[UK-CONTEST] More about DX loops

[Clive GM3POI]

Callum,
The best way to feed a loop that is also light is to use a quarter wave of 
75 ohm ribbon. That will transform an expected Z of 110-120 ohms down to 50 
ohms where you can introduce a 1:1 balun. Alternatively you could also 
corner feed it and not bother with a quarter wave down one side. From 
modelling you would see it is still very much vertical polarization, I did 
this on my old 160 delta loop that worked rather well.
73 Clive GM3POI
----- Original Message ----- 
From: "Callum" <callum at mccormick.uk.com>
To: <uk-contest at contesting.com>
Sent: Monday, April 04, 2005 4:58 PM
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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