THE CATSWHISKER - NOVEMBER 2000
Newsletter of the South Dorset Radio Society
Editor - John Rose, M0BQO - 45, Ringstead Crescent, Weymouth, DT3 6PT, UK
You can e-mail John at: m0bqo@g3sds.org.uk
SDRS NEW YEAR LUNCH
Our New Year lunch (the 'Alternative Millennium!') has been booked to take place at the Glenburn Hotel, Preston Road, Weymouth, on Sunday January 14th 2001, sitting down at 1pm.
Since the last SDRS lunch some years ago we have lost a few old members and gained quite a few new ones. It seems appropriate now to mark a phase in the Society's development (2001 being the year of its fortieth anniversary) and celebrate our recent successes in several fields of achievement.
Hopefully all members will make a very special effort to attend. Guests, friends, XYLs, YLs, etc. will of course be very welcome.
The Guest of Honour will be Phil Mayer, G0KKL from Poole an RSGB training officer for Dorset over many years.
The cost will be £11-95 per head.
It would be helpful at this stage to have some idea of numbers - there seemed quite strong support at the October club meeting - The menu will appear in the December Catswhisker so we will be able to collate your selections during that month.
An early confirmation would be helpful; please tell John, M0BQO or Robert, G0RYL as soon as possible.
GOOD VIBRATIONS - www.g3sds.org.uk
The SDRS Web Site has gained a lot of fans. One is Murray Ward, G3KZB, author of the Questions and Study program used in our RAE course.
His letter to Neville was most complimentary and he wishes congratulations to be extended to Geoff, G0EVW for it.
You can download the excellent free program from Murray's Web Site: http://freespace.virgin.net/murray.g3kzb/
Also check out the latest links and downloads on the site contents page.
MORE SUCCESS!
The Novices course, at the QTH of Neville 2E1HFY, has produced three more passes - Kyle Roff, Bill Neill (2E1HZP) and Owen Morris (2E1OZY).
The Practical Wireless QRP contest resulted in SDRS gaining 14th place out of 87 and first out of five in this area. Thanks Pat G1XJH and the 'dream team' - see below.
DATES FOR YOUR DIARY
Club Meetings
Please, all members and readers, try to publicise these meetings far and wide because they are all worthy of special attention.
Nov 7th - Rev. Alan Rogers' address is entitled "Fishing in Murky Waters". He was a codebreaker at Bletchley Park during WWII; already the prospect of his address has excited a good deal of interest and we can expect a few guests as it has been publicised outside. but as far as the title is concerned, well, all I can say is it must be truly enigmatic!
If any of our non-member readers intend to come to this meeting, or if any member intends to bring guests, would you kindly let John, M0BQO m0bqo@g3sds.org.uk know so that we can arrange sufficient accommodation and refreshments?
December 5th - A member of the Radiocommunications Agency has been booked, and the subject is 'The History of the Radio Investigation Service' though undoubtedly topics will spread far and wide around that theme.
January 2nd - Annual Quiz. This time, Robert G0RYL and Carol have one for us to enjoy
January 14th (Sunday) - SDRS Club Lunch.
February 6th - Demonstrations of Digital techniques including Packet Radio, UI-view, WX satellites.
March 6th - Bring-and-buy sale. Please note change.
April 3rd - SDRS Annual General Meeting.
RAFFLE PRIZES
Our monthly raffles are proving popular but it is always the Committee members who are providing the prizes. It would ease this burden if some members would care to donate a prize - no need for an elaborate or expensive one. Any volunteers?
CHARGES FOR REFRESHMENTS
Carol does wonderfully in providing refreshments but can't do it free of charge. There has been a shortfall. Maybe you didn't realise that's what the jangly cup was for! Therefore we will have to ensure that everybody, members and guests, pays at least 50p to cover the cost and any excess will go to club funds.
HF AERIALS - Rob Micklewright G3MYM
Those fifteen who attended October's Club Meeting were treated to a scholarly lecture by an acknowledged authority on the subject of Aerials.
Robert carefully explained how your success (or otherwise) may depend upon the type of aerial you use, the environment in which it is situated and the position you place it in. Then, assuming you have the right one at the right place, factors such as impedance, radiation pattern, power gain and efficiency come into play.
There are seven different components that combine for the impedance, being a complex arrangement of resistive, reactive and inductive forces. An important one is the inductive field loss if the aerial is too low - the ground absorbs some energy.
Robert explained how propagation lobes form at heights below a wavelength. If you can make the aerial high enough - 1 wavelength - it can produce good lobes at 15 degrees which aid propagation.
He also described the effect of Ground Constants - i.e. the type of ground you are transmitting from. A station in a marshy valley is much better than one at the top of a rocky hill.
