[TowerTalk] 80 Meter trap design needed

[Mike Ryan]

Jim et al, I have been using the HyPower Antenna 160/80 antenna here over
the last 3-4 years.  They have two models one a bit longer than the other. I
use the longer model here. These work well on 80m but as Jim points out they
are going to be narrow on 160m. Another facet that took some adjusting to is
that fact that the ends of the antenna get EXTREMELY hot, no doubt a result
of the transmit time on FT8.  Even when both bands are adjusted to a very
acceptable SWR, the 160m or long portion of the antenna will go so hot that
it melts your typical 'dog bone' insulator.  It won't matter if this
insulator is glass, plastic, or ceramic, it will BREAK and the antenna will
fall to earth...trust me.  What I found that does work are very long and
heavy (14" long weighing close to a pound I would say) ceramic insulators
with metallic inserts pressed into the ends where the antenna's wire passes
through (one side) and your dacron line or parachute cord goes through the
other side. These have held up well.  Nothing else I have tried has ever
worked.  The coils on this antenna I also coat with JB Weld clear epoxy so
that the coating from the 'factory' holds up better under uv, etc.
Otherwise, the gauge of wire used (#12 solid) is robust and the coils appear
to be made well. I like the antenna.  Your results may vary but be wary of
cheap insulators when using one if running high power.  -Mike, K4CVL

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim
Brown
Sent: Saturday, October 23, 2021 2:54 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] 80 Meter trap design needed

On 10/23/2021 4:56 AM, Mark - N5OT wrote:
> I hope to make a trap vertical that works on 80 and 160.

First question is, why a trap? If it's not height, consider a fan.

Second, there's a design for 2-band 2nd harmonic dipoles where there's a 
loading coil (NOT a trap) near what would be the quarter-wave point of 
the lower frequency band, with a relatively short wire beyond it. That 
design has relatively narrow SWR bandwidth on the lower frequency band, 
but bandwidth comparable to dipole on the higher band.

This design works quite well, and there have been several successful 
commercial implementations of it. Hypower Antenna Company (tiny ad in 
QST) sells them, and may sell the loading coils separately. I measured 
their coils for the 160/80 and 80/40 designs many years ago, and can 
probably find the data. But it's a fairly easy design to do in NEC, and 
I recently did one for a 40/20 dipole made from Al tubing for use on CQP 
county expeditions.

73, Jim K9YC
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