[TowerTalk] Fan dipole Re: Looking for a HP 80/40 Duplexer

[Jim Brown]

On 11/18/2025 12:46 PM, Jim Lux wrote:
> I'd expect substantial coupling between the fans, though.

The fans I've built use wider spacing -- 10-12 in for my 80/40 fans, 
about 8-in spacing for 15M and 10M on either side of the longest 20M 
element.

Yes, there's coupling, but not enough to affect radiation efficiency. It 
shows up as a narrowing of the SWR bandwidth on the shorter dipoles.

As I recall (from 20 years ago), the loading coils for a 80/40 dipole 
resonated in the range of 16 MHz. The SWR bandwidth of a 160/80 design 
was only about 50 kHz on 160M. I had it up around 120 ft for a year or 
two after I moved here, and ran a lot of A/B comparisons with a 100 ft 
Tee with a lot of radials. It rarely won -- even at 120 ft, a horizontal 
dipole is low in terms of the vertical pattern it produces -- so when a 
storm took it down, I rebuilt it without the loading coils.

73, Jim K9YC