Center-fed doublets of various lengths have been with us for 50 years or
more.
I've only been licensed that long, so I won't guess before that.
When horizontal and having a reduced space requirement, I have usually used
between 7m and 7.5m per side, which is basically the 44 ft. doublet L.B.
Cebik describes.
In this case, I chose a shorter length for a specific reason.
The idea of turning the doublet vertical was of course in the interest of
saving space.
However it has other advantages, especially on the low bands.
On the high bands, I would always prefer a horizontal dipole if mounted high
enough because it is usually quieter and I can rotate it to improve strength
in one direction, or reduce QRM in another.
On the low bands, a vertical is often the only choice we have, due to space
available.
I chose the 6m per side length (that's about 19' 8" per side) because that
is the maximum length you can make the sides before the radiated lobe on 10m
begins to break up into several smaller vertical lobes. Today I can also
say "because it will fit on one of our Spiderbeam 12m telescoping fiberglass
poles" - but the truth is, I was already using this antenna several years
before Spiderbeam was founded.
Trying to cover 8 bands with a single antenna is always a compromise.
When I have a beam for the upper bands, I generally make my vertical dipole
50% longer (2x 9m). This fits nicely on the Spiderbeam 18m telescoping
fiberglass poles and has a much stronger signal on 80m than when using the
smaller version. However it is not very good on 10, 12, and even 15m.
Again, the important thing (IMO) is to avoid any length that is a resonant
half wavelength on any particular ham band.
Also, the ARRL Handbook or Antenna Handbook and most other books recommend
to NEVER use a dipole on half its resonant frequency. The reason of course
is the extremely low impedance it will have on that band. This does not
mean that the antenna won't work well. It only means you will have
difficulty matching it. And the second reason is, when running coax, you
will have a lot of loss in the coax. This is not so important when running
openwire.
What the handbook does not tell you that, if you can find a way to
efficiently match it, a half-size antenna or even smaller, can still be a
very effective antenna. It is always better to go with a larger antenna but
sometimes that won't work.
The symmetrical coupler you referred to, using alligator clips for changing
bands, generally has no problem matching these low impedances- or high
impedance, for that matter. However most auto tuners won't manage.
Somehow, building manual link coupled tuners with alligator clips is a lost
art. Too bad. They were very effective and relatively simple to build.
They were only complex if you wanted to switch bands with a switch.
In 1979 I was on a DX-Pedition to a mountain top in Andorra.
I ran an openwire fed lazy loop (80m horizontal loop).
I matched it with just such an antenna tuner (alligator clips, link
coupling, etc.).
It is the wooden box sitting on top of the Ten-Tec Omni in the picture on
this page:
http://www.dj0ip.de/my-expeditions/andorra-1979/
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Al Gulseth
Sent: Monday, March 02, 2015 5:54 PM
To: tentec@contesting.com
Cc: Jim Allen
Subject: Re: [TenTec] Hot Dang - Rick is a Best Link of the Week on
DX-zone.com
For < 100W I'd say perhaps a z-match or homebrew link coupled tuner. (The
link coupled ones can be fairly simple if you don't mind moving coil taps
etc. to change bands.) That being said, I'll let the antenna wizards weigh
in.
BTW - this antenna appears to be an offshoot of the 44' +/- doublet by L. B.
Cebik W4RNL (SK) et al. (Does spiraling the wire and/or the fiberglass pole
etc. affect the velocity factor and account for the length difference?)
TNX/73, Al
On Mon March 2 2015 8:37:06 am Jim Allen wrote:
> What "matchbox" is the right kind, for 100 watt or less use?
>
> 73 de W6OGC. Jim Allen
>
> Sent from my iPad
>
> >> On Sun,3/1/2015 11:54 PM, Rick - DJ0IP / NJ0IP wrote:
> >> In all honesty I believe this antenna is one of the best kept
> >> secrets in ham radio.
> >> Takes up nearly zero space and works 80 thru 10m if you have the
> >> right kind of matchbox.
> >
> > _______________________________________________
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> > TenTec@contesting.com
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>
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