[TowerTalk] Help: how to feed a loaded delta loop?

Robert G. Strickland rcrgs at verizon.net
Mon Jul 28 21:16:18 EDT 2008

Hello, all...

Using EZNEC, I have designed a 40M reduced size delta loop that uses 
450ohm ladder line in the lower corners to give the required inductance 
for the reduced size I need at my QTH. Now the question: EZNEC indicates 
that the feed impedance for this loaded loop runs   from around 35ohms 
at a lower corner to about 60ohms at the apex. EZNEC also "suggests" 
that the radiation pattern is fairly constant for just about any feed 
point along the sloping vertical section. I know that full size loops 
are fed 1/4 wave down from the vertical. However, with this reduced 
loop, 1/4 wave from the apex wraps around the lower corner and starts 
out along the horizontal lower section. Where should I feed this thing?

A second question arises as to the feed line. With my previous full size 
delta loop, I used 1/4 wave 72ohm coax to bring the impedance to around 
50ohms at the shack end of the feed line. This antenna performed well. I 
worked Heard Isl. barefoot with one call on 40M from WNY. Also, on the 
full size loop, I put a ferrite choke balun on the coax at the feed 
point. In retrospect, I don't think that such a choke is needed and may 
even be contraindicated. After all, the delta loop is not a symmetrical 
antenna when fed 1/4 wave from the apex. Any thoughts on this point?

Thanks much for any and all comments.

Robert G. Strickland PhD ABPH - KE2WY
rcrgs at verizon.net.usa
Syracuse, New York, USA

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