[Antennaware] Trapped dipoles

Guy Olinger, K2AV olinger at bellsouth.net
Fri Nov 16 16:53:09 EST 2007

The intent was to reduce the amount of circulating current in the trap at the 
operating frequencies. However, this also changes the placement of the trap, 
the trap component values and the wire lengths involved for the same two 
frequencies. The pattern of the antenna on the higher frequency changes some 
because there is more current on the higher frequency in the outer sections.

Very tricky stuff.  Can be modeled in EZNEC for sure and probably other 

----- Original Message ----- 
From: "David Gould" <dave at g3ueg.co.uk>
To: <antennaware at contesting.com>
Sent: Friday, November 16, 2007 3:19 PM
Subject: [Antennaware] Trapped dipoles

I thought that a conventional 80m/40m trap dipole had the trap
resonant at 40m, I have now read a number of different fragments of
information that say that this is not the best approach and that the
trap should be resonant somewhere between the two desired frequencies.

I want to build a trap dipole for 40m and 30m.  There are a couple of
things I don't understand...
Does it matter what the trap resonant frequency is?
Does the trap resonant freq affect the "inner" length of the dipole
from feed point to the trap to give resonance on the higher
frequency  ( Trimming the outer length to the lower frequency would
be straightforward)

Any help or links to some detailed description would be appreciated.

Dave, G3UEG

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