Hi Chris, I think you know me and my approach by now :-)).....suggesting you
asked the wrong question !
Insulating the mast is possible I am sure as Mark a professional BC engineer
says..........
But a different question might be, "how to I use the tower to hold up an
effective vertical?"
Rik's tutorial is very good, and one easy way is to pull the bottom of the
vertical away from the tower structure. I think the easiest way would be to
combine a couple of ideas, both we know work from experience.
The loss to the grounded tower will probably not be that big. However the
loss is a function of the voltage on the vertical wire. Because this wire
leads from the top of the loading coil the voltage is very high (at high
powers) coupling current into the tower structure. If you reduce the
inductance in the base coil(leave sufficient to allow for weather changes)
and put the balance at the top of the mast you will greatly reduce the
voltage on the vertical wire thus reducing the current coupled into the mast
metalwork (Mike, G3XDV pioneered some of this on hs house mounted pole mast)
You have a sturdy support for the coil and to a great extent the Q or loss
factor of this coil is irrelevant. this be because the antenna current has
traversed the radion resistance before it reached the coil (well maybe not a
very technical explanation but that is the effect)
Is this better than the loop fed via a vertical wire as as a heavily
capacitance loaded vertical?? The argument goes like this.....
The tower supported vertical will have an effective height of half the tower
height because there is little capacitive loading (unless you string
horizontal wires from the top, which I believe, the "estate manager" will
veto :-))
The loop because of its high capacitance will have an effective height
almost equal to its physical height. This if the loop is about half the
height of the tower there will be little difference in the ERP between the
two systems. In fact the loop may be better, as I keep banging on about it,
the capacitive load will lead to a much lower ground loss than you will
probably see from the tower supported wire. This is relatively easy to to
check by measuring the complex impedance of the the two systems (without the
loading coil or ant tuning) I think you will findd the "R" in R+jX is much
higher for the mast and this R is 99% due to ground loss, because the
radiation resistance is minimal. Matching will not help, you need to
increase the current in the vertical section, and that can only be achieved
by reducing the ground loss..
I hope that makes sense, as it was typed rather quickly.
Best wishes
Alan
G3NYK
----- Original Message -----
From: "Chris Wilson" <dead.fets@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Saturday, June 24, 2017 5:37 PM
Subject: LF: Insulating a Versatower from ground
Hello LF'ers
Has anyone tried making insulating bushes for the tilt over hinge and
the bottom locking peg on a crank up / crank over 40 or 60 foot
Versatower? How much of a detrimental effect would the steel 6 foot
above ground, concreted in support post a couple or three inches away
from it have? Specifically I am toying with doing this to use it on LF
136kHz with my horizontal quad loop as the capacitive "top hat" to
gain as much vertical height for the radiating element as possible,
right now the mast has a long insulated line to the corner of my
horizontal quad
loop with the vertical some way from the mast, although today to
minimise sag from having the vertical some distance away I moved it
nearer the mast. By so doing I have gained maybe another 8 feet of
height. Thanks.
Thanks
--
Best regards, Chris 2E0ILY
mailto:dead.fets@gmail.com
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