[TowerTalk] Folded dipole

[Joe Subich, W4TV]

> The folded dipole *might* get the impedance to a better value 
> for the tuner.  To a first order, a folded dipole has 4x the 
> feedpoint impedance of the straight dipole.

But only on a single band (or at best 80/30, 40/15 meters).  
Unlike the "normal" dipole/doublet the folded dipole presents 
a zero Ohm (very low impedance) load to the feedline at all 
2n harmonics.  

As long as one is looking for strictly a single band antenna, 
a wide spaced folded dipole has some interesting advantages 
but multiple band use with a tuner is not one of them.  Note, 
I am not talking about the inefficient T2FD (loaded folded 
dipole) designs. 

73, 

   ... Joe, W4TV 
 


> -----Original Message-----
> From: towertalk-bounces at contesting.com 
> [mailto:towertalk-bounces at contesting.com] On Behalf Of jimlux
> Sent: Tuesday, August 25, 2009 9:54 AM
> To: Tom Osborne
> Cc: Towertalk
> Subject: Re: [TowerTalk] Folded dipole
> 
> 
> Tom Osborne wrote:
> > Hi All
> > 
> > Looking to put up another 40 meter antenna.  Need a NVIS antenna for
> > close-in work.
> > 
> > Is there any reason to put up a folded dipole instead of a 
> > tuned-feeder
> > dipole?
> > 
> > I think when this antenna was popular, it was touted to have more 
> > bandwidth
> > than a dipole.  But, if you have to use an antenna tuner to 
> tune it anyway, 
> > there doesn't seem to be any advantage over a regular 
> antenna, bandwidth 
> > wise.  73
> 
> 
> The folded dipole *might* get the impedance to a better value for the 
> tuner.  To a first order, a folded dipole has 4x the 
> feedpoint impedance 
> of the straight dipole.
> 
> If you were talking about the terminated folded dipole (e.g. 
> the things 
> from B&W, among others), then the loss in the antenna makes it a 
> broadband unit without a tuner.
> 
> A lot of practical systems use the lossy dipole approach so 
> they don't 
> have to use a tuner, and just make up for the loss with a 
> bigger power 
> amp.  If you have a wide band to tune over (e.g. supporting emergency 
> comm with a NVIS antenna, and you might have to tune anywhere) this 
> isn't a bad approach.