TopBand: Tower matching

[km1h @ juno.com]

On Fri, 25 Jul 1997 14:04:34 -0700 (PDT) Larry Tyree <n6tr@teleport.com>
writes:
>
>First off - thanks to everyone who responded to my question about
>adding a 40 meter beam to my "magic" loaded tower.  I think regardless
>of what happens - someone will be right!  I think the one thing 
>everyone agreed on is to try it.  I will try and make some 
>measurements
>before and after to see if there is any change.
>
>The fact that the KLM elements are insulated might help.

Change might to will.


>As far as a procedure - I think empirical examples are probably the
>best way.  I would like to offer a location for examples to be stored.
>
>So, write up something on what works for you, and I will create a
>web page with all the data.  You should include things like the
>tower height - height of various antennas - gamma dimensions (height,
>conductor size, distance from tower) - capacitor values, radial
>system description and any notes you can give about the tuning
>process and performance.  

Color me somewhat old fashioned. Everyone and his dog wants to create a
web page. I really dont have the time or interest to look for them all.
Very, very few offer anything of value anyway.  You might be better off
trying to get it published in one of the print journals. ON4UN is
actively looking for new inputs for a revision of his book. IMO, that
would be an ideal place.


>
>If enough people contribute to this library - then something close
>to your situation can be used as a starting point.  
>
>Bandwidth would also be an interesting thing to note.  At my previous
>QTH - I had a flat antenna from 1.6 to 1.9 megaHertz - which would
>indicate a lot of loss - however the antenna really played!!  W2GD
>saw a similar result with a similar antenna.

An antenna can still play well with loss; it is all relative. Also if it
happens to come out at .25 wave the bandwidth will increase. It is those
highly reactive non-reasonant situations that eat up the bandwidth in the
Omega match. 

As I showed in my 1986 CQ article, the diameter AND positioning of the
gamma rod are both important along with the spacing. The worst case would
be a  #12 wire looking broadside to a 25 or 45G type of tower. 
Another poor choice is wide spacing....over 2 feet or so since the gamma
soon becomes a radiator, not a transmission line element. 
A fair compromise is .75" CATV hardline as the gamma and positioned so
that it looks at a tower leg, not broadside. 
Yes, anything will work....sometimes. The hard part is making it work
most of the time, under all wx conditions of ground resistance and with
the typical ham propensity to always change something on the tower. 

Granted, my results may not work for all but they were derived from many
hours of experimentation running field strength tests with professional
equipment in a field about 2.5  miles away. I still have most of those
notes and other data that never made it into the article. 

As K1VR and others can attest to, the system worked VERY well. Just look
at the KM1H 160M column in various contests in years past. This was all
on a 1A corner lot with the tower 50' from the road and the ground almost
all sand.  I believe that I made up for a poor location and well under
legal power by attention to details at the antenna itself.  All it takes
is effort....not an answer in a can. 

73....Carl   KM1H
>
>The 40 goes up tomorrow - we shall see what happens!
>
>73 Tree N6TR / K7RAT
>tree@contesting.com
>
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