> 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@contesting.com
> [mailto:towertalk-bounces@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.
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