OPEN UNIVERSITY AMATEUR RADIO CLUB
NEWS LETTER no:24
G0OUR Affiliated to the OU Club and the Radio Society of Great Britain
If there is a red cross at the top of this newsletter it indicates that your subscription for 2000 has not been received. If so, your continued support of the club would be much appreciated. Subs remain at five pounds per anum. Cheques payable to OUARC should be sent to the Treasurer, Fraser Robertson, S1021 Venables Building, OU, MK7 6AA.
The end of 1999 and the beginning of 2000 saw much maintenance work on the club aerials. An intermittent fault on the HF yagi meant it had to be taken down. This was the first time the beam had been taken down since it was installed in January '95. It was quite a major task and many members helped to get it down safely. The fault was narrowed down to one half of one element, but it was apparent that all the connections were badly corroded and a complete overhaul was required. The beam had been originally supplied with copper loaded paste and instructions to apply this to all mating sections. With hindsight it was not a good idea to apply copper paste to an aluminium aerial. All joints had to be dismantled and cleaned, and aluminium loaded paste (Penetrox) was smeared on the mating surfaces. Unfortunately one of the gamma match brackets was broken during re-assembly. A replacement was ordered but got lost in the Christmas post. Eventually a second replacement arrived and the overhaul completed. The first bracket eventually turned up, almost a month after it was posted in Wales. Not bad for first class post!
The beam was re-erected on the 5th January. Again quite a tricky business, eight members turned out to help and everyone was usefully employed. The beam is now working perfectly again. While the tower was down the coax feeding the 30m dipole was replaced since it had water ingress and also the inner core had broken. This dipole was shortened for use on the 17m band because the 17m Bi-square had proved a bit unwieldy with all the other aerial work going on. There is some interaction between the 17m dipole and the beam on 15m, so some further work is needed. A wire was suspended from the tower which will form a 5/8 wavelength vertical for 30m, but as yet the radials and matching unit have not been fitted. The 12m delta loop in the trees continues to work very well indeed.
Having sorted out the existing aerials, attention was drawn to the new portable mast. This required a fair bit of groundwork; putting down and levelling slabs for its wheels and out-riggers, and installing the stakes and guys. An arrangement of parallel dipoles for 160/80/40m was made up and fitted to a stub mast. This work was mostly carried out by Adrian and Fraser, and extended over several weekends. After some careful calculations and adjustments a good match was obtained on each band. We used the technique of folding the ends of the topband legs back on themselves rather than cutting the wire. Even though the wire is insulated, the folded part becomes invisible to RF. As an experiment we cut a length off the ends of the folded sections and it made no difference to the resonant frequency, but folding more wire back did. The final arrangement gives us three dipoles with apex heights of around 120 feet and 100 degree apex angles. The aerials, feeder and stub mast are on loan to the club from Fraser.
As can be imagined the high dipoles perform very well, and some comparisons have been carried out with the existing LF dipoles. Reports from DX stations indicate an improvement of from about zero to 10dB. As expected, the lower the frequency the greater the difference. It was noted that some short skip signals are somewhat stronger on the lower aerials, particularly on 40m. The club station was used by Fraser G4BJM during the FOC Marathon in February, and by Paul G0WAT in the Commonwealth Contest in March. Both noted a very high noise level on the LF bands. One of these days it would be interesting to try to track down its source. The portable mast is due to be taken down in the coming weeks, but we plan to put it up again during the summer, and for next winters DX season. There is much scope for experimentation, and we certainly plan to try out some other LF aerials, most likely some kind of vertical for starters.
The AGM in January went off well with numerous issues being discussed, including safety, boot sales, future purchases, publicity and so on. We agreed to continue our QST subscription. Copies of the minutes are available from Adrian, email: adrian@euroneta.com. At the March meeting of the Field Site User Group we were advised that the long term use of the site is still under review, and part of it may be used to extend car parking as early as this year. Also there are plans to extend the security lodge in our direction, almost doubling its current size. That is rather worrying considering the EMC problems we have had with them in recent years.
There have been some changes to the packet node. We now have a dedicated link to GB7DID in Didcot, Oxon., which replaces the AVN (Chinnor) link. This is working quite well, and also gives reliable Cluster access to GB7DXI in Wokingham, although DXI is moving to Reading in April. We have also established a 9600 baud link to GB7BED in Bedford, although we have reverted to 1200 baud for the moment until a new frequency is found for the 9k6 link. MKPAC have tentatively agreed to fund the radio for this new link, which currently uses a modified Kenwood TM441E which is on loan.
The last lunchtime video was back in January, covering the 1999 Dxpedition to Campbell Island - ZL9CI. The video was made by James 9V1YC who owns a video production company, and so it was of an unusually high standard. We have two short videos lined up for Tuesday 9th May. Firstly, Two Pioneers of Radio - G2DX and G6CJ (22 min.) by the Bristol TV Group, followed by Secret Listeners (30 min.), a BBC account of the work of amateurs during the Second World War. These will be shown starting at 12.30pm in N2028 Venables Building. Everyone welcome.
The main shack PC (486DX66) has been upgraded to have 32M ram. The 286 that was used for packet finally died a death, and has now been replaced with a 486DX50, also with 32M ram and running Windows95. Both PCs were put together from scrap bits and pieces that had been donated to the club. We plan to run Winpack in the shack in the near future. Touch wood there have been no RFI problems apparent with either PC, on transmit or receive.
This summer we have another O.U. Open Day, which will be held on Saturday 24th June. We hope that some of our more distant members will be able to visit and do some operating in the shack.
73 for now ...
Contact: Adrian Rawlings adrianrawlings@googlemail.com