Shively Labs 6822, Инструкция по установке, эксплуатации и техническому обслуживанию, Страница: 53 / 78

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Retuning
8 Retuning
If you are re-using an existing antenna at a different frequency, or setting up
a used antenna at your site, you will need to retune the antenna to your
needs.
Before beginning
retuning:
Important
In the days before the hazards of intense RF power were realized, it was
common practice to have a technician climb the tower and adjust the
impedance match using the transmitter as a signal source and reading
the VSWR or return power on the transmitter. This practice MUST NOT
be used, as few transmitters can be operated at a low enough power
level to avoid exposing the rigger to an unsafe RF level. For reference,
see 29 CFR, Section 1910.97, the OSHA standard for exposure to non-
ionizing radiation.
To test and adjust VSWR safely, use low-power test equipment, such as
a network analyzer. If you don't have access to low-power test equip-
ment, please call Shively Labs before proceeding.
WARNING
Whenever a rigger is on the tower in the area of the antenna, shut off
the transmitter signal and lock and tag it out so that it cannot be turned
on accidentally.
Low-power test equipment should be used to prevent excessive radia-
tion exposure to the person doing the adjusting.
A high transmission line VSWR may indicate damaged transmission line and is
likely to cause problems in the future, including serious damage to your equip-
ment.
Setup
a. Adjust the arm lengths and feed straps to the settings in Figure 35 and Figure
36 . This is a good starting point.
b. Install the radiators on the tower leg or mounting pipe at the specified bay-
to-bay spacing (full-wave 118", half-wave 60". Special spacing in accordance
with specification - contact the factory if necessary).
c. Attach the feed cables to each bay in turn and dress cables along the tower
leg or mounting pipe (do not leave them hanging loosely in the RF field).
Attach the power divider near the bottom bay of the array using the saddle
"C" clamps and hose clamps. Coil the excess feed cables at the power divider
to the smallest diameter allowable with the minimum repeatable bend radius
for the cable being used.
NOTE
If the array is half-wave or special spaced the power divider input may
need to be slugged - contact the factory.