[TowerTalk] TowerTalk Digest, Vol 35, Issue 79
chief at thechief.com
Mon Nov 21 11:46:08 EST 2005
>Date: Sun, 20 Nov 2005 23:13:34 -0600
>From: "Jim Miller" <JimMiller at STL-OnLine.Net>
>Subject: [TowerTalk] Radials
>To: "TOWERTALK" <TOWERTALK at contesting.com>
>Message-ID: <032201c5ee5a$52c7a490$6600010a at hmjm500>
>Content-Type: text/plain; charset="iso-8859-1"
>Would the lightning protection provided with numerous bare radials fanned
>out on the surface of the ground from a ground mounted vertical antenna be
>greatly reduced or eliminated by using insulated radials instead?
>TIA, 73, de Jim KG0KP
Radials for lightning protection have different criteria than radials
for rf. So it's best to consider them separately. The reason why AM BC
stations can combine the functions is because they have enough money to make
the RF radials robust enough to perform the lightning protection as well.
You could do this in a ham radio installation but it would be massive
overkill in cost, materials, and labor.
Lightning radials are usually made of solid or stranded wire of #6 or
larger. There are usually 5 radials of up to 50 feet welded to ground rods
placed at intervals along the radials. All of this is shallowly buried to
keep people from tripping over the thick wire and ground rods. The wire,
rods, and welding jigs can add up to a lot of money. The labor adds up as
you dig the shallow trench, drive each ground rod and weld the rods to the
RF radials are a different story. You need somewhere between 20 to 60 of
them but fortunately, you can use really cheap insulated wire laid very
casually on top of the ground. You do not put ground rods along their
length. The biggest challenge for rf radials is just figuring out a good
way to lay them down cheaply and easily but not have people tripping over
them or sucking them up in your lawn mower.
By keeping these two as separate problems, you can put down a lot of cheap
rf radials, where you need lots of them. Then you can save your money for
the expensive materials and labor for the lightning radials.
Dudley - WA1X
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