The past couple of days I've been reviewing literature on trap dipoles.
My goal is to build a Field Day dipole for 40, 20, 15, and 10 meters (the
club already has 80m covered). For simplicity of operation, I want to avoid
an outboard tuner. So I'm considering a balun fed dipole that can be
trimmed up at the band edges with a rig's built in tuner if necessary. I
also want to avoid the patterns that occur on the upper bands with a
longer wire (I have looked over W4RNL's 44 foot multibander with interest,
but the high impedance on 15m requires a ladderline feed and a tuner, so
I've discounted it for this project).

So, I'm left with two practical alternatives, a fan or a trap dipole.
From reading this group's archives and various web pages, I've come to the
conclusion that while the fan dipole is simple to construct it is
susceptible to element interaction and may require additional support or
care in element spacing and antenna erection. These points seem to weigh
against it for a quick and nearly fool-proof antenna for Field
Day/event/emergency use.

That leaves me considering a trapped dipole. In this category are traps
using an inductor and capacitor and those made from coaxial cable. W8JI
has documented just how poorly these traps will probably perform compared
to those made of discrete components. However, given their (apparently,
as I haven't tried to build any yet) low cost they may perform well enough.

More research has uncovered that suitable capacitors and inductors are
hard, if not impossible, to find and when procured the parts may cost as
much (more?) as the Reyco traps offered by Unadilla. Perhaps decent
performance does have its price and the price for three pairs Unadilla
traps is reasonable for the simplicity I desire.

I guess this is a long and rambling post to get to the point that the trap
has become sort of a historical device in modern amateur radio antenna
implementations except for commercial yagis. For the record, at my home
QTH I use a center fed Zepp style antenna with a tuner, so I'm not averse
to that concept, I just want to avoid it with this special project.

Despite the lack of literature, are there some trap projects that are easy
to build, but perform better than coaxial traps? I must admit that I'm
not to good at scratch building things as I'm better at fixing stuff or
following a pattern than spending a long time experimenting.

I know this is long, but I wanted to share my thoughts to show the track
of my thinking on this.

73, de Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."