11 July 2019 – RF and Earthing by Richard, G3Nii

It became apparent right from the start that Richard’s talk was not for the un-initiated. Quoting directly, Richard said:  The earth provided by the electricity supplier is intended as a protective part of the circuit to reduce SK membership, as well as protecting devices and equipment attached to the supply.  It is a very important part of the circuit that has to comply with various parameters as set out in the 17th Edition of the IEE Regulations, BS7671. The 18th Edition is now replacing the 17th, this may result in further adjustment of the earthing requirements. Over the years the way in which the earth connection has evolved and is provided has seen changes and indeed variations for different types of consumers, e.g. industrial, farming, those supplied by over-head lines and domestic users.

Richard continued with a description of the mains supply from the sub-station to the supply into the property.  He described various methods of earthing used in the past and finished with the TN-C-S system (PME) used in the majority of properties today that offers the biggest challenge to incorporating an RF earth and where extreme care needs to be taken.

Richard then pointed out a potential problem which was highlighted in an article by Peter Chadwick, G3RZP, well known for his many presentations at RSGB conventions, highlighted in a RadCom article in 1980 the possibility of a failure of the neutral  of a PME supply system  that could lead to a disastrous situation arising, a situation that can and has arisen in the past. So although a rare possibility of it happening take careful note of the consequences should it do so and the procedures necessary to avoid a catastrophe.

Many Radio Amateurs will have their RF earth attached in some way to the general earth wiring of their house mainly due to their not understanding any of the  limitations or requirements associated with doing so. It is a very dangerous path they tread.

Richard continued; So what’s to do? Do you really need an RF earth ? Insulated radials, above ground, or a counterpoise arrangement for those antennas needing an earth, both would work well. Many claim that the counterpoise is quite superior to radials  But, if you have a tower you will no doubt want to protect against high static charge build-up and electric storms thus needing an earth point close by. However, consider a lightning strike yielding 100MV and 200kA, this obviously will destroy everything in its path. A near discharge could be tolerated by a good supplementary earth point, but don’t rely on the PME earthing for this purpose.

Other things that could be done included completely isolating the shack, but that must comply with regulations, or a large isolation transformer, apart from the cost, might an answer.

More info can be obtained from the RSGB. Search for their EMC07 Advanced Leaflet titled Earthing and the Radio Amateur.

 

 

 

 

 

 

 

 

4 July 2019 – This year’s club project

Richard, G3NII explained the main purpose of the latest club project, an HF choke, is to stop common mode currents flowing on the outer skin of coax feeder thereby stopping radiation from the feeder, stopping RF from getting back into the shack and also to lessen QRM pick up on the coax feeder. Thoughts of where if should be placed indicated that since this was adding impedance to the circuit, then positioning in the shack would be worth considering – BUT, make sure the feeder is not an odd number of 1/4 wavelengths long, any number of 1/2 wavelengths long would be ideal.

Richard pointed out that the project required 12 turns of coax on the toroid. You have the choice of 5 turns then cross-over then 6 turns, alternatively 6 turns then cross-over then 5 turns. The cross-over counts as one more turn.

The kits, which included all materials required, including the box,  were handed out and members started the winding and fixing. The evening ended with a Q&A session about the choke and other antenna configurations.

The kits were supplied to members only

Winding details

Planning for IARU contest – Paul, G1GSN

As last year, Paul is hosting a ‘mini’ contest for members who want experience in contest operating outside the usual high profile and high pressure atmosphere. The venue will be the same as last year. Paul detailed the aerials which he will erect and the equipment to be used.

The contest is a 24 hour test, running from 13:00 BST start on Saturday, 13 July to the end at 12:59 BST on Sunday 14 July, with the exception of our shut down over night, I.E. 10PM to 9AM.

So, here’s a good chance for members to get some practice in contest operating in a relaxed atmosphere.

20 June 2019 – A Planned approach to Dxing – by Ken G4YRF

The presentation started with a look at sites giving up to date details of planned DXpeditions so you know when the operations should be starting. Then sites used to find real time information of the stations operating. That was followed by sites to let you know who in the world is actually working the DX and if there are G stations going through, if so, Work them yourself!

