[Elecraft] wire antennas

[Ron D'Eau Claire]

I use a traditional wide-range balanced tuner - the same circuit Cebik shows
and that has been a Hamshack staple item among some of us since Marconi was
around. Center link, split stator variable, and feeders tapped onto the
coil. 

With that tuner feedline length has never been an issue at all. It matches
easily values from a few ohms up to several thousand ohms: the highest
impedance one might expect with typical antenna geometries. It uses a large
coil with heavy wire to avoid ohmic losses at the low impedance end and
wide-spaced transmitting cap to handle the very large RF voltages present
feeding high impedance loads. 

It's not automatic, so it's not fast, but I can change bands in about 15
seconds. And it's flexible, handling unbalanced loads like an end fed wire
or coax line with equal ease. 

My normal feedline is high-efficiency open wire line.  My open wire line is
made of #14 electrical wire separated by high-quality ceramic insulators at
long intervals to minimize dielectric and ohmic losses. 

My antenna of choice has always been the doublet, since I've not had the
space for a rhombic or other traveling wave type or the room for a tower and
beam. As long as the doublet is at least 1/4 wavelength long, end to end,
it's  virtually as effective as a half wave. So a 66 foot doublet does a
very good job on 80 and a 130 foot doublet does a good job on 160. The big
issue on the lower bands is usually height, especially enough height for
good low angle radiation from a horizontal antenna. That requires a height
of at least 3/8 wave and 1/2 wave is better. On 160 meters it needs to be
close to 100 feet up: 130 feet would be ideal <G>. I count myself lucky to
get the wire 50 feet up. That provides low angles for DX on 40 meters and
up. On 80 or 160 it's an omni-directional NVIS or "short skip" antenna
providing excellent coverage out to about 1,000 miles or so on 80; a little
less, typically, on 160. 

Where the wire is well over 1/2 wave long, it shows significant gain as the
pattern breaks up into many lobes. In spite of the antenna patterns one
finds in books, a real world antenna does not have zero radiation in any
direction. It's a matter of having lobes that produce a superior signal in
various directions. I've never noticed any deleterious effects from the
lobes and long ago quit thinking much about trying to align the antenna for
specific coverage.
 
Ron AC7AC



-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David Cutter
Sent: Tuesday, February 20, 2007 4:14 PM
To: Mike Morrow; elecraft at mailman.qth.net
Subject: Re: [Elecraft] wire antennas


I always advise using a non-resonant length for a multi-band doublet with 
tuner combination.  There's a magic figure: multiples of 44ft, 88ft... that 
Cebik came up with which is a good compromise with impedance matching, ie 
not horrendously high or low X and R.  I notice no-one has mentioned the 
G5RV and its derivatives, yet.

David
G3UNA