No Meeting today.
‘The Event’ was the simple way Stewart’s wife Marie referred to the 2012 SOAB SSB CQWW Contest entry which they planned to do on the Isle of Man. Stewart, G3RXQ was going to operate, ably assisted in setting up the station and domestic support by Marie. It became clear that Stewart had put a lot of time into the planning, even to the point of using computer schedules of events prior to packing, setting up and operating.
In May 2012 Stewart and Marie had visited the island on holiday, and whilst there went looking for a potential site from which to operate a contest. A site was found and the arrangements were made with the owner.
A plan of the site was produced showing where best to site the antennas. A portable HexBeam was used to cover 20,15 and 10m. Two phased verticals for 40m, together with a Doublet fed by open wire feeder for Top Band, 80 and 40m also provided good capability. In addition there were Pennant antennas to help with reception on the lower bands should they be needed. On the equipment side 2 transceivers, a linear amplifier, antenna matching unit, five large reels of cable, the operating table, PC and two computer monitors were all carried in a small van by ferry to the island.
The contest went smoothly, helped by unexpectedly good weather. The only real problem, was although Stewart had been assured there would be chairs a plenty in the bungalow, none could be found that were at all comfortable! (Note: put favourite chair as first item on next year’s list)
In spite of the discomfort, the score looks pretty good: First place on the IOM, about 64th out of 385 stations in EU and about 157 out of 958 world wide. The final scores have yet to be published.
On the subject of final scores, Stewart noted that it is worth checking the published logs to what see what Band Strategies the winning stations employed during their contest.
So, all in all a good contest, in spite of the chair…
Don, G4LOO, spoke of Phased Array Antennas and we were surprised to find there were so many types. Some for over the horizon radar, some for enhanced reception, some for shortwave broadcast, but the type of most interest to us was the four square vertical.
Don described how he built a 40M system based on fibreglass poles held by short aluminium supports. The poles hold a quarter wave wire, helically wound. Each vertical has 32 quarter wave radials and at the point where the radials would have crossed at the centre of the configuration, they were instead, connected to a bus wire. Each of the verticals are connected by coax so that the signals can be switched to be either in phase or out of phase to either enhance the signal or suppress it.
Of the four types of switching systems described, Don built the Collins Hybrid Phasing System.
The overall antenna is expected to give a front to back ratio of well over 25 – 30dB depending on the incoming signal angle. The noise level on the antenna is also much lower than that of a single vertical and the beam switching can be done in a second!
The AGM was opened at 8pm. Various reports were submitted and the new officers and committee were elected. A list of which can be found in the Forum. (Go to Forum > The Club > The Committee). The election of Auditors will have to be determined later and agreed at an EGM. A vote by ballet was taken to select the ‘Best talk by a Member’ and the results will be announced when the cups and plaques are awarded at the Club’s annual dinner on the 20th of April.
It’s enough to strike terror into the hearts of many radio amateurs who had to learn how it worked and how to use it.
However, Stewart, G3RXQ showed that it’s not quite as complicated as first thought and the results can lead to an efficient antenna that really ‘gets out’. Many amateurs are lead to believe that buying an ATU, or more correctly, an Aerial Matching Unit, can solve most antenna problems just by presenting the transmitter with a 50 ohm load. These units might be more correctly called ‘Transmitters Tranquilizers’ since they do nothing to tune your antenna, only keep the transmitter happy, while the un-resonant antenna at the other end of the transmission line might be wasting up to 95% of the power presented to it, leaving only a few watts for actual transmission.
By using an ‘active’ Smith Chart, Stewart showed how the situation could be visualised and also what was needed at the antenna end in the way of capacitance or inductance to match the antenna impedance, thus using almost all the power for transmissions.
The ‘active’ Smith Chart can be found on the internet at: http://science4all.nl/?Electronics::Pasan This excellent programme was written by Marien van Westen (PA0MVW) and offered, free of charge. It brings the Smith Chart of 1939 right up to date!