User's Manual

Digital UHF Transmitter Chapter 3, Installation and Setup Procedures
DT835A, Rev. 0 3-1
Chapter 3
Installation and Setup Procedures
There are special considerations that
need to be taken into account before the
DT835A can be installed. For example, if
the installation is completed during cool
weather, a heat-related problem may not
surface for many months, suddenly
appearing during the heat of summer.
This section provides planning
information for the installation and set up
of the transmitter.
3.1 Site Considerations
The transmitter requires an AC input line
of 220 VAC with a rating of 20 amps for
the exciter cabinet and 100 amps for
each amplifier cabinet. Make sure that
the proposed site for the transmitter has
the voltage requirements that are
needed.
The DT835A is designed and built to
provide long life with a minimum of
maintenance. The environment in which
it is placed is important and certain
precautions must be taken. The three
greatest dangers to the transmitter are
heat, dirt, and moisture. Heat is usually
the greatest problem, followed by dirt,
and then moisture. Over-temperature
can cause heat-related problems such as
thermal runaway and component failure.
Each amplifier tray in the transmitter
contains a thermal interlock protection
circuit that will shut down that tray until
the temperature drops to an acceptable
level.
A suitable environment for the
transmitter can enhance the overall
performance and reliability of the
transmitter and maximize revenues by
minimizing down time. A properly
designed facility will have an adequate
supply of cool, clean air, free of airborne
particulates of any kind, and no
excessive humidity. An ideal environment
will require temperature in the range of
40° F to 70° F throughout the year,
reasonably low humidity, and a dust-free
room. It should be noted that this is
rarely if ever attainable in the real world.
However, the closer the environment is
to this design, the greater the operating
capacity of the transmitter.
The fans and blowers designed and built
into the transmitter will remove the heat
from within the trays, but additional
means are required for removing this
heat from the building. To achieve this, a
few considerations should be taken into
account. The first step is to determine
the amount of heat to be removed. There
are generally three sources of heat that
must be considered. The first and most
obvious is the heat from the transmitter
itself. This can be determined by
subtracting the average power to the
antenna (1500 watts) from the AC input
power (15,000 watts). This number in
watts (13,500) is then multiplied by
3.41, which gives 46,035, the BTUs to be
removed every hour. 12,000 BTUs per
hour equals one ton, so a 4-ton air
conditioner will cool a 1.5 kW digital
transmitter.
The second source of heat is other
equipment in the same room. This
number is calculated in the same way as
the equation for BTUs. The third source
of heat is equally obvious but not as
simple to calculate. This is the heat
coming through the walls, roof, and
windows on a hot summer day. Unless
the underside is exposed, the floor is
usually not a problem. Determining this
number is usually best left up to a
qualified HVAC technician. There are far
too many variables to even estimate this
number without detailed drawings of the
site showing all construction details. The
sum of these three sources is the total
amount of heat that must be removed.
There may be other sources of heat, such
as personnel, and all should be taken into
account.