Saturday, February 21, 2009

G8AMU Multimode Receiver

My home built VHF / UHF Receiver (Click image to see full size)
This was one of my most ambitious projects back in the 1980's. Built entirely from scratch, including making the printed circuit boards and all the the metalwork!
Basically the circuit has a 28Mhz front end which is then converted by adding 70Mhz, 144Mhz, 432Mhz and 1296Mhz Converters. Modes of SSB and FM meant having two descrete I.F. strips, one for FM with a TBA120A discriminator and squelch and the other with SL1600 series chips with AGC and narrowband filter. The 28Mhz R.F. strip was mixed down using the state of the art (at the time) diode mixer.
The dial is the famous Eddystone 898 dial, what a wonderful piece of engineering, smooth and lovely to operate, cost me £8 at the time!
The SL1600 series of chips were amazing at the time, I had experimented before using the older SL600 series when I built my 160m / 80m Tranceiver. You could buy these from Birketts at any rally at three for a pound! The SL1600's where a bit more stable and easier to handle, so I bought the ones in my receiver new.
Still think that these Plessey SL chips revolutionised the analogue way of building!
I've got to say that the hardest part of building the receiver was the metalwork. It was built with just a drill, file and hacksaw and took me ages to put together while constructing the circuits at the same time.
The receiver worked well, biggest problem was the audio stage, never could get it right! The receiver is still working and sits in my loft without a power supply at the moment.
I'm really pleased with this project, made me a true Analogue Native!