At the meeting of the LRS on 28th March 2012 LRS Past-President Dr. John Cooke GM8OTI talked about "Homebrew Microwave Construction". John is an avid SOTA operator and has designed and constructed all his lightweight portable equipment, progressively moving up in frequency band, now on 13cm. When first licensed in 1978 John wanted to get into microwaves. After returning to the hobby a few years ago he's finally got there. John wants to convince others that building microwave equipment is nowhere near as difficult as some people like to make it sound!
John described his progression through many microwave projects and construction techniques. These started with a local oscillator on 48 MHz multiplied up to 864 MHz to provide a 432 MHz output on 1296 MHz. Etching techniques for his PCBs initially used indian ink as a resist and then enamel paint; lately he has used adhesive tape and photographic techniques. A 0.5W PA was added to the 23cm receive converter. After various tests, local beacon 23cm GB3EDN was received! Other projects included a wavemeter and a 23cm yagi antenna to the DL6WU design, using PVC tube and 15 metal elements. The first PA was not a big success, and was replaced by the "PUFF" PA running 0.25W. John's first successful QSO was with GM4JTJ in Arbroath.
The second major project was a 13cm transverter, based on learning gained in the successes and less-than-successes with the 23cm transverter! The GB3CSB beacon was heard from Cairnpapel Hill and many QSO have now been had on this band. A near-miss was when OZ1FF in Denmark was heard but not worked - tsk!
John is now working on a 3cm transverter. He found a Gunn diode that has been in his junk box for many years (decades?) and has configured it with a waveguide unit.
For more information, go to John's own website: http://www.marwynandjohn.org.uk/amateurradio.html
John with his 23cm & 13cm transverters and yagi antennas
The 23cm transverter, consisting of several interconnected units.
The 13cm tranverter in its more compact cabinet and the 13cm yagi
Close-up of the 13cm transverter - nice work!
John shows his 23cm yagi to an enthralled Andy MM0FMF.
John's portable 2m diameter dish for 23cm and 13cm - all done by calculation!