Shunt Feed Tower for 80 meters 160 meters
[mailto:firstname.lastname@example.org] On Behalf Of Jim Smith
Sent: Monday, February 02, 2004 4:39 AM
Subject: [TowerTalk] Inverted L Questions
I'm in the process of putting up an inverted L for 160. In the back
corner of the lot I'm going to put up 30 ft of very skinny tower. The
cross bracing looks like Rohn 25 but the face is only 6.5" The legs are
solid. The whole thing is made of aluminum. I have 50 ft of the stuff
but 50 ft would put it 20 ft higher than the HV line which runs down the
other side of the back lane.
The tower will be insulated from ground and fed at the base. To the top
of the tower will be fastened a length of stranded Cu antenna wire which
will run along the lot boundary to the top of a 30 ft mast (could dangle
down a bit if I need the extra length) at the front corner of the lot,
about 120 ft away.
There will be a ground plate (we use plates here, not rods) buried at
the base of the tower to which the coax shield will be connected.
The tower will be self supported with maybe a couple of guys such that,
if anything bad happens to it, it will fall inside my property.
The 40 and 80 dipoles will be moved to this tower from the 16 ft mast to
which they are currently attached.
I have 2 questions
1. How to fasten the stranded wire to the top of the Al tower.
I was thinking of just putting a stainless hose clamp around one of
the tower legs, putting the wire through it and tightening.
However, I think the wire would fatigue very quickly and break.
Easy enough to get the tower down to fix it but would prefer not to
have to do this every couple of months.
Another thought was to wrap, say, 10 turns of the antenna wire
around the tower leg and cover the bottom 5 or so turns with the
hose clamp. These are the turns which are furthest from the wire to
the other mast. The idea being that the wire could move more freely
where it meets the tower and thus not be stressed at one particular
Any other ideas?
2. How to deal with radials
Not much room for radials. I can run one about 120 ft along or
under the ground right underneath the flat top. I can maybe mickey
mouse a few more about 20 ft long and that's about it. The fact
that I may have ground losses of 3 dB or so doesn't really trouble
me as almost no matter what I do it will be better than using the
80m dipole on 160. What does bother me is that about the only
sensible place to run the coax feed is right along the 120 ft
radial. I presume, then, that I'll have mucho current on the
outside of the shield and tons of RF in the house and shack.
I'm proposing to wind a coax choke at the base of the tower and
another one where the coax enters the house in hopes of suppressing
this shield current.
Any comments on the proposed installation would be greatly appreciated.
Lightning isn't an issue here, thank goodness.
73 and TIA for your help. See you (well, those few of you who will be
able to hear me) on 160.
Jim Smith VE7FO
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list