[UK-CONTEST] More about DX loops

[Adrian Rees (M1LCR)]

Hi Callum and list
I made the Tee Piece of the 40M Delta Loop we used at WPX this year out of a
Plastic Piping Tee Piece. The sort of thing that is 1 inch in diameter....

First of all I got hold of two Bolts, about 2 Inches long, drilled a hole
through two 2p Pieces (I know I know, defacing the Queens Currency!) and put
the bolt through each of the 2p pieces, pulling up tight on the nut. I then
threaded the Quarter Wave line of 75 Ohm Coax, through the vertical of the
Tee, and soldered the braid to one 2p piece, the centre to the other.

Using Araldite, the 2p piece was glued in position, (well first of all
jammed in position, then Araldited to stop it from moving.) Once one side
was done, I did the other. I then packed the remaining space with some
Plastic Padding, leaving about 1 1/4 " of the bolts either side protruding.
Using a pair of wing nuts and washers, I attached the aerial elements.

The 75 OHm Coax I used was from a length of of old 75 Ohm Twinax (Ex
Computer networking stuff, same size as RG 58, probably RG 59) that I had.

Wire wise (aerial element) I use the stuff electricians use for ceiling
lights. 7 Cores, quite thick and very strong. You can buy it in 100M Rolls
for about ?7.50 (inc VAT) from your local Electrical Supplies place. (They
have gotten to know me in the Chester Branch, and keep the strange colored
stuff for me, slightly cheaper, and a Purple Aerial !)

It will take a hell of strain, for example we used it for a Top Band Dipole,
at 60 Feet, using RG213 to feed it with, and got it flat on top, without
sagging.

As long as you have the space, Callum, I'd use that stuff, and pull the
Triangle shape out by the legs. Support the Feeder Coax with an additional
rope, via the Halyard, that way you'll only have a relatively short run to
support, and it won't weigh too heavy on the aerial elemnts.

Adrian (M1LCR)

-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com]On Behalf Of Callum
Sent: 04 April 2005 17:59
To: uk-contest at contesting.com
Subject: [UK-CONTEST] More about DX loops


Thanks to Alan and John who both mentioned similar aspects of loops for DX -
also to Adrian who brought the topic up..

In my mind, I have a loop for 80 meters, slung off the 100 foot trailer
tower at a club field day event. I was going to use a 4:1 balun, however
perhaps I could get away with a few turns of coax? 4:1 might be too steep.

My dilemma is that if I feed this 1/4 wave down one of the legs, the weight
of the balun / coax / feedline etc will pull the delta loop into an odd
shape. 1/4 wave "down" is just about a third up from the bottom (I'll work
it out - this is just for example!) - I wonder the best way of supporting
this, or perhaps I use a heavier gauge wire than I normally do and just pull
it tight to take the "bend" out? I don't want to snap the balun etc. I built
a 40 meter vertical delta loop for CQWW last year and fed it like this, but
I supported the weight by managing to take the coax off at 90 degrees to an
upstairs room so there wasn't mush real weight on the thing.

Any ideas on the engineering side, how I might do this as it's really
nagging me?

Callum.


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