Interesting Items urgently required  for Newsletter

This year seems to be flying by so quickly. I wonder what everyone has achieved in the last year, I wonder whether everyone has achieved all the personal goals that they set themselves, I wonder whether everyone feels that the ye& has flown by as I do. I wonder what interesting contacts anybody has made in the last year..

Food for thought..

Perhaps the answers to these questions would make inter-esting reading to your fellow news-letter readers. So come on, put pen to paper and help me to write these newsletters. We are a CLUB and without you we would not exist as a club so the newsletter should be a CLUB effort.

I think the newsletter should or could carry a technical article every month. This could be on anything connected with Amateur Radio, I am sure that any articles could only  be of benefit to us. (and it would take up some space HIHI) Overleaf you will find a short description of 'Tuned Traps

Also the newsletter could carry a simple one line 'Quote of the Month' I shall star the ball rolling on this one.

Any ideas for the above on a piece of paper please to the editor.

Some good news now. Members will be pleased to hear that Brian Barrett MlDBM is making a good recovery following major heart surgery Brian even felt well enough to attend a club meeting on 27/09/2002. He hopes to be on the air again soon.

We still need volunteers to help with the refurbishment of the clubs headquarters.

Barry M3BIW and Steve M5PDL are trying to get a Slow Scan TV net off the ground. Anybody who may be interested in this mode can contact any of the 2 members listed above for further details.

Are any of the clubs members prepared to give a talk to their fellow members. The duration of the Talk need only last 15-20 minutes if needs be, and the subject doesn'1 have to be about radio, You pick the subject and the date and the 'Floor is Yours'

If you feel that you can't stand before a 'crowd' then perhaps you can put pen to paper and write an article for the newsletter

In last months newsletter I published a list of Committee Members. It has been brought to my attention that I left a committee members name off the list. I was not made aware at the AGM that the following member was in fact a committee member Terry Lishman GOWVD. . Sorry Terry.. .ed.

Tuned Traps

'You either Love em. or Hate them'

You either love them or you hate them! Tuned traps are the mainstay of many antenna Systems, both commercially and home-brew. Their task is to isolate a section of an antenna on one discrete frequency. In this respect they act as an insulator. But, it is important to realise their limitations and shortcomings. Not because there is any obvious alternative, but because they can limit the ultimate performance of your antenna.

An HF tuned parallel trap has the function of passing all frequencies other than the one to which it is tuned. At the resonant frequency it acts as a block with the remainder of the antenna beyond it having very little part to play. However, it is not a perfect isolator and just how effective it is depends on it's Q factor. Some energy will be absorbed into the trap and some will leak through. This represents a loss, and therefore a reduction in antenna efficiency. The RF leakage can also be responsible for a small increase in VSWR. The trap will also have some loading effect, situated as it is at the end of the active section of the antenna; and so dimensions will be slightly shorter than for a mono band antenna. The higher the Q the less will be the losses. Unfortunately a high Q trap does not solve the problems.

I have highlighted how a tuned circuit passes energy either side of it's resonant frequency.

This is one of the reasons for antenna bandwidths becoming narrower when traps are used (quite apart from the loading effect which reduces the antenna size, particularly on the lowest band the antenna operates on). As the operating frequency moves away from the precise resonant frequency of the trap, energy begins to pass through it and the antenna rapidly becomes longer and therefore non-resonant. As a result the VSWR rises.

As I said at the outset, there is no obvious alternative. Designs such as the G5RV and the Windom avoid the use of traps, but are locked into the ability to only cover certain bands. The beauty of traps is that they can be used to produce an antenna that is able to operate on several frequencies at random points throughout the spectrum. Don't lose too much sleep over the problem, but appreciate the shortcomings.

A trap antenna will have a narrower bandwidth and will not be as efficient as it's full-size equivalent. A single band dipole is a very efficient antenna, but not much good when the band closes and you have no other band to operate on.

Please let me know what you think of your new look news letter Steve M5PDL