18
Pressurization and Startup
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 or an impedance bridge. If you don't
have access to low-power test equipment, 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 it off 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.
CAUTION
A high transmission line VSWR may indicate damaged transmis-
sion line and is likely to cause problems in the future, including
serious damage to your equipment.
Initial
Characterization
(recommended)
Should any problems arise later with your antenna, it will be extremely
helpful to know what the system’s characteristics were when it was
new. We recommend you perform the tests in this section after installa-
tion.
Step 1. Transmission
Line VSWR Reading
The first step is to characterize the transmission line by itself
a. Briefly disconnect the transmission line from the antenna system
input. Seal the antenna system input to prevent the entry of mois-
ture.
b. Terminate the coax transmission line in an instrument-quality 50-
ohm load.
c. Measure and record the voltage standing wave ratio (VSWR). File
this information with this manual for future reference.
d. The VSWR of the transmission line should be within the manufac-
turer's specifications. If it is, proceed. If not, you should call the
manufacturer before connecting the antenna. Problems must be
worked out with the design engineer on a case-by-case basis.
Summary of Contents for 6017
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