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Chelmsford Amateur Radio Society

CARS Meetings January to March 2010

Award for All
12th March 2010 Added/amended the March Meeting report.

January Meeting was Cancelled due to snow and Ice.
Rescheduled for March.

February Meeting:-
"The Loop Fed Array" Yagi".
By Justin Johnson, G0KSC.

Continuing our Aerial theme from February last year when Tony, G4YTG presented "Amateur Aerials", Justin presented an Amateur Construction talk based on his professional designs of Yagi Aerials.

It was a dank, cold night but thankfully no snow or ice but the hall was full to the extent more chairs had to be produced.

G0KSC Presentation
Chairman John opening the meeting.
Photo by Trevor, M5AKA

Chairman John welcomed CARS Members and a number of visitors including Chris Street, 2E0FPE, Secretary of the North Wakefield Radio Club, Dave Gould, G3UEG and G4YBN from Harlow.   CARS Meetings Secretary, John Yates, G1UZD looked after a visitor from New Zealand but at the time of writing, do not have a name or call-sign.   Assistance was also given by Bob, G4MDB - thanks.

G0KSC Presentation
Justin, G0KSC and John, G1UZD; CARS Meetings Organiser.
Photo by John, G8DET.

G0KSC Presentation
G0KSC opening slide.

Justin reminded the large audience of the typical charateristics of a Yagi Aerial.

G0KSC Presentation
Following slides taken with permission of Justin.

He then went on to explain the advantages of the LFA.

G0KSC Presentation

G0KSC Presentation G0KSC Presentation
What does one of Justins Aerial look like?

Justin has considered the lateral thinking of mounting the Folded Dipole in the same plane as the Reflector and Directors.   This reduces the wind loading and changes its characteristics.   It is essential to have a very good computer modelling program - too complex to do it emperically.

G0KSC Presentation
The Soft Aluminium Bender used to bend the corners of the Dipole.
They are spot welded in position once the design is stabilised and proven.

G0KSC Presentation
Justin prefers that all elements are isolated from the support boom
as this lowers the changes due to temperature, damp, snow etc.

G0KSC Presentation
Pawsey Stub matching unit.

G0KSC Presentation
The near perfect match obtained with Justin's design.

G0KSC Presentation
A 2 Metre Aerial which Justin brought to CARS.

G0KSC Presentation
Left to right - 2 visitors from Harlow and Chris, Sec of the North Wakefield Radio Club.

G0KSC Presentation
Left to right - "Wakefield" Chris and Dave Penny, G3PEN listening to Justin during the refreshment break.

G0KSC Presentation
Another group looking at the LFA.

G0KSC Presentation
Close-up of the LFA - notice the Welding Brackets used to isolate the elements.

G0KSC Presentation
Picture of the 70MHz LFA Aerial.

G0KSC Presentation
Feed of the 70MHz Aerial.

G0KSC Presentation
Murray telling the audience about the GB75CH Event from Great Baddow on February 27/28th.

Thank you Justin for a nice and technical subject put over in a relaxed way such that people could follow it.   All we have to hope is that a few people feel they can build a LFA.

The high quality Raffle was organised by Peter Graves, G0KSJ - thanks.
There were some good prizes - a few won by our visitors.

Door duties were by John Yates, G1UZD. Colin, G0TRM provided the Audio System - Thanks to both.

March Meeting - "Modernisation of the London Underground"
By Mark Sanderson, M0IEO.

A large audience was welcomed by Chairman, John who started by asking President Harry, G5HF to present the Certificates to Richard and Peter Medows for their winning entry in the Constructors Competion during 2009.

Presentation of the Constructor's Competition certificate
Presentation by Harry, G5HF of the Constructor's Competition certificates to Richard and Peter Medows

London Underground Logo How many of you have used the underground railway in London either to get to work or at the weekend for a day out in London?   This was the first question Mark posed to the Meeting.

This was followed up with "Have you ever stopped to wonder how the system, which was first opened in 1863, is kept running?   How is maintenance carried out on tunnels, which in places are nearly 150 years old?"

Mark explained that as the infrastructure grows older it requires more work to keep the system running and with the eyes of the World being cast on London in 2012 with the Olympics coming to town, it was time to spruce the Underground up and bring it up-to-date.

The showcase of the underground is Oxford Circus station which is completed on time in January 2010, brought to the end of an planned £80 Million (out-turn at £125 million) refurbishment.

The main thrust of his superb presentation was with the station open to the public from 06:00 to 00:30hrs seven days a week, how does the work get done?

After the Break during which Mark answered questions and the Raffle was Drawn, Murray, G6JYB showed pictures "off air" of the GB75CH Radar event which occurred the previous weekend.

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