17th April 2008 at St Helena School

The meeting opened with a report from Bill 2E0BMG on the latest progress in the preparation of the Club QSL card. A final draft is expected at the next meeting. The Chairman Kevan 2E0WMG announced that Brian G0GGM had resigned as Training Co-ordinator. This is a key post for the Club and it is hoped that a replacement will be found very soon. A letter of thanks will be sent to Brian.

Bev G0KOY was introduced to members in his new role of Equipment Manager, although not in attendance at the meeting Mick M0DEQ was also welcomed to the Committee and is expected to take his place on the Executive Committee at their next meeting. The domain name for the club website is www.g3co.org.uk and various people are involved in its development.

The Colchester Normans Cub Group based at Stanway have invited the Club to give a demonstration of Amateur Radio on a Tuesday evening later in the year. Members were reminded that the Dunstable Downs Amateur Radio Car Boot Sale be held on Sunday 18th May at Stockwood Park Luton and that a rally was planned at Ipswich on 15th June (see page 4 for further details, Ed). The Wetzlar Net would be held on or near 7095kHz on Sunday 20th April with DL2DN, Herbert and G3FIJ, Frank as net controllers.

The Chairman then invited Alan, G0HKG to explain the construction and operation of the ZL Special beam aerial. Alan opened his remarks with a note of uncertainty regarding the origin of the name of this aerial, the most likely explanation was that it was developed in the Antipodes...New Zealand. Alan then referred to the well known magazine author Fred Judd, G2BCX who had written many articles in Practical Wireless about this aerial as being compact and neighbour friendly but packing a considerable punch with a 12 element version giving a gain of 14dB over a dipole all with a 10ft boom. The aerial gain figures were described. dBd and dBi were regularly used in advertisements with the dBi value being 2.3dB greater than the dBd value. The two driven elements were largely responsible for the enhanced gain over a simple Yagi aerial. These were folded dipoles with the rear one slightly longer than the inner one which ensures that the aerial has a good front-to-back ratio. As a horizontal aerial the ZL Special would normally be mounted at its balance point at the centre of the boom, but for vertical polarisation the beam should be mounted either on a fibre glass mast or held by the end of the boom to a metal mast.  

Alan concluded a very interesting talk with hints and tips on aerial construction and particularly the need for accuracy in cutting elements to length and taking account of the material, size of the boom and diameter of the tube used for the element when calculating the length of the elements. The length of the phasing line between the two driven elements was also critical and a 1:1 balun was essential at the feed point.

Alan also reminded members that the Wrotham Beacon provided a very stable and strong signal for measuring aerial performance. GB2VHF is on 144.430MHz. Thanks Alan for a most enlightening talk which should inspire many members to have a go at building their own beam aerials.