Carver TX-11b Manual page 15

IT COULD FALL INTO POWER LINES! B) Make sure the antenna,
mast, and boom are properly grounded with a large conductor-wire
running from the antenna to a ground rod in as short a path as
possible.
NOTE: 10-gauge copper, 8-gauge aluminum, or 12-gauge copper-
clad steel wire should do the job. However, the heavier the better.
Certain masts can be grounded by a bar attachment to a ground rod,
with a strap as a connector. This is a superior ground attachment if
the mast's base rests on the ground, or special ground plate.
• Use stand off insulators to keep the ground wire away from the
house. Space these insulators four to six feet apart where practical.
It's a poor practice to staple the wire to your house.
• Use a proper antenna discharge unit or lightening arrester, mounted
as close as possible to where the feedline enters the house. Make
sure the arrestor/discharge unit is securely attached to the ground
rod with the heavy-gauge grounding wire, insulated with stand off
insulators along the house.
• NEVER ground the antenna (or anything) to a gas pipe. Make sure
any grounding scheme employing pipes in the house belong to the
water system. A lightening strike, instead of being harmlessly routed
to earth, can turn your home into an exploding sun.
• If your antenna and mast require the support of guy wires, make sure
the wires use in-line insulators between the guy wire and roof. These
insulators electrically isolate the support wires from the house. This
isn't a bad idea even if the guy wires are anchored to the earth.
• NEVER, NEVER work on any part of (and best keep completely away
from) your antenna system during an electrical storm! Remember to
disconnect your TX-11 b from the antenna during electrical storms,
too.
• Another important item related to personal safety is, of course, to
be careful when/if you start climbing around on roofs and the like.
Don't make your antenna installation be the set up for a quick fall.
Ground Rod
When it comes to the ground rod we've been talking about, this metal
rod should be driven deeply into the earth. A ground rod driven only
two feet down usually has three to four times the resistance of a
ground rod driven ten feet deep. That's the key: low resistance. The
object of all this grounding is to give a lightening strike the easiest
path to the earth, not your home. As we said, make sure you use a
lightening arrester or discharge unit that's attached to the ground rod
with the same heavy-gauge wire used from the antenna to the
discharge unit.
Between Antenna and Tuner: Feedlines
Last but not least in considerations for putting up an outdoor antenna
is the feedline which "connects" it all together. Earlier in the chapter,
we talked about the problems and merits of 300 0 twinlead and 75 (1
coaxial cable. There are some additional things that could relate to
your final choice between the two.
300 0 TWINLEAD: Remember, it's less expensive and has the lowest
line losses when dry, and properly insulated from the house and mast
with stand off insulators specially designed for twinlead. Twinlead
must also be kept away from metal gutters, window frames and other
wires. Of course, it should be kept well away from power lead ins.
There should be over an inch spacing between other wires in the
home and stereo system — more is better. Avoiding the obstacles
we've mentioned will add overall length to the lead in, and some of
these detours will cause additional line losses when wet. Also
remember that twinlead must be well insulated from the antenna mast,
house, etc. with stand off insulators. These insulators are available
in a variety of attachments: the shafts come terminated in screw-in
units, masonry nails for brick and concrete, and nail-ins to suit any
installation need. The stand offs should be used about every four feet
with twinlead. In addition, special care should be taken when running
twinlead through a wall, or bringing it indoors through a window frame.
Use a wall tube or frame bushing to isolate and insulate the twinlead
from the wall/frame materials. This can avoid possible signal loss and
interference problems at this point in the installation. If the total run
from the antenna to your TX-11 b exceeds 300 feet, a preamp at the
antenna might be needed to boost signals in the line.
75 n COAXIAL CABLE: Coaxial cable is the easiest of the two
feedline choices to install, and has some distinct advantages.
Obstacles that would seriously affect the performance of twinlead
can be virtually ignored, and since coaxial cable is shielded,
interference is much less of a problem. The only real drawback is the
cost, and the need of a preamp to boost signal in runs over 120 feet.
Actually, 120 feet is a pretty long way from your antenna to the tuner.
Also, since coax is easier to install, the cost of cable and preamp (if
needed) can be made up in a more effortless installation. Plus, the
benefits of lowered losses when wet, and reduced interference can
be an additional incentive to use coaxial cable. Coaxial cable can be
easily brought into the house to the tuner without the need of special
fittings or passages. Fewer stand off insulators can be used in an
installation using coaxial cable as a feedline: one about every six to
eight feet.
Some Additional Hints
• If you decided to chimney-mount the antenna, route the feedline
away from the chimney outlet by at least three feet. Heat, smoke, and
residue can break down the insulation of both twinlead and coaxial
cable.
• If you're planning to attach your antenna system to a chimney, make
sure the chimney has the structural strength to support it. Thoroughly
inspect the chimney for loose bricks, broken mortar, cracks, or other
conditions that could indicate a poor state of repair.
• DO NOT use a metal chimney stove pipe to support an antenna set-
up. Other than the considerations of structural support, a lightening
strike could turn your stove into a giant electrode. That can happen
with a metal pipe chimney, even if the antenna itself has been properly
grounded.
•For those who are located a considerable distance from any FM
transmitting facility, a tower or mast may be necessary to obtain better
line-of-sight and clearance for the antenna. If your outdoor installation
fits into this category, pre-made masts and tower kits are available
from many TV stores and electronic supply shops. Despite the cost,
a 30-to-50 foot mast or tower, in combination with a good high-gain
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