[TowerTalk] 80 Meter trap design needed

[Jeff Blaine]

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 at audiosystemsgroup.com>
> To: towertalk at 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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>>
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