UBS Axcera 835A-6 6000-Watt UHF Transmitter User Manual 281869

UBS-Axcera 6000-Watt UHF Transmitter 281869

Site Considerations

835A 4 kW, 5 kW or 6 kW UHF Transmitter Site Considerations
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There are special considerations that need to be made before installing the 835A and this section will help you plan ahead.
The Transmitter 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 208/240 VAC,
Single Phase with a rating of 100 Amps . Check that the site has the voltage requirement needed.
The 835A 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 your 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.
To begin to design a suitable environment for your new Transmitter it is imperative that you understand what an "Ideal
Environment" is and how it can enhance the overall performance and reliability of your Transmitter, thereby maximizing
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 without excessive humidity. An Ideal Environment will require temperature in the range
of 40° F to 70° F year round, 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 your environment is to the Ideal Environment the greater the operational
elevation. A heat related problem may not surface for many months if the installation is completed during cool weather, but
may suddenly appear during the heat of summer.
The fans designed and built into your Transmitter will remove the heat from within the Trays but additional means are required
for removing this heat from the building. In doing this a few considerations should be noted. 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 it self. 'The following example is for a 5kW Transmitter. The heat can readily be determined
by subtracting the Average Power to the Antenna (3225 Watts) from the AC Input Power (20000 Watts). These numbers will
be different for the 4 kW and 5 kW Transmitters but can be found by referring to the published literature or directly from
Axcera. This number in Watts (16775) is then multiplied by 3.41 which gives (57202.75) the BTU's to be removed every
hour. 12,000 BTU's per hour equals one ton, so a five ton air conditioner will cool a 5 kW Transmitter. The second source of
heat is other equipment in the same room. Calculate this number as you did above. 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.
Now that you know the amount of heat that must be removed we will consider how this can be accomplished. Your options
are air conditioning, ventilation or a combination of the two. Air conditioning is always the preferred method and is the only
way to approach the Ideal Environment.
Ventilation will work quite well if the ambient air temperature will be below 100° F or about 38° C and the humidity should be
at a reasonable level. In addition, the air stream must be adequately filtered to ensure that no airborne particulate of any kind
will be carried into the Transmitter. 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 air conditioning year round
is not feasible for whatever reason. However, operation of air conditioning and ventilation simultaneously is not
recommended because 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.
A few precautions should be observed concerning an air conditioning system.
1. Air conditioners have an ARI nominal cooling capacity rating. In selecting your air conditioner do not assume you
can equate this number to your requirements. Make certain that your contractor uses the actual conditions you wish to
maintain in determining the size of the unit. With desired conditioned room temperature under 80° F the unit must be
derated, possibly by a substantial amount.
835A 4 kW, 5 kW or 6 kW UHF Transmitter Site Considerations
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2. Do not have the air conditioner blowing directly onto the Transmitter. Condensation may occur on, or worse, in the
Transmitter under certain conditions.
3. Do not isolate the front of the Transmitter from the back with the thought of air conditioning the front only. Cooling
air is drawn in the front of all Transmitters and in the front and back of others. Any attempt to isolate the front from
the rear will adversely affect the cooling air flow.
4. Interlocking the Transmitter with the air conditioner is recommended to preclude operation of the Transmitter 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 which prevents the ingress of
dirt.
2. The inlet and outlet should be on the same side of the building, preferably the leeward side. The pressure differential
created by wind will be minimized. Only the outlet may be through the roof.
3. The inlet and outlet should be screened with 1/8" hardware cloth (preferred), 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 complete flushing of
heated air with no stagnant areas.
6. The filter area must be adequate to insure a maximum air velocity of 300 feet per minute through the filter. This is not
a conservative number but a never exceed 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. Where Transmitters are regularly Off for a portion of each day, a temperature differential sensor controlling 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 applies 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 Transmitter operation.
10. The blower should have two speeds, which are thermostatically controlled, and interlocked with the Transmitter.
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 present can not be overemphasized.
13. Tube Transmitters should not rely on the internal blower for exhausting cooling air at elevations above 4000 feet. For
external venting, the air vent on the cabinet top must be increased to an 8" diameter for a 1 kW Transmitter and to 10"
for 4, 5 kW, 6 kW & 10 kW Transmitters. An equivalent rectangular duct may be used but in all cases the outlet must
be increased in area by 50 % through the outlet screen.
14. It is recommended that a site plan be submitted to Axcera for comment before installation commences.
835A 4 kW, 5 kW or 6 kW UHF Transmitter Site Considerations
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In calculating the blower requirements, filter size and exhaust size, use the following guide. If the total load is known in Watts,
you will need 2000 CFM into 1/2" of water for each 5000 Watts. If the load is known in BTU's you will need 2000 CFM into
1/2" of water for each 17,000 BTU's. The inlet filter must be seven square feet minimum, larger for dusty and remote
locations, for each 5000 Watts or 17,000 BTU's. The exhaust must be at least four square feet at the exhaust screen for each
5000 Watts or 17,000 BTU's. The above is a general guide and may need modified for unusually severe conditions.
A combination of air conditioning and ventilation installation should not be difficult to design using the above information.
System interlocking and thermostat settings should be reviewed with Axcera. As with any equipment installation it is always
good practice to consult the manufacturer when questions arise. Axcera may be contacted at (724) 873-8100.

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