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Fig. 5-6. The metallic shield of a coaxial cable permits it to be
run adjacent to, on, or through metal without affecting
the signal.
Installing Coaxial Cable
Because 75 ohm coaxial cable is shielded (Figure 5-6),
it is completely unaffected by contact with metal
structures, and it will not pick up unwanted signals as
twinlead does. Also, its performance is not affected
by moisture, and it generally has a much longer life
span than 300 ohm twinlead.
Aluminum/mylar-equipped coaxial TV cable provides
superior low-loss performance. (Examples are
Channel Master coaxial cable model numbers 9533,
9539, 9540, and 9544.)
Begin installing coaxial cable by first connecting the
"antenna end" to a balun. (The balun is not necessary
if the antenna is one of the few with a 75 ohm output.)
Attach the input lugs of the balun to the antenna
terminals. Apply acrylic insulator or silicone grease
to the connections. A weather boot (Figure 5-7)
should also be installed over the connections.
Next, run the coax through a standout mounted on
the boom or the mast. This will prevent the weight of
the transmission line from creating stress on the
antenna connections. From this point on however, the
coax may be taped to the mast at appropriate
intervals. Use plenty of good-quality vinyl tape to
secure it. (If you also are installing a rotor, sufficient
slack must be left in the transmission line between
the mast and the antenna to permit rotation of the
antenna. Also, coax and rotor wire can be run together
without interaction or signal distortion. See Chapter
22 for details about rotor installation.
These are precautions that must be observed when
installing coax:
1. Do not bend coax too sharply. This may collapse
the dielectric and ruin the necessary spacing
between the center conductor and shield.
S
I
ELECTING &
2. Do not crush or deform the coax. Ghosting and
smears may result.
3. When attaching connectors to coax, do not nick
the center conductor. This will cause a stress point
that will probably break the next time the wire is
flexed.
4. Remember that in almost all cases baluns are
required to match the 75 ohm coax impedance to
the 300 ohm impedances of the antenna output
and the TV input.
Fig. 5-7. A weather boot installed over the output connections
of an antenna.
GENERAL GUIDELINES FOR INSTALLING
TRANSMISSION LINE
Both coax and twinlead should be run as directly as
possible to the receiver. Avoid excessively sharp
bends or turns. You should also try to use one con-
tinuous transmission line without splices. (However,
if necessary, two lengths of coax can be joined with a
splicing connector (Figure 5-9). Also, keep the line
away from anything with sharp or jagged edges.
Fig. 5-8. A splicing connector should be used to join two lengths
of coaxial cable.
Run the transmission line into the house through an
attic or basement section if possible. Never run the
line through a window or door. This invites damage to
the line and is the mark of a careless installer.
If your entry is through shingles or shakes, remove
one of the shingles and drill a hole for the line
through the wall. Use a brace with an extension bit to
drill through the insulation, plaster, and/or drywall.
After you run the line through the hole, replace the
shingle, and you'll have a neat, waterproof entry.
T
NSTALLING
RANSMISSION
L
INE
17
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