UBS Axcera 837B-5 User Manual

4-6 kW UHF Translator Chapter 3, Installation and Setup Procedures

Chapter 3

Installation and Setup Procedures

There are special considerations that
need to be taken into account before the
837B 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 translator.

3.1 Site Considerations

The Translator consists of three cabinet
assemblies, the Exciter Cabinet Assembly
and two Amplifier Array Assemblies. The
Exciter Cabinet Assembly requires an AC
Input of 208/240 VAC, Single Phase with
a rating of 20 Amps. Each of the
Amplifier Array Assemblies requires an
AC Input of 208/240 VAC, three Phase
with a rating of 55 Amps or Single Phase
with a rating of 100 Amps. Check that
the site has the voltage requirement
needed.

The 837B 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 translator 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 translator 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 translator
can enhance the overall performance and
reliability of the translator and maximize
revenues by minimizing downtime. 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 translator.

The fans and blowers designed and built
into the translator 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 issues need to be resolved. The first
step is to determine the amount of heat
to be removed from the translator room.
There are generally three sources of heat
that must be considered. The first and
most obvious is the heat from the
translator itself. The following example is
for a 5000 Watt Transmitter. The heat
can be determined by subtracting the
average power to the antenna (3225
watts) from the AC input power (20,000
watts). This number in watts (16,775) is
then multiplied by 3.41, which gives
57,202.75, the BTUs to be removed
every hour. 12,000 BTUs per hour equals
one ton; as a result, a 5-ton air
conditioner will cool a 5-kW 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 reviewing the detailed
drawings of the site that show all of the
construction details. The sum of these

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4-6 kW UHF Translator Chapter 3, Installation and Setup Procedures

three sources is the bulk of the heat that
must be removed. There may be other
sources of heat, such as personnel, and
all should be taken into account.

Now that the amount of heat that must
be removed is known, the next step is to
determine how to accomplish this. The
options are air conditioning, ventilation,
or a combination of the two. Air
conditioning is always the preferred
method and is the only way to create
anything close to an ideal environment.

Ventilation will work quite well if the
ambient air temperature is below 100° F,
or about 38° C, and the humidity is kept
at a reasonable level. In addition, the air
stream must be adequately filtered to
ensure that no airborne particulates of
any kind will be carried into the
translator. The combination of air
conditioning for summer and ventilation
during the cooler months is acceptable
when the proper cooling cannot be
obtained through the use of ventilation
alone and using air conditioning
throughout the year is not feasible.

Caution: The use of air conditioning
and ventilation simultaneously is not
recommended. This can cause
condensation in transmitters. For
tube-type transmitters, this can be
especially serious if the
condensation forms in the tube
cavity and creates damaging arcs.

The following precautions should be
observed regarding air conditioning
systems:

1. Air conditioners have an ARI
nominal cooling capacity rating. In
selecting an air conditioner, do not
assume that this number can be
equated to the requirements of
the site. Make certain that the
contractor uses the actual
conditions that are to be
maintained at the site in
determining the size of the air
conditioning unit. With the desired

conditioned room temperature
under 80° F, the unit must be
derated, possibly by a substantial
amount.

2. Do not have the air conditioner
blowing directly onto the
translator. Under certain
conditions, condensation may
occur on, or worse in, the
translator.

3. Do not separate the front of the
translator from the back with the
thought of air conditioning only
the front of the unit. Cooling air is
drawn in at the front of all
translators and in the front and
back of others. Any attempt to
separate the front of the translator
from the rear of the unit will
adversely affect the flow of cooling
air.

4. Interlocking the translator with the
air conditioner is recommended to
keep the translator from operating
without the necessary cooling.

5. The periodic cleaning of all filters
is a must.

When using ventilation alone, the
following general statements apply:

1. The blower, with attendant filters,
should be on the inlet, thereby
pressurizing the room and
preventing dirt from entering the
translator.

2. The inlet and outlet vents should
be on the same side of the
building, preferably the leeward
side. As a result, the pressure
differential created by wind will be
minimized. Only the outlet vent
may be released through the roof.

3. The inlet and outlet vents should
be screened with 1/8-inch
hardware cloth (preferred) or

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4-6 kW UHF Translator Chapter 3, Installation and Setup Procedures

galvanized hardware cloth
(acceptable).

4. Cooling air should enter the room
as low as practical but in no case
higher than four feet above the
floor. The inlet must be located
where dirt, leaves, snow, etc., will
not be carried in with the cooling
air.

5. The exhaust should be located as
high as possible. Some ducting is
usually required to insure the
complete flushing of heated air
with no stagnant areas.

6. The filter area must be large
enough to insure a maximum air
velocity of 300 feet per minute
through the filter. This is not a
conservative number but a never­exceed number. In a dusty or
remote location, this number
should be reduced to 150 CFM.

7. The inlet and outlet(s) must have
automatic dampers that close any
time the ventilation blower is off.

8. In those cases in which translators
are regularly off for a portion of
each day, a temperature­differential sensor that controls a
small heater must be installed.
This sensor will monitor inside and
outside temperatures
simultaneously. If the inside
temperature falls to within 5° F of
the outside temperature, the
heater will come on. This will
prevent condensation when the
ventilation blower comes on and
should be used even in the
summer.

9. A controlled-air bypass system
must be installed to prevent the
temperature in the room from
falling below 40° F during
translator operation.

10. The blower should have two
speeds, which are thermostatically
controlled, and be interlocked with
the translator.

11. The blower on high speed must be
capable of moving the required
volume of air into a half inch of
water pressure at the required
elevation. The free air delivery
method must not be used.

12. Regular maintenance of the filters,
if used, can not be
overemphasized.

13. Tube translators should not rely
on the internal blower to vent the
cooling air at elevations above
4000 feet. For external venting,
the air vent on the cabinet top
must be increased to an 8-inch
diameter for a 1-kW transmitter
and to a 10-inch diameter for 4, 5,
6 and 10-kW transmitters. An
equivalent rectangular duct may
be used but, in all cases, the
outlet must be increased by 50%
through the outlet screen.

14. It is recommended that a site plan
be submitted to Axcera for
comments before installation
begins.

In calculating the blower requirements,
filter size, and exhaust size, if the total
load is known in watts, 2000 CFM into ½
inch of water will be required for each
5000 watts. If the load is known in BTUs,
2000 CFM into ½ inch of water will be
required for each 17,000 BTUs. The inlet
filter must be a minimum of seven
square feet, larger for dusty and remote
locations, for each 5000 watts or 17,000
BTUs. The exhaust must be at least four
square feet at the exhaust screen for
each 5000 watts or 17,000 BTUs.

The information presented in this section
is intended to serve only as a general
guide and may need to be modified for
unusually severe conditions.

837B, Rev. 0 3-3