OPEN UNIVERSITY AMATEUR RADIO CLUB
NEWS LETTER no:27
G0OUR Affiliated to the OU Club and the Radio Society of Great Britain
Firstly, I will give notice of our forthcoming AGM on Friday 18th January at 12.30pm. As usual, this will be held in the Green Room above the old Lecture Theatre. Please make a note in your diary; local members will be reminded nearer the time. Also a reminder that subscriptions are due on 1st January, and remain at £5 per annum. Cheques made payable to OUARC should be sent to the Treasurer, Fraser Robertson, S1021 Venables Building, Walton Hall, OU, MK7 6AA.
I am pleased to report that back in June we were able to upgrade our main HF transceiver to a (used) FT1000MP. This upgrade was funded largely with money raised at boot sales this year and last year. The new radio is performing very well, and gives significant improvements particularly on the receive side, with a flexible choice of filters, improved dynamic range over the Icom, and a true second receiver facility. It came with the Inrad receiver mod. already fitted, and has most of the optional filters, including an Inrad filter in both IF's.
We are very grateful to the OU Club, who granted us funding to buy the optional filter for the rigs second receiver. The OU club have also granted us money towards changing our amplifier to the solid state FL7000, which interfaces directly to the MP. These are no longer made and have been replaced by the VL1000, which is somewhat out of our league price wise, so we are trying to obtain a used FL7000. We are also grateful to the OU Club for again paying our licence fee, RSGB affiliation, and QST subscription.
At the beginning of November Adrian and Fraser carried out some aerial maintenance work. This entailed dropping down the M100 mast to repair the topband dipole feeder. This had failed once before in the same place, and has now been strengthened to hopefully prevent further problems. While the mast was down the 80m sloper was removed and replaced with a vertically polarised delta loop. A halyard was also fitted which enables us to try out quick temporary wire aerials. Touch wood there have been no problems with the aerials on the fixed mast, except for the lower 80m dipole coming down. Latterly this has mainly been used as a tuned feeder doublet on the 30 and 17m bands.
The 80m delta loop has taken some tweaking to get tuned and matched properly. Originally it was cut for 3.5MHz using the standard 1005/F MHz formula, plus a few extra feet added for pruning. This was fed via an electrical λ /4 of 75Ω coax to transform the nominal 100Ω impedance down to near 50Ω. The loop is fed λ /4 from the top so as to maximise current in the vertical wires, as per ON4UN's Low Band DX'ing book. First off this gave a very low resonance, around 3.1MHz, albeit with a near perfect match. Twelve feet was removed, four feet from each side, which brought the resonant frequency up into band, but the SWR went up to 2.5:1. The feedline was replaced with W103 50Ω line all the way, which made the SWR even worse, so on went the matching section again. Experimenting with an L network established that the impedance at the end of the matching section was around 20Ω. Weird. This needed a small series L and a 1000pF shunt capacitor. Since high voltage / high current 1000pF capacitors are not easy to come by, a 2:1 unun was made. Finally we had a reasonable match around 1.5:1. Thanks to Tom G0PSU for the loan of his W2FMI book which provided the unun design. After all that hard work it was disappointing to find the loop very noisy on receive, due to the racket generated by the OU's UTP computer network. However the delta loop seems very promising as a DX transmitting aerial, and it will be interesting to try it out during the coming winter months.
This year the club station was operated by Linda M0CMK during the RSGB Club Calls Contest. Linda enjoyed her first entry in a contest, except for having to battle with the high noise level. We had a good turn out this year with at least three other members representing OUARC in the contest from their home stations.
The UTP (unscreened twisted pair) computer network that has replaced the OU's coaxial Ethernet, is causing us big problems on receive, in particular on 160m. We also now have a very high noise level on ten metres, possibly from the same source. Unfortunately there is very little we can do about this. Several noise cancelling systems have been tried, but they offer little improvement because the noise is random and not 'point sourced'. On topband and 80m screened loops have proved quite effective against the noise due to their deep broadside-on null, but this approach is unlikely to be of use on 10m.
We have just started on the clubs third log book, which means we have totted up around 5000 contacts, not including those logged on computer, since the club was formed back in December 1990.
The latest news on the move front is that it is still to go ahead, but as yet there are no firm plans as to when. It is now likely that the new library will be built adjacent to the existing field site, so the planned car park extension is on hold. Estates have said it is likely that the field site move will be budgeted in with the new library project. The Security Lodge extension into the field site has recently been completed.
This year we had stalls at two 'boot' sales, the BATC rally at Bletchley Park in May, followed by the DDRC sale at Stockwood Park, Luton. Unfortunately we could not make the Rugby or MKDARS sales due to the dates clashing with holidays and other commitments. However we did raise a total of £186.65 from the two sales. There seems to be a never ending flow of junk in our direction, to the extent that we are now having to be more selective and turn some of it down, as well as having an ongoing clear out of our junk store.
The local AX25 packet BBS GB7BEN closed down in the summer. Dave G4NVB had run it for many years and felt the need to move on to other things. Unfortunately no one stepped forward to take over as sysop so the BBS closed down. The TCP/IP mailbox GB7IMK, also in Bletchley, is still going strong. In his closing statement Dave particularly thanked the OUARC for all it's help in providing forwarding links for BEN over the years. The OU node is still busy forwarding mail, mainly between Bedford and Didcot, Oxon.
The last video was back in April and covered the Dxpedition to Heard Island (VK0IR) in 1997. The next video is 'World at their Finger Tips'. This is an old RSGB video, by John Clarricoats, depicting the growth of the Amateur Radio movement in the UK. It lasts for 45 minutes and will be shown starting at 12.30pm in N2028 Venables Building on Tuesday 22nd January. Everyone welcome.
That's all for this time. Seasons greetings.
73 for now...
Contact: Adrian Rawlings adrianrawlings@googlemail.com