[Top] [All Lists]

Re: [TowerTalk] Combined Dipoles

To: Tower Talk List <>
Subject: Re: [TowerTalk] Combined Dipoles
From: Paul Kelley N1BUG <>
Date: Wed, 16 Apr 2008 14:08:20 -0400
List-post: <">>
I have used various configurations like this on and off for 25 years 
and I agree with everything Jim says.

One year at our club Field Day operation we made one with wires for 
160/80/40/20/15/10. Theoretically the 40 would have taken care of 15 
also, but we were having fun adding wires! :) I think we used 1200 
feet of rope tying off the ends. That beast was heavy. We needed two 
or three people on the rope used to hoist the thing up... with one 
person we had the antenna and an operator dangling on opposite ends 
of a rope! I think there's a picture of that in existence somewhere...

Paul N1BUG

Jim Brown wrote:
> Some things I've learned:
> 1) The longest dipole of the fan will exhibit its "normal" SWR 
> bandwidth. Shorter dipoles in the fan will have their SWR 
> bandwidth reduced by about half. With a good tuner (I use TenTec 
> 229s and 238s) I can run these fans over the bottom 3/4 of 80M, 
> all of 40, 20, and 15, and the lower half of 10M. I could probably 
> use the 20/15/10 at the top of 10 too, but I've never tried to 
> operate above 28.55.  
> 2) A 3-wire 20/15/10 fan will look like 50 ohms even if it is 
> quite high. Ordinary dipoles will be pretty close to 75 ohms if 
> they're quite high. 
> 3) Some references say that one dipole will be detuned by some 
> percentage by the others. I've never been able to measure that. 
> 4) I would NOT try to put dipoles in a fan that are "in between 
> harmonics" of others in the fan. That is, I would not put 30M in a 
> fan with 40, because it is more likely to interact with the other 
> dipoles. On the other hand, my 80/40 fans load quite nicely on 
> 30M, and they play very well. They also load and work well on 17M 
> and 12M! 
> 5) If you have limited space, don't rule out loaded dipoles like 
> those sold by HyPower Antenna Company. I've used them a lot, and 
> they work quite well. NEC modeling shows that their efficiency is 
> only a fractional dB below a full size dipole. The compromise is 
> reduced SWR bandwidth, but you can still use them effectively over 
> an entire band at full power with a good tuner. 
> 73,
> Jim Brown K9YC

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>