[TenTec] OT Kind of. ?? about wide band antennas

[Rick - NJ0IP / DJ0IP]

To cover the entire 75/80m band with a low SWR, the wire, or rather tube
would need to be about 3 ft. in diameter.
The proven way to do this in a practical sense is to use 3 or more wires.
The latest ARRL book on Wire Antennas suggests a 4-wire cage dipole, with
the wires spread about 2 feet or maybe 3 (I'm recalling from memory).  It
has low SWR across the band.

I have also used the antenna Jerry described at two different locations.
That was in Europe where we only have 300 KHz on 80m.
I called it the Fan dipole but that was just my own name for it.
It had under about 1.8 to 1 across our band.
It was also significantly shorter than a single wire dipole.
This was 20 years ago but as I recall, I had the ends spread about 10 ft.

An even better solution, if you have the [vertical] room is to user a full
wavelength of wire on each side, and loop the ends back to the feedpoint and
connect them.
Both ends of the wire tie together to the balun, on each side.
You pull the top wire tight, and let the bottom wire sag, almost into a half
circle.
Of course this shortens it substantially.
This one covers the whole band too.

This antenna was described in CQDL about 8 years ago by a neighbor of my
mother-in-law.
So I dropped in on him for a demonstration.
It works!
I just never had 3 elevate masts to accommodate the necessary height.

73
Rick

-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Richards
Sent: Thursday, February 03, 2011 6:06 PM
To: geraldj at weather.net; Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] OT Kind of. ?? about wide band antennas

My research into this, including cage dipoles, suggests one may realize 
little practical tangible effect on SWR bandwidth when replacing a heavy 
wire antenna element with a small aluminum tube  (where "small" = 1-2 
inches in diameter.)    Theoretically (I believe)  it would have more 
impact on higher frequencies a the size of the element increases 
relative to wavelength.

There is some discussion of this in the ARRL Antenna Handbook.  See page 
9-4 and 2-3, et. seq.   where it discussed the impact of larger diameter 
elements on impedance.

Hope that points in a useful direction.

Happy Trails.
=======================  Richards / K8JHR  =========================

On 2/3/2011 5:30 PM, Dr. Gerald N. Johnson wrote:
> That slow change of the resistive component and rapid change of the
> reactive component is much more prominent if you look at the parallel
> admittance than the series impedance.
>
> 73
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