[Antennas] 80 meter delta loop

[Terry Conboy]

At 02:49 PM 2004-04-06, VE7SQ wrote:
>A single delta loop impedance is approx. 100 ohms.

Just so we're talking about the same configuration, I think W4TEY was 
referring to a triangular horizontal plane loop (aka "Loop Skywire").

The 100 ohm impedance is a good value to assume for average 
installations.  When I gave the 70-80 ohm number it was for my local ground 
(0.03, 15) at 25-30 feet high.

With average ground (0.005, 13) it is a bit higher: at 25 feet it is about 
85 ohms, rising to 92 ohms at 30 feet and 100 ohms at 35 feet. At 60 feet, 
it is about 145 ohms.

>One method is to cut a length of 72 or 75 ohm coax 1/4 wavelength long to 
>the feedpoint.

This is a great approach.  For an antenna feed impedance anywhere between 
87 ohms and 146 ohms, the 50 ohm SWR after a 1/4 wavelength of 75 ohm line 
is only 1.3:1, which is pretty good.

>I have used a Pawsey balun for matching also. The Pawsey balun is a quarter
>wavelength long too and can be made adjustable. You can get that information
>from the ARRL antenna handbook.

I'm hadn't heard of the Pawsey balun before and I couldn't find it by that 
name in any of the recent ARRL Antenna Books, but from 
http://www.cqham.ru/rw6at/2003/pawsey.gif it appears that it is a parallel 
stub balun.  Isn't it normally 1:1?  I suppose it could be made from 75 ohm 
or other impedance line to provide an impedance step up or down.  How do 
you make it adjustable?

Thanks & 73,
Terry


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