Specifications
includes a brief discussion of each device and references to other
sections of this manual where applicable.
4.3.1
Doors And Panels
Inner front and rear access doors and panels are secured with
quarter-turn fasteners, and tools are required to remove them.
4.3.2
Door Interlocks
Interlock switches have been installed on the inner front doors
and the rear hinged doors of the transmitter, all panels of the
power supply and the front panel and rear door of the output
cabinet. Control circuits will turn the transmitter OFF if any
interlocked door is opened. The transmitter must be manually
turned on again after the door is properly closed. For a descrip-
tion of interlock circuits and logic, refer to Section P, Transmitter
Interface board, and Section M, Controller board.
4.3.3
External Interlock
The External Interlock will turn off the transmitter the instant the
interlock continuity is opened. The External Interlock circuit
requires that the transmitter be turned back on manually after an
interruption. Refer to Section N, External Interface.
4.3.4
RF Amplifier Power Supply Discharging
The RF Amplifier PowerSupply consists of the +230 VDC,+115
VDC, and +60 VDC supplies. Each electrolytic supply filter
capacitor for these supplies has its own discharge resistor
mounted directly across the terminals of the capacitor. The
+230VDC and +115VDC supplies are also discharged by the
Crowbar Assembly, which connects these supplies to ground
through 2.5 Ohms of resistance whenever the OFF button is
depressed or the transmitter shuts itself off. Refer to the Crowbar
circuit description later in this section.
4.3.5
Mechanical Shorting Switches
When an inner front door or a rear hinged door is opened, heavy
mechanical shorting switches in parallel with the crowbar circuit
provide a direct path from the +230 Volt supply to ground.
4.4 Transmitter Protection
The following is a list of protection devices installed in the
transmitter. They are designed to protect the transmitter from
undesirable external conditions. It includes a brief discussion of
each device.
4.4.1
A/C Transients
MOVs (metal oxide varistors) are used to absorb transient volt-
ages on the incoming ac lines. Two are used on the single phase
feed, and three are placed across the 3-phase lines.
4.4.2
3 Phase AC Undervoltage And Loss Of Phase
An A/C line monitor K10 is connected to the 3 PH A/C input.
This monitor will turn off the transmitter in the event of a phase
imbalanceof8%orgreater,oriftheincomingvoltageis20%
less than the specified input.
4.4.3
3 Phase AC Overvoltage
If the 3 Phase A/C incoming voltage is too high, circuits that
monitor the RF Amplifier Power Supply +230VDC will turn off
the transmitter.
4.4.4
Single Phase AC Undervoltage And Overvoltage
IC voltage regulators on printed circuit boards include protection
against low regulated output voltages.
4.4.5
Air Flow Monitors
Dirty or clogged air filters, backpressure, or loss of a fan will
reduce air flow and therefore reduce cooling. Air Flow Monitors
are located in the Output cabinet, and Left, Center, and Right PA
Compartments. If the reduction of air flow is enough, the trans-
mitter will continually foldback power output until a safe oper-
ating level is reached. If air flow reduction is severe enough, the
transmitter will shut OFF.
4.4.6
Spark Gap
A spark gap at the transmitter’s RF output protects the transmitter
against high transient voltages caused by lightning or electro-
static discharge.
4.4.7
ARC Detectors
An upper ARC detector and lower ARC detector monitor the two
sections of the Output Network. Should an ARC occur, the fault
is treated exactly as a Network VSWR fault.
4.4.8
Discharge Ground
In the lower rear and upper front of the output network, discharge
sticks are provided for ensuring that any residual voltages have
been depleted. The discharge sticks should beremovedfrom their
respective mechanical clamps and used to short to ground capaci-
tors and other assemblies that may have collected an electrical
charge.
4.4.9
VSWR
If high VSWR is detected in the Network or Antenna, the
transmitter will foldback power until a safe operating level is
reached. If the VSWR is severe, the transmitter will shut off.
4.4.10
Temperature Sensing
Temperature sensors are attached to the heat sink of RF Ampli-
fier, RF1, and the rectifier heatsinks in the RF Amp Power
Supply. If the ambient air intake temperature increases above 70
degrees C, or the transmitter is severely mistuned, the heat sink
temperature will also increase. If the output of the sensor rises
above the preset threshold, the transmitter will foldback power
to a safe operating range. If the temperature increase is severe,
the transmitter will shut off.
4.5 RF Circuits In The Transmitter
4.5.1 RF Driver Section
The RF Driver section receives from the RF Interface board a
5Vp-p input signal (at the transmitter’s operating frequency). The
4-8 888-2339-002 12/16/03
WARNING: Disconnect primary power prior to servicing.