As a general guideline, an aerial should be as high as possible, straight, and in the clear. He applauded the American notion - make it as long as possible and tune for resonance.
G5RV - doublet or dipole?
Answering the Eternal Question, Robert explained deeply how a Dipole differs from a Doublet. The G5RV is probably a doublet on top band, but a dipole on all others. As with so many aerial questions, the answer begins with 'It all depends what you mean by'.
LIMPY ARNOLD
Robert recognised the aerial 'Limpy Arnold' featured in a recent Catswhisker (September) as in reality a skin-effect dipole or controlled feeder radiator. It's a clever design that uses the skin effect of a braided outer covering of a coax lead to form a dipole. (It has been developed over recent years and is described in the latest ARRL handbooks.)
It was one our Dutch friend Geert made up from a description and hung on his yacht's mast to use at 2m and 70cm. In fact this relative newcomer has been around since 1991. It uses the well known 'skin effect' phenomenon in a novel application, using perfectly ordinary coaxial feedline cable.
Why skin-effect? In a co-axial cable, the braid shielding has two surfaces - inner and outer. Current can flow one way along the inner skin, and in the opposite direction along the outer skin.
When the transmitting current flowing through the central conductor reaches 'free space' - i.e. it is clear of its shielding - it radiates out as normal.
But that in the braid's inner skin has nowhere to go except back along the outer skin. So, to the outside world it looks like a dipole with current flowing away from the end point of the braid in both directions.
How far back does the current-rich braid go? About quarter of a wavelength, where it is coiled into an RF choke effectively terminating that end of the dipole.
It's known as a Resonant Feed-line Dipole in the ARRL handbook and has the advantage of not requiring a separate aerial and fixtures as it's all part of the co-ax feedline, making it particularly handy for portable operation. The Handbook gives dimensions for various bands. All you have to do, you avid aerial constructors, is to find some way of stripping off up to sixty feet of coax braid!
RF Choke dimension (approx)
On 80m, 20 ft of cable with 6-8 turns. On 10m, 4ft with 6-8 turns.
THE PW QRP CONTEST
From Pat, G1XJH
The venue was at Hardy's Monument IO80RQ.
The date was the 18th June 2000.
The callsign that was used was GX8SDS/P the clubs VHF call.
Start time was 0900, end time 1600
The class that was entered was single ant. multi op.
EQUIPMENT USED
ICOM IC746
10M MAST
ASTATIC TEARDROP
OUTPUT 3W.
QTEK 13ELE YAGI.UDI
CALLSIGNS AND OPERATORS ON THE DAY
GERRY, 2E1IPZ
ROBERT, G0RYL - THE STATION MASTER
MARK, M1EPD - 50% ULTIMATE
RICHARD, 2E1HSI - THE NIGHT WATCHMAN
PAT, G1XJH THE OTHER - 50% ULTIMATE
CAROL, SWL -THE ULTIMATES SLAVE
Assisted by ASHLEY, SWL
The day started off warm and calm, at 0600 I watched Mir pass across the moon.
I thought that this was going to be a great day! At about 0800 the station was erected and the initial pre-contest calls were made.
The conditions were great with Belgium, France and Sweden just to start the day off.
There were many visitors from afar, cb'ers and amateurs alike just to see the station up and running. Carol did a great job with the food as normal. During the afternoon the wind started picking up and it was decided that the ant. had to be lowered. So the signals dropped by about 3db but the enthusiasm was not altered The operators kept going to the end. The results were sent off and we all waited with bated breath for the results.
Well the results have turned out great!
GX8SDS/P CAME
14th OUT OF 87 LOG BOOKS ENTERED.
IN OUR AREA 1st OUT OF 5.
Single ant. 11th
Multi op. 11th
SO ALL I HAVE LEFT TO SAY IS WELL DONE EVERYONE THAT JOINED IN TO MAKE A GREAT DAY OF THE PW CONTEST AND THANK YOU TO THE VISITORS THAT CAME.
Hopefully see you all next year, 73 de Pat, G1XJH
SDRS 'DREAMTEAM 2000'
MAST FOR SALE
The late Bill Dean's (G0NRQ) aerial mast is for sale. It is believed to be an extendable tilting lattice mast.
For more details please phone Janet at 01305 788578.
SPARE A THOUGHT
Emma, M1CCJ the SDRS hon Treasurer has been rather poorly and has spent some time in hospital.
Neville, 2E1HFY has mobility problems which are causing him to miss meetings.
Ray, G1YRS on Portland is very poorly.
Ken O'Brien in Dorchester is still having to take things easy after his by-pass operation.
Dave O'Brien of Preston is due in hospital any time now for limb surgery.
We all send our best wishes to them with hopes of a speedy recovery.