Sunday 14 March 2004

An article was submitted by Ken Tapping, detailing his experiments at 4 GHz. This can be found in Projects section here. It is about 1.2MB in size and is in PDF format. See below for the Introduction.


Some years ago, someone found they could receive the signals in the 3.7-4.2 GHz Band (C-Band), which is used by broadcasting companies to transfer programme material. This led to a flowering of back garden 10ft and 12ft dishes, mainly in North America, as companies started to sell domestic satellite TV systems to receive this signals. Of course, this free distribution of broadcasts was not what the broadcasting companies intended, and they started to scramble the transmissions. There then followed an arms race between the broadcasters and manufacturers of descramblers . This ended with the introduction of formal broadcasting from satellites, but at a much higher frequency, where domestic satellite receivers only need antennas about 2ft (60cm) or so in diameter.

The C-Band satellite TV market collapsed, leading to relatively state-of-the art receiving equipment becoming available free, or at most, for junk prices. One of the first people to realize that this equipment could be used for a wide range of radio astronomical experiments was Bill Lonc, of St Mary s University, Halifax, Nova Scotia, Canada. In his book Radio Astronomy Projects he describes experiments done with the participation of undergraduate students. These were usually aimed at solar observations, or in a few cases, observations of the Moon. With his assistance, Heather Cameron in Nova Scotia used such systems for single-dish and interferometric observations of the Sun.

For a long time I had no plans to do anything in this frequency range. However, a couple of years ago this changed, thanks to a friend, Tony Zonta, who was (Tony died last year) an avid amateur astronomer. To fund his hobby he ran a pub and small hotel. Tony s pub produces the best pub food in Penticton, and one day, my family and I were enjoying some of this, when Tony joined us. During the conversation he said that he had asked a radio astronomer if one could make a radio telescope out of old C-Band satellite TV equipment, and had been told No . Did I agree with that? I said no. I knew of many examples of radio telescopes having been made out of old satellite TV equipment, Bill Lonc s experiments for example. His reply was There s one on the roof. It s yours!

With a lot of help from Tony, we got the 10ft dish and electronics to our (fortunately) large back garden. Experiments with this led to my getting very interested in the possibilities offered by such cheap but high quality equipment, and led to the series of experiments which are described in this article.