Andy Fletcher Old Homebrew Projects

Here are some notes on some home-brew projects I have done, roughly in chronological order. There is nothing new here, just projects I’ve enjoyed doing. All comments are welcome. At school I was the despair of my woodwork and metalwork teachers, and my talents in making holes in boxes have not improved over the decades. They are usually not in the place I wanted them to be. At least I seem to be able to make round holes of the correct size. Rectangular holes are another matter. I show my projects for interest rather than attempting to inspire praise.

  • Medium Wave receiver, using a 1L4 pentode valve – and a 69 V battery!
  • Audio Processor, mostly op amps.
  • C. M. Howes 20m DCRX – a direct conversion receiver kit.
  • Crystal Calibrator
  • A 2m to 10m Receive Converter
  • 40m CW Transmitter
  • RF Sampler and AM Demodulator – as described by Alan, W2AEW in his YouTube video. I recommend his videos. He has a way of explaining designs that makes them clear and easy to understand. I boxed this up using a sweetie tin (Mixed Fruit Drops for the curious).
  • AM Modulator– simply to test the AM Demodulator
  • RF Sniffer
  • Inductance tester – to measure home-brewed inductances. This is based on the tester in section 25.8.3 of the ARRL 2013 Handbook. I didn’t bother with the internal meter, using an oscilloscope instead.
  • 40m Low Pass Filter
  • CWKtiny keyer from WiMo Antennen und Elektronik GmbH. This is just boxed up with an idiot diode on the power connection and 33 ohm resistors on the key inputs. I use this with my Bencher key.
  • SDR Mixer – used with the Gqrx application to display HF signals in the frequency domain. The main part is a RealTek RTL2838-based dongle. As the dongle only handles from 24 MHz up, the HF signal is up-converted using a 100MHz oscillator and a diode ring mixer. Based on Alan’s video. Boxed up in a Glenfiddich whisky miniature tin. I’ll probably get back to this and add an LNA to the input.
  • A ramp generator to drive the sweep input of my TG120 function generator.
  • An Aerial Analyser
  • An audio Frequency Doubler
  • A Hellschreiber Modem
  • An Internet Radio based on a Raspberry Pi and the audio stages of an old DAB radio
  • An AD9851-based VFO
  • A CW Decoder based on the Goertzel algorithm running on an Arduino
  • An FT60 PTT Circuit for connecting an FT–60 VHF/UHF transceiver to a Raspberry Pi 3B+ acting as a TNC
  • Keeping a old MacBook Pro going by using OpenBSD
  • A failed attempt to make a PSK Modem on breadboard

I use the commercial test gear listed here.

The components and other hardware to make these projects were bought mostly at

  • RS Components (wide range of goods, free postage).
  • Bitsbox (friendly, quick, and efficient),
  • G-QRP Club (friendly – great for advice and hard-to-get components)
  • Maplin (expensive, but convenient as there is a shop near me)