UBS Axcera 325A 500-Watt VHF Low-band Television Transmitter User Manual Chapter 4
UBS-Axcera 500-Watt VHF Low-band Television Transmitter Chapter 4
Contents
Chapter 4
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures
325A, Rev. 0 4-1
Chapter 4
Installation and Setup Procedures
There are special considerations that
need to be taken into account before the
325A 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.
4.1 Site Considerations
The transmitter requires an AC input line
of 220 VAC with a rating of 40 amps for
the exciter/amplifier cabinet. Make sure
that the proposed site for the transmitter
has the necessary voltage requirements.
The 325A 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 issues need to be resolved. The first
step is to determine the amount of heat
to be removed from the transmitter
room. 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 (350 watts) from the AC input
power (3500 watts). This number in
watts (3150) is then multiplied by 3.41,
which gives 10,741, the BTUs to be
removed every hour. 12,000 BTUs per
hour equals one ton, so a 1-ton air
conditioner will cool a 500-watt
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
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
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures
325A, Rev. 0 4-2
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
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 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
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 only
the front of the unit. Cooling air is
drawn in at 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 flow of cooling
air.
4. Interlocking the transmitter with
the air conditioner is
recommended to keep the
transmitter 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
transmitter.
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
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
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures
325A, Rev. 0 4-3
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 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. In those cases in which
transmitters are regularly off for a
portion of each day, a
temperature-differential 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
transmitter operation.
10. The blower should have two
speeds, which are thermostatically
controlled, and be 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 used, can not be
overemphasized.
13. Tube transmitters 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 5-
kW 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. A
combination of air conditioning and
ventilation should not be difficult to
design (see Figure 4-1). System
interlocking and thermostat settings
should be reviewed with Axcera.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures
325A, Rev. 0 4-4
As with any equipment installation, it is
always good practice to consult the
manufacturer when questions arise.
Axcera can be contacted at (724) 873-
8100.
Figure 4-1. 1 kW Minimum Ventilation Configuration
4.2 Unpacking the Cabinets and
Trays
Note: Air conditioning and any
related heat exhaust ducts should be
in place before continuing with the
installation of the transmitter.
Thoroughly inspect the cabinets and all
other materials upon their arrival. Axcera
certifies that upon leaving our facility the
equipment was undamaged and in proper
working order. The shipping containers
should be inspected for obvious damage
that indicates rough handling. Check for
dents and scratches or broken switches,
meters, or connectors. Any claims
against in-transit damage should be
directed to the carrier. Inform Axcera as
to the extent of any damage as soon as
possible.
Remove the cabinet and the trays from
the crates and boxes. Remove the straps
that hold the cabinet to the shipping skid
and slide the cabinet from the skid.
Remove the plastic wrap and foam
protection from around the cabinet. Do
not remove any labeling or tags from any
cables or connectors; these are
identification markers that make
assembly of the transmitter much easier.
Remove the two L-brackets, mounted on
the front panel rails, which held the trays
in place during shipment. The trays are
mounted in the cabinet using Chassis
Trak cabinet slides as shown in Figure
4-2. The tray slides are on the top and
the bottom of the VHF amplifier trays and
on the sides of the VHF exciter tray.
Inspect the trays for any loose hardware
or connectors, tightening as needed.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures
325A, Rev. 0 4-5
Figure 4-2. Chassis Trak Cabinet Slides
Open the rear door. Inspect the interior
of the cabinet for packing materials and
carefully remove any packing materials
that are found. Slowly slide each tray in
and out to verify that they do not rub
against each other and have no
restrictions to free movement.
4.3 Installing the Cabinets and Trays
It may be necessary to adjust the
position of the trays to keep them from
rubbing. This is accomplished by
loosening the cabinet slide mounting
bolts that hold the front of the slide to
the mounting frame of the cabinet and
moving the tray up or down, as needed,
to correct for the rubbing.
The air intake to the 500-watt
transmitter is only intended for room air.
The cabinet should be positioned for
adequate air intake and exhaust; the
opening of the rear door, if present;
access to the trays, including sliding
them out for testing; the main AC
hookup; and the installation of the output
transmission line. The cabinet should be
grounded using copper strapping
material and should be permanently
mounted to the floor of the site using the
holes in the bottom of the cabinet.
Once the cabinet is in place, and the
trays are checked for damage, the main
AC hookup can be made.
Caution: Before connecting the 220
VAC, make certain that all of the
circuit breakers associated with the
transmitter have been switched off.
The main AC input circuit to the 500-watt
transmitter should be a 40-amp, 230-
VAC line, using AWG 6 wire, inside of a
1-1/4-inch conduit.
The 220 VAC input connections are made
to terminal block TB1, which is part of
the AC distribution panel, near the upper
right-hand, rear portion of the
transmitter: terminals 1 and 4 (220 VAC)
and terminal 3 (chassis ground).
The output of the (A9) bandpass filter
assembly at (A5-J2), which is an “N”
connector, should connect to the
transmission line for the antenna system.
