Back in the attic antenna days, I used a trap 160/80 at the house. Was
running CW & RTTY then and kept frying coax type traps. As they heated
up the SWR would move around and you could see it on key down. The
failures of those coax types were impressive! Lucky I did not burn the
house down, when I think of it in retrospect.
Eventually went to a 1/4" copper tubing + Russian fixed vac cap
construction type - and that was the end of those trap failures. The
trap was a monster, but it was low loss, high Q and indestructible.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 10/23/21 8:32 PM, WW3S wrote:
my recent 80M trap experience.....my previous 160m ant was an inverted
L suspended off a hazer on my Rohn 25 tower.....when higher winds or
storms I cranked the hazer down, so was out of business on
160M......been looking for an alternative, and one of my other
antennas is a Hygain Hytower.....most of what I heard about the 160M
kit for the Hytower wasnt good......I just so happened to have a W2AU
80M trap with the ability to mount via tubing......so.....bright idea,
I would replace the stinger on my Hytower with different size tubing,
allowing me to mount the trap on top of the hytower, and attach a
loading wire to it.....I had most of the tubing I needed, ordered what
few pieces I needed....I built the new stinger to the length of the
old one (probably my first mistake), attached the trap, and about 47
ft of wire (per the instructions from Unadilla for a wire
antenna)......tilted the tower back up, swr was a little higher than
before on 80M, but was less than 1.5:1 at 1820 so I left
it.......worked a few stations on 160, worked a few on 80, everything
seemed good......until........until I tried to work S9OK on
160M.....with the amp.....at about 1400 watts.....calling for about an
hour and them something went south in a hurry.....swr all over the
place on 160 and 80.....I havent had the chance to tilt it back over
but I suspect the trap overheated.......another bright idea that wasnt
so bright after all.....
------ Original Message ------
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Sent: 10/23/2021 2:54:20 PM
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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