The Shipham Mk 2 Receiver
This project arose from a visit to The Nation Radio Centre at Bletchley Park, where staff suggested that very simple introductory projects need to be followed by something more advanced that would lead into amateur radio. The Yeovil Club kindly expressed an interest and have successfully built several of an earlier version. The receiver is initially built for the high power broadcasting stations that operate in the Medium Wave band below 1.5 MHz using Amplitude Modulation; this requires just two transistors for the RF amplifier and detector, with an integrated circuit audio power amplifier to drive a small LS or modern ear buds! With a few metres of wire aerail (ideally outside), it should be possible to comfortably receive 3 stations anywhere in the UK. The MW parts are mainly on the left hand side and include a volume control with ready wound inductors to avoid difficult hand wound high values! The instructions are very detailed for novice builders.
The next stage is to add a band switch, one more transistor and the parts on the right that turn it into a Regenerative RX for short waves – typically the 40 or 80m amateur radio bands depending on the setting of the trimmer capacitor. This enables it to receive morse (CW), phone single sideband, or amplitude modulated signals with much increased selectivity and sensitivity depending on the setting of the extra Regeneration control. Two or three evenings should be enough to build it! The RX can work on a 9v PP3 battery in the holder or an external 12v mains power supply. You can later add the Ilford Mk 2 CW transmitter. The price of the two band Shipham is £27.
The Stathe RX
This RX is a little more complex to build but is easier to use for reception of amateur phone/voice signals, and Morse (CW) than a Regen. It uses the direct conversion principle but has been kept intentionally simple so that it can be built easily for the band of your choice from 20, 40, or 80m. One set of parts enables use on any one of these bands.
It has a single tuned RF filter for the chosen band that feeds into the SA602 product detector; this integrated circuit also includes the local oscillator stage that works with a second tuned circuit that determines the actual reception frequency. To make it easier to tune, the main tuning is done with a variable capacitor (under the big knob) which works in conjunction with the Fine tuning potentiometer on the right-hand side which acts as a bandspread control. The kit includes capacitors for the oscillator to work on the chosen band. The output of the product detector is amplified and fed to the control on the left which adjusts the audio frequency gain (AFG); with audio filtering selected by alternative part placement, to suit Morse or voice signals. The AFG pot fees the high gain LM386 audio output amplifier that can drive your phones or a small loud speaker.
The PCB is single sided to keep it easy to locate the correct holes for parts and for ease of soldering. If in doubt about which band to build it for, I suggest try 40m, as there is usually more action on that band – but do bear in mind that you might wish to alter it later to 80m to go with the Ilford Mk 2 CW transmitter. The RX can work on a 9v PP3 in the holder or an external 12v mains PSU. The price of the Stathe RX is £31.