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Path: utzoo!linus!philabs!cmcl2!seismo!brl-tgr!tgr!d3unix!jhs@Mitre-Bedford
From: jhs%Mitre-Bedford@d3unix.UUCP
Newsgroups: net.ham-radio
Subject: Re: Roof Mounting a Beam Antenna
Message-ID: <213@brl-tgr.ARPA>
Date: Fri, 26-Jul-85 18:42:01 EDT
Article-I.D.: brl-tgr.213
Posted: Fri Jul 26 18:42:01 1985
Date-Received: Sun, 28-Jul-85 08:08:21 EDT
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Some comments:

1. Be very careful climbing around on your roof.  And on ladders on the way up
and down, too.  Also, be extremely careful to avoid having ladders or antennas
(or YOU) come in contact with power lines which may enter the house somewhere
near where you are working, or which may pass by your house near roof level.

2. One DISADVANTAGE of a roof-mounted antenna is that it might possibly
attract a lightning strike to your house.  A lightning arrester on the house
might be a good idea.  (This might be a good line of argument to get the XYL
to reconsider the tower issue!)  (Or maybe to reconsider her choice of OM.)
NOTE: A VERY effective lightning arrester can be made by taking a length of
very finely stranded welding cable and stripping it back 6 inches or so and
"fraying" the end of the wire into a bushy "head of hair" made up of the
individual tiny strands of wire.  This is mounted with the "hair" pointing
upwards, up high on your tower, above the beam if possible, and grounded to
the tower or else the heavy cable is itself run down the tower and to a good
ground system -- preferably several independent ground rods tied together.
Keep the grounding cable straight insofar as possible, as curves become
inductive and encourage lightning bolts to jump off for something nearby that
they like better.

According to Don Clark, a transient protection consultant used extensively by
FEMA (the Federal Emergency Management Agency), installations protected with
this "head of hair" approach simply NEVER have lightning strikes.  The fine
points of the wire cause such an intense electric field that the air around
them breaks down and leaks off the charge in little sparks rather than one big
one!  According to Don, you should give the gadget a "haircut" about once a
year, because little spherical beads of copper form at the ends of the fine
strands, indicating that they are carrying heavy currents at times.
Eventually this will decrease the E-field intensity at the ends and reduce the
protection the device gives.  Snipping off the little beads will restore its
performance.  Eventually you will of course have to use another piece of
welding cable to replace the used-up end.

3. If you are still not cowering in fear, you might find W6SAI's book
The Antenna Handbook a useful source of ideas on roof mounting.  The ARRL
Antenna Handbook also has some wisdom in it.  Basically, there are
little bitty sections of tower that are designed to go on a rooftop.
It is also possible to use TV mast for small beams.  Guy wires are a good
idea in either case.

4. Be careful what you attach to or guy to -- in a severe windstorm, it is
possible for a large, roof-mounted antenna to be stronger than the things
it is attached to and to pull off sections of roof or chimney or whatever.
(Another argument for your XYL!)

5. You might look into Dick Austin's itty-bitty little triband beam, which is
small and light enough to install very reasonably on a TV mast.  I believe it
uses twin-lead to feed it and requires a tuner and a balun, but it is possible
to run a short length of coax and put the balun outside the house if you have
problems running twin lead in and out.  This unit has about 4 to 5 dB of gain
over a dipole, and like all Austin antennas, this is what you would actually
measure on an antenna range.  The better small tribanders run 7 or 8 dB if
you are lucky, i.e. about a half S-unit better.  If you are lucky.
Austin is in Sandown, NH.  His mailing address is PO Box 357, ZIP is 03873.
His phone is (603) 887-2926.

Dick will probably also be willing to give you good information on which
competitors' antennas are reasonably good if you choose to pick one which is
coax-fed.  He tends to be very helpful and objective when it comes to
discussions of antennas, although he of course would be happy to sell you one.

That's AT LEAST all I know, maybe a lot more!

						73,
						John S., W3IKG