Traps and advertising claims

Dennis Schaefer
Sun, 16 Feb 1997 20:43:21 -0600

The C-3 probably has been kicked around enough.   It's a competitive
antenna for its size and weight.  However, the recent discussion brings to
mind the way traps are treated by antenna manufacturers who do not use them
such as Force 12 and  Sommer.  I quote from the catalog of a trap-free
manufacturer:   (And I won't name them to keep them from getting defensive)

"if the antenna has a fine pattern, it has the potential for gain, but does
not necessarily have gain, as any potential gain can be lost in traps,
matching circuits, phasing systems and other conductors in the antenna.  If
the antenna does have coils (found in traps and also used for loading
purposes), it might well have zero, or even negative gain.  Models of
coil-loaded 2 and 3 element beams (e.g. 2 element 40 mtr and 3 element
tribanders on 20 meters) confirm that the actual (potential) gain is less
than 2dB with great coils (Q=100) and less than 0.5 dB with average coils
(Q=25 to 50).  The "beam" is actually a directional dipole."

The implication is that actual common  brands of  "tribanders" have been
tested and found to have almost no gain!     Of course, traps are not
trouble free, and water, dirt daubers, lightning, and high power can cause
problems.  However, we are talking about basic performance here, and trap
antennas seem to be capable of meaningful gain. 

Has anyone studied the performance of standard (Hy-Gain, Mosley) traps  in
depth, similar to Tony's analysis of KLM trap losses?

My experience with traps is "anecdotal" as opposed to scientific.

1.  I am temporarily using an A-3 until the weather gets better and I can
put up a KT-34A.   However, the A-3 certainly seems to have more than 2 db
gain over a dipole.  Must have REALLY GREAT coils, according to the ad
quoted above!!

2.  I operated as KA2DX in Japan in the early 70's.  Some of the best
stateside 20 meter signals I  heard came from the TH6DXX.  (And the guys
couldn't have been using too much power, or those "inefficient " traps
would have been toast).  

3.  I once replaced a 203BA (3 el 20 M monobander/16 ft boom) with a Mosley
PRO-57 (3 el on 20, 24 foot boom).    The Mosley was noticeably better, and
the  50% increase in boom length  more than overcame the trap losses.
There was definitely a new "layer" of workable DX.  The original PRO-57 was
actually a pretty good antenna on 20-15-10.  The mod to also make it work
on 12 and 17 seemed to affect performance on 20-15-10,  so I sold it.

Monobanders are best, and probably interlaced full-size elements are next
best, but  trap antennas are  effective compromises.  Companies who
relegate them to the "dummy load" category in advertising lose credibility.

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