6 June 2019 – The micro car by David Wherrell

Messerschmitt KR200

David began by describing the parallel universe of cars. ‘Ordinary cars’ had four wheels, usually designed with the family in mind to travel in comfort. While the Micro cars were usually powered by cycle engines and had three wheels. Cost wise they represented minimalist motoring.  In fact, some early cycle cars were pedal powered!  One even invited passengers to join in on the pedals!

Numerous small car models were described like the three wheeled Morgan from 1909 followed by improvements in 1925 of the Morgan Aero and then in 1949, the F-Super. Dozens more cars like the Reliant, the Bond Minicar, 1953-1968, the Berkeley, manufactured in Biggleswade from 1956 to 1960 were described.  From 1953 to 1964 Messerschmitt made the famous KR200 three wheeler powered by a 200cc 2-stroke engine. A total of 30,286 were built!

In 1953 the Italian designed Isetta arrived on the market. Eventually, in 1955 BMW acquired the license to build them.. This popular model bosted a 300cc 4-stroke engine. Originally a four wheeler, it was changed to three wheels to benefit from lower road tax in Great Britain. A British version was produced in Brighton from 1957 till 1964.

Numerous other small cars were discussed finally arriving at the present time when it was revealed micros were still being produced in France, including the Daimler Smart car. In India, the Tata Nano which was well designed but not manufactured to a high enough standard to become popular

David pointed out that there are many car clubs in the country where members can find like minded enthusiasts who hold rallies where members can meet other owners and perhaps buy spare parts or get technical help.

1950s- BMW ISETTA 300

30 May 2019 – Richard’s club project launch

This year, Richard will be concentrating on Baluns and Chokes, the method of operation, also when and how they might be used.  Looking at each in turn, he described their effects and benefits. He explained how and why they work, or possible not, as the case may be. Also included in the ‘mix’ was whether a voltage or current balun or choke should be considered.

Due to the complex nature of the subject, Richard’s entire slide show is reproduced on this website under the tab ‘Practical Stuff’,

16 May 2019 – James Graves, communications Pioneer

MR. JAMES GRAVES was born on the 4th August, 1833, at Chesterton, near Cambridge

A good turnout came to hear Donard, M0KRK tell of the history of under sea cables and the part James Graves played in their success. It appeared from the start that Donard knew more history of the man than expected, then he told how he was a descendant of James through his wife’s family.  As a result, he had access to a very large pile of James’ technical papers.

Donard explained that in the early days of undersea cable, little was knows about the problems about to be faced. It was a completely different story from over land cables,  A quick search will show there were many highly skilled and educated men working on the project, which in the end produced a result, overtaken only by the use of long range radio. Having said that, undersea fibre optic cables now carry gigabits of internet information around the clock

9 May 2019 – Club visit to National Radio Centre

The evening started with an introduction to the Centre from Martyn G0GMB in the reception area.  The Centre reception has been sympathetically designed to fit in with the main theme of Bletchley Park and the work done during the war.  There are HRO, AR 88 and special SOE transmitters.  Other items on display include letters to members of the VI from the RSS telling them what frequencies they need to monitor, so very much in keeping with the WW2 theme.

Tea, Coffee and biscuits were provided and served by Carmen so we were all refreshed ready for the tour.

As you work your way through the centre you are presented with different displays outlining the development of radio with images of inventors and scientist associated with radio as well as some of the equipment they would have used at that time.

After this corridor of history you have working displays on how some of the main principles of communications work.  This area enables visitors to get hands on and experience some of the methods used in radio.

As you work your way round the centre you can not help hear the sounds from the GB3RS station, which uses several different pieces of equipment from some of the main manufacturers who have donated a lot of the systems.

The volunteer operators helping out this evening were Brian, Eric and Tony, who managed to answer most of the questions from our members on the equipment the modes used and the various screens showing where signals were coming from.  There was some interest in the FT8 mode, which seemed to be receiving many signals from Europe and elsewhere.

Lots of the systems were computer controlled and everything was on large screen displays showing the grey line map of the world and locations of incoming signals.  The station was very well set-up and we all managed to get a chance to see how some of the systems worked.

The evening ended with the club’s usual round of applause and thanks to all the volunteers for their hard work and for giving up their time for our visit.

Martyn said that the Centre relies on volunteers and if anybody was interested to contact the RSGB web site for information.

A very interesting evening.

                             Text by David, G8UOD
Members arrive for the visit,                             photo by Paul, G1GSN