On Mon, 23 Mar 1998 21:07:48 +0000 Andrew Williamson
SNIP
>'Loud' maybe, but not loud enough Carl ;-) I have no idea of the
>ground
>conductivity. It is heavy soil, I suppose half peat and half clay
>with
>a solid rock base about three to four feet below the surface. The
>concrete base of the tower is actually about a foot into the rock. It
>wasn't fun digging THAT out, even with a mechanical digger!!
I am not familiar with peat...except in Sherlock Holmes tales! Isnt that
just a mass of organic growth? In the US, the good topsoil and clay base
found thruout much of our Southern states has a conductivity in the 2 to
5 mS/m range. The rock 3' down does not help.
>
>I knew there would be a problem somewhere. BW isn't a major issue,
>provided it covers at least 1.81-1.87 which is where all the
>contesters
>operate. When you say the BW should be excellent, I'm assuming you
>mean
>more than 60Khz.
A 2:1 BW of 80-100kHz should be attainable without a matching section in
a conventional 1/4 wave vertical over a good, efficient ground system.
The difficulty arises with shunt feeds in the matching system when high
Q vacuum variables are used....and the more the deviation from 90 degrees
the more the effect.
If this is the case, I'd be more than happy to trade
>some BW for an efficient, easy to match system, if such a thing exists
>for this type of structure.
Please let us all know the responses. My comments are based upon my own
experiences with a shunt fed tower that was resonant around 1400 kHz.
With 16 radials on the ground the BW was about 150kHz, after 25,000' of
wire was installed plus a mesh the BW dropped to 20kHz. All intermediate
increments showed a steadily decreasing BW.
Here is an idea....possibly crazy...but Ive been accused of that already.
How about multiple parallel gamma rods...maybe spaced every 1' at the
base and tapering in along with the tower?
GL !! Carl KM1H
>
>Thanks for your help.
>
>Vy 73,
>
>Andrew Williamson GI0NWG / AC6WI
>Homepage = http://www.gi0nwg.demon.co.uk/
>
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>FAQ on WWW: http://www.contesting.com/topband.html
>Submissions: topband@contesting.com
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>Problems: owner-topband@contesting.com
>
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