Delta loop

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Joined: Sun May 13, 2012 4:21 pm

Delta loop

Post by wb9otx » Wed Jan 27, 2016 6:44 pm

I put up a full size 17 meter delta loop with coax and a 4 to 1 balun. It had a very high SWR, un-usable to say the least. I took out the balun and feed it direct with coax and after adding a few inches to it, it is now 1 to 1 at center band. Everything I read says use a 4 to 1 balun, why does it work without it??

Posts: 45
Joined: Sun May 31, 2009 2:40 am
Location: Melrose Fl.

Re: Delta loop

Post by KB3LMV » Thu Jan 28, 2016 6:37 pm

Hello Jack
According to John D Heys G3BDQ Practical Wire Antennas,Delta loop formula is 1005/Freq = length in ft.Feed point impedance is about 75 ohms for an equilateral delta loop.I,d use a 1 to 1 Balun and 75 ohm Coax feed line to your radio.75/4 = 18.75 ohms Not An Acceptable match in my eyes,keep the fire bottle handy.
Hope my Info is helpful and good luck on 17.
73 4 now

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Joined: Sat Mar 24, 2012 5:43 pm

Re: Delta loop

Post by ku3x » Sun Feb 07, 2016 10:18 pm

The feed point impedance changes as you change the delta loops height above ground. It also changes as you move the feed point from the bottom to different points around the antenna. If you make a
true delta loop with the apex up, the 4 to 1 balun will usually work fine if it's placed at the apex.

I have a full size 80 meter delta loop and the base of that antenna is about 10 feet above the ground. It is fed in the bottom corner and the feed point impedance is 142 ohms. My first 80 meter delta loop was 80% of a full size with the use of four coils. The feed point impedance was 95 ohms fed in the bottom corner.

Barry, KU3X

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