23
Startup
6
Startup
Before Beginning
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 acci-
dentally.
Low-power test equipment should be used to prevent excessive radia-
tion exposure to the person doing the adjusting.
CAUTION
Although initial characterization is at your discretion, we strongly recom-
mend it as the best way to identify both initial problems and possible
future system damage.
CAUTION
A high VSWR may indicate damaged transmission line and is likely to
cause problems in the future, including serious damage to your equip-
ment.
CAUTION
When pressurizing the system, never use a "garage" air compressor, as
it will not clean the air and will blow both moisture and contaminants
such as oil and graphite into the coaxial system.
Be sure to use a good quality pressure gauge which will read accurately
in the 5 - 20 psig (35 - 135 kPa) range; don't depend on the cylinder
gauge, which will not be accurate at a low pressure.
Do not raise pressure over 20 psig (~135 kPa), even briefly. Note that it
takes time for the entire system to fill with the new pressure and the
pressure gauge to stabilize.
Important
Shively Labs will not accept responsibility for antenna failure after opera-
tion without proper purging or positive pressure of dry air or dry nitro-
gen.
CAUTION
If all moisture is not removed from the interior of the system, it will con-
dense when the weather cools. The condensed moisture (water) will
cause arcing and permanent physical destruction of the coaxial system,
including the transmitter output network.
