Several members attended the Thursday evening meeting to listen to Colin G3VTS and Jon M0JMM talking about the construction of their antennas.
Colin who was awarded the G5BK cup at the Constructors’ Exhibition for his 5 band cobweb antenna. He described his cobweb as 5 dipoles in a square shape with 1⁄4 wave sides with the feed point in one corner. The impedance was found to be about 12 ohms needing a 4:1 balun to match 50 ohms coax cable. Colin made good use of a projector and photographs he took during the construction period which took place in his garage and then testing it on the garage roof. He found that the bandwidth was narrow and although no DX was worked, Colin will no doubt be tweaking it leading to further trials in the future.
The second speaker Jon, talked about his 2 metre 3 element Yagi antenna manufactured from a Tape Measure, plastic water pipe, Jubilee hose clamps and a small piece of wire to form a match to 50 Ω coax cable. The tape was cut to lengths suitable for the driven, reflector and director elements, with the driven element cut in half to form the dipole. They were mounted on the plastic tubing to form the Yagi antenna using the hose clamps to hold them in place. At the dipole centre, a hairpin match and the coax cable were soldered to the centre of the dipole. For more information on construction and dimensions of this antenna, look up “Tape measure antenna”.
Jon said that it was ideal as a DF antenna for fox hunts because it was portable, light weight, had a good front to back ratio, a reasonable gain and above all cheap and easy to make.
The talks were well received by the members and it was good to see that the spirit of ‘homebrew’ is still alive !