This completes the unpacking and
installation of the 325A 500-watt VHF
television transmitter. Refer to the setup
and operation procedures that follow
before applying power to the transmitter.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures
325A, Rev. 0 4-6
4.4 Setup and Operation
Initially, the transmitter should be turned
on with the RF output at (A9-A5-J2) the
coupler assembly terminated into a
dummy load of at least 500 watts. If a
load is not available, check that the
output of the coupler assembly is
connected to the antenna.
If the optional (A12) A/V input and
remote interface assembly is not present
in the system, connect the baseband
balanced audio input to the terminal
block TB1 or the composite audio input to
BNC jack J3 or J13 on the rear of the VHF
exciter. The baseband audio input can
remain connected when using the
(Optional) 4.5-MHz composite input, if
present, without affecting the operation
of the tray. Connect the baseband video
input to BNC jack J2 or J1 also on the
rear of the VHF exciter or, if the
(optional) 4.5-MHz composite input kit is
purchased, connect the 4.5-MHz
composite input to BNC jack J2 or J1. To
use the 4.5-MHz composite input, the
4.5-MHz composite input must be
connected to J2 or J1 and the baseband
select must be removed from J7-6 and
J7-7 on the rear of the tray. To use the
baseband video and audio inputs, the
baseband video input must be connected
to J2 or J1, the baseband audio must be
connected to the proper jack, and the
baseband select must be connected from
J7-6 and J7-7.
If the optional (A12) A/V input and
remote interface assembly is present in
the system, the baseband balanced audio
input connects to the terminal block TB1
or the composite audio input to BNC jack
J6. The baseband audio input can remain
connected when the 4.5-MHz composite
input is in use without affecting the
operation of the tray. Connect the
baseband video input to BNC jack J2 on
the A/V input and the remote interface
assembly or, if the (optional) 4.5-MHz
composite input kit is purchased, connect
the 4.5-MHz composite input to BNC jack
J2. To use the 4.5-MHz composite input,
the 4.5-MHz composite input must be
connected to J2 and the baseband select
must be removed from J7-6 and J7-7 on
the rear of the VHF exciter tray. To use
the baseband video and audio inputs, the
baseband video input must be connected
to J2, the baseband audio must be
connected to the proper jack, and the
baseband select must be connected from
J7-6 and J7-7 on the rear of the VHF
exciter tray.
Switch on the main AC, VHF exciter, and
the amplifier #1 and amplifier #2 circuit
breakers on the AC distribution panel
facing the rear of the cabinet and
mounted behind the rear door. On the
VHF exciter tray, switch the
Operate/Standby switch to Standby and
the Auto/Manual switch to Manual.
Normal operation of the transmitter is in
Automatic. Automatic operation uses the
video input to the VHF exciter as an
Operate/Standby switch. In Auto, if the
input video is lost for approximately 7
seconds, the transmitter will
automatically revert to Standby and,
when the video signal is restored, the
transmitter will quickly return to Operate.
Move the Operate/Standby switch on the
VHF exciter tray to Operate. Observe the
power supply reading, +48 V, on the
front panel of the VHF amplifier trays.
Note: If the transmitter does not
switch to Operate when the
Operate/Standby switch is placed in
Operate, check that an external
interlock plug, with a jumper wired
from pins 23 to 24, is connected to
jack J11 on the rear of the VHF
exciter. If (A12) the (optional) A/V
input and remote interface assembly
are present in the system, the
external interlock plug, with a
jumper wired from pins 21 to 22, is
connected to jack J9 on the
assembly.
On the VHF exciter tray, look at the front
panel meter reading in the % Visual
Power position; it should read 100%.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures
325A, Rev. 0 4-7
If necessary, readjust the screwdriver
adjust power pot on the front panel of
the VHF exciter for 100%. As the power
level is being checked, observe the meter
reading in the % Reflected Power
position. If the % Reflected Power is very
high, above 10%, a problem exists with
the output coaxial lines and they will
need to be checked. A center bullet
missing from the coax lines or loose bolts
on the connections can cause this
problem. Return the Operate/Standby
switch to Standby.
The gain and phase controls on the front
panels of the individual VHF amplifier
trays were adjusted at the factory to
obtain an output of 100% for the
transmitter and should not need to be
readjusted.
The front panel readings on the individual
VHF amplifier trays may not be the same.
Refer to the Test Data Sheet for the
transmitter to compare the final readings
from the factory with the readings on
each of the trays after the setup. They
should be very similar. If a reading is off
by a significant amount, refer to the
phasing and power adjustment
procedures for the VHF amplifier trays in
Chapter 5, Detailed Alignment
Procedures, of this manual before trying
to make any adjustments.
If a dummy load is connected to the
transmitter, switch the unit to Standby
and switch off the main AC circuit
breaker. Remove the dummy load and
make all of the connections that are
needed to connect the transmitter to the
antenna. Switch the main AC circuit
breaker on and the Operate/Standby
switch to Operate. Adjust the output
power screwdriver pot to achieve an
output of 100%.
If the transmitter is already connected to
the antenna, check that the output is
100%. If necessary, adjust the power
screwdriver pot.
This completes the transmitter setup and
operation procedures for the 325A VHF
low band transmitter. The transmitter
can now be operated normally.
If a problem occurred during the setup
and operation procedures, refer to
Chapter 5, Detailed Alignment
Procedures, of this manual for more
information.