe at each step. I had to change the inductors for the second multiplier as I hadn't allowed enough for stray capacitance on the board. In the photo below, the SMD oscillator (64MHz) is top left; the pink trimmer capacitors are for the 192MHz circuit, and the blue for the 576MHz circuit, each with a BFR92 transistor. The third BFR92 drives the Toko 2-stage helical filter mounted on the groundplane side; the output from the filter goes into a MAR-3+ MMIC (middle right on the board).

The spare copper lands (bottom left) were for a 64MHz fundamental filter, as in the W3GHZ designs, but it works fine without; I'll try that later.

Here's the other side of the board. The 5V regulator is bottom left, the Toko helical filter top right. The filter needed about a turn or so in to get it on frequency, and adjustment is fairly flat. I checked the frequency using the 7th harmonic of the crystal oscillator (in the 70cm band), and at 1152MHz it's about 5kHz high. That's great, easy to correct for when tuning. It's about 10 times better than the spec of the oscillator!

Even without the MAR-3+ I had nearly 1dBm of output; with the MAR-3+ in circuit I get a good output at about the full 10dBm it can produce, which will be fine to drive the mixer after an attenuator. It produces a lovely absorption dip as measured on the RF sniffer connected to the coupling loop on the wavemeter as I go through 1152MHz.

Circuit to follow once I've re-drawn it - quite a few component values got changed from my original idea.

Once installed in the tinplate box I found I needed to add more supply decoupling to get rid of a 60kHz approx oscillation, but a nice 10µF capacitor soon fixed that, and it still produced the 1152MHz as required. So it looks as though the local oscillator is now done.

More soon - I now need to do the layout for the transverter proper ...