Assembly Instructions

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.