The “Skills Evening” held on 18 October proved to be very popular, with one of the highest attendances so far this year. Six members manned tables around the room to demonstrate, explain and talk about an aspect of amateur radio – usually one which was a particular interest of theirs. Ken G3LVP explained how make properly make-off coaxial connectors such as BNC and N-type, with examples and supporting diagrams. Peter G3YJE demonstrated a “Tuna-Tin” QRP transmitter, showing the output waveform on a ‘scope. He was also promoting the American Radio History website to which he has been contributing for several years. Paul 2E0IFV had a display of DMR radios, including hand-helds, and demonstrated their use. Tony G3SNN showed his fine collection of exotic QSL cards for his 160m and 6m activities. Barry M0HFY had a live demonstration of FT8 (one of the latest data-modes which is currently very popular), making several contacts during the course of the evening. Mike G4GUG was extolling the virtues of Linux, and telling how well this Operating System would run on older machines. Each of the tables attracted a gathering of members for much of the evening, and much general and lively chat took place as well. Very many thanks to the six members who kindly “volunteered” to man the tables and indeed to everyone else who made an appearance; you all contributed to the undoubted success of the meeting. We were pleased to enrol Chris M6NZC as a new member and John 2E0GCR who re-joined after an absence of a year or two. Thanks once again go to Alan M0NRO for kindly manning the kitchen. Thanks also to the several members who, without being asked, helped clear away the tables and chairs at the end of the evening – your efforts are much appreciated.
CARA will be running a Foundation Licence course over the weekend of 19th and 20th January 2019, followed by the exam on Sunday 27th January.
For further information please email Barry at firstname.lastname@example.org
The next CARA meeting will be held on Thursday 18th October at Brizen. Doors open at 7pm for an 8pm formal start.
A Skills Evening – tables will be set up around the room with the following demonstrations: DX QSLing – Tony G3SNN American Radio History website – Peter G3YJE. Looking at the output of a Tuna-Tin QRP tx – Peter G3YJE. Making off BNC and N type connectors – Ken G3LVP and Giles G0NXA. FT8 – Barry M0HFY. Linux and some apps – Mike G4GUG. Come along and learn about something new and enjoy a good chat to fellow members. Tea, coffee and biscuits will be available as usual.
We are very please that Tim G4VXE has kindly agreed to return to the club to present another of his talks, this one entitled “UnRealRadio”. He’ll be telling us about Network Radio, how it works, what equipment is needed and how it’s used. He may, if time permits, also talk about Digital Voice radio. Tim used to live in Cheltenham and was a very active member of CARA before leaving the area. He writes regularly for Practical Wireless and will soon also be writing regularly for Radio User. Network Radio is a somewhat controversial subject among radio amateurs, some feeling that it’s not true amateur radio and it “shouldn’t be allowed”, others that it’s something new and exciting and may well be a useful facility for encouraging new recruits into our hobby. Whatever your views, please respect what Tim has to say and listen without over reacting. Thursday 20th September, 7.30 for 8pm at the Brizen Centre, Up Hatherley Way. Visitors and prospective members will be made welcome.
The UK military Wireless Set No 19 (WS19) was manufactured in great numbers for WW2 and used extensively during the war and in the years after. It appeared on the surplus market in the 1950s and 1960s and was used, often after modification, by radio amateurs to get on the air – in those days there were no “black boxes” from the Far East and what commercial gear there was, mainly from the USA, was very expensive. These days the set is sought after for restoration.
At our August meeting Tony G3YYH will tell us more about the WS19 set and how in recent years he has restored one to working use. He will have his set on display and, hopefully, working. This will be an interesting meeting whether or not you are a military wireless buff!
Visitors and prospective members will be welcomed, as always.
Thursday 16th August at the Brizen Centre, Up Hatherley Way. Doors open by 7.30 for an 8pm start.
The Brizen Young Peoples’ Centre is located between Morrisons Superstore and the Shurdington Road. Beware of the height barrier when entering the car park.
Last month we were pleased to welcome back Peter G3RZP, a well known speaker at amateur radio functions – at local, national and international levels.
