[TowerTalk] 80 Meter trap design needed

[Jim Brown]

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