The title of his talk was “Clean Signals” and he proceeded to tell us why transmitters, and SSB transmitters in particular, emit signals which are much wider than they should be – and so cause interference to stations on adjacent frequencies. SSB transmitters are essentially “linear” amplifiers, amplifying a signal generated at low-level up to the desired power required for transmitting a signal to wherever. However, the amplification process is not actually truly linear because of the inherent characteristics of the active devices, be they thermionic valves or solid-state devices. In an SSB transmitter the non-linearity gives rise to what are known as “intermodulation products” which spread out either side of the main signal. Intermodulation products are, in the simplest case, caused by two discrete signals being amplified mixing together, because of the non-linearity, to produce low-level signals spaced from each other by the difference in the frequency of the two signals. The further away from the main signal the weaker these products become. But even low-level “spurii” can cause QRM to near by stations.
So the way to minimise such interference – sometimes called splatter – is to make the transmitter/amplifier operate as linearly as possible. This can be done by making sure that the equipment is not over-driven – ie by not turning the mic gain up too far, by using minimal amounts of ALC and by making sure that the transmitter sees the correct load impedance. In the design stage negative feedback can be introduced to improve linearity, but this can cause other problems if not done carefully. One way to check that the transmitter is being operated corrected is to inject two audio tines into the mic socket and look at the RF output with a suitable ‘scope, the tops and bottoms of the waveform seen should be nicely rounded. Peter’s view was that in general valve amplifiers are inherently more linear than solid-state ones.
The talk was well received to judge by the number of questions asked. Many thanks to Peter for travelling from Swindon to see us once again.
How clean is your transmitted signal? What is meant by a “dirty” signal? What causes a dirty signal to be transmitted? What are “inter-modulation products”? Do you know how to adjust your transmitter so that the PA is not over-driven? For the answers to these and no doubt many other relevant questions come along to our July meeting to hear Peter Chadwick G3RZP talk on the subject of “Clean Signals”. Peter is a well known and highly qualified engineer who has given many talks to clubs over the years – including CARA. He has served as a technical advisor on national and international committees, eg IARU and ITU, so knows his stuff! We are pleased to welcome him back again for another of his thought provoking and informative presentations. Please attend and make his trip from Swindon worthwhile.
7.30 for 8pm on Thursday 19th July at the Brizen Young Peoples Centre, Up Hatherley Way – located between Morrisons and the Shurdington Road.
Beware of the height barrier when entering the car-park.
Coffee, tea and biscuits should be available as usual.
Visitors and prospective members will be welcomed, as always.
A good turn-out of members enjoyed an interesting display of exhibits from members’ radio rooms (or shacks if you prefer!). The exhibits ranged from early types of detectors of radio signals to a modern piece of kit to power radios from solar energy. Also on display were a selection of old QSLs cards, an Elecraft Miniature ATU, a once popular IC-202 portable 2m SSB rig from the past, a Retevis RT82 DMR hand-held, a portable station in a box and a dog! To add further interest to the evening Mike G4GUG gave a short talk on how to set-up a rotator for satellite working.
Many thanks to everyone who brought along something to show, to Mike for his talk and to Peter G3YJE for manning the kitchen (yet again!).
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 !
The meeting started with a mini-auction of kit from the shack of the late M0ITF. There were bargains to be had and several members went home with some useful goodies. However the reserves were not met on the more valuable lots so these will be sold by other means, including rallies. Many thanks to everyone who supported the auction, and particularly to Mike G4GUG for doing a super job as the “porter” holding up and describing the various lots.
The second part of the meeting was a session by Barry M0HFY on PSK. He spoke about the various forms of this particular data-mode and illustrated how it could be used with the HRD logging program. A very interesting talk, supported by good screen-shots, even for those like me with little or no intention of trying the mode! The talk greatly improved our knowledge of PSK and we’re very grateful to Barry for his time and trouble.
A brief survey of members’ opinion on the suitability of the venue for our regular monthly meeting indicated a preference to remain at Brizen.
Thanks also go to Colin G3VTS for manning the kitchen.