Nautel XL12 Technical Instructions Download Page 120

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12 000 WATT AM BROADCAST TRANSMITTER

XL12

Page 6-7

01 January 2002

6.5.3.6 Surge Arrestor Assembly:

The surge

arrestor assembly (A22A11) monitors the RF voltage
level at the combiner's common point. Whenever
this voltage exceeds 4000V peak (usually as a result
of a lightning strike), gas gap E1 fires. Current
transformer T1 monitors the current through E1 and
provides a

spark gap shutback

signal when the E1

fires.

6.5.3.7 Capacitive Divider Assembly:

The

capacitive divider assembly (A22A10) provides an
RF voltage sample to the

RF V SAMPLE

connector J1

on the exciter panel. When the RF output filter is
properly tuned, the RF voltage sample should lead
the current sample from the RF current probe
assembly (A22A9) by between 50ns and 120ns.

6.5.3.8 RF Current Probe Assembly:

The RF

current probe assembly (A22A9) provides an RF
current sample to the

RF I SAMPLE

connector J2 on

the exciter panel. When the RF output filter is
properly tuned, the RF current sample should lag the
RF voltage sample from the capacitive divider
assembly (A22A10) by between 50ns and 120ns.

CONTROL/MONITOR FUNCTION

6.6

The control/monitor function comprises the

power meter control PWB (A1A1), voltmeter control
PWB (A1A2), system control PWB (A1A3), remote
interface PWB (A1A4) and associated meters.
These PWB assemblies are located on the
transmitter's control/monitor panel, and provide local
and remote operational control and status monitoring
as well as the external interface for the transmitter
system (see figure SD-5).

6.6.1 SYSTEM CONTROL PWB (1A1A3)

(see

figures SD-1 and SD-5)

The system control PWB

controls the active exciter stage circuitry, interphase
PDM drive and RF power stage of the transmitter.
Its primary functions are:

Produces a DC voltage as the

carrier

reference

output that ultimately determines the

transmitter's RF carrier level. This voltage is
used as the reference voltage for a variable
pulse duration modulation (PDM) generator.

Monitors critical parameters and causes the

carrier reference

voltage to be turned off

(shutback) or reduced (cutback) when defined
fault threshold limits are exceeded

Identifies the out-of-tolerance parameter, when
the carrier level is shutback/cutback by
providing a visual indication for local monitoring
or an electrical status output for remote
monitoring.

Selects which exciter (

) will provide the

RF drive and variable pulse duration interphase
PDM drive to the RF power stage of the
transmitter.

Determines the on/off status of the
transmitter's RF power stage.

For a complete description of system control PWB
circuits, refer to the system control PWB instruction
manual.

6.6.2 RF POWER METER

(see figure SD-5)

The power meter control PWB (1A1A3) provides a
method for selecting desired RF power meter scale
as well as an indication of the scale used. Each time
the

SELECT METER SCALE

switch is pressed the

system control PWB toggles between the forward
power and reflected power selections.

6.6.3 DC VOLTS METER

(see figure SD-2)

The voltmeter control PWB (1A1A3) provides a
method for selecting desired voltmeter scale as well
as an indication of the scale used. Each time the

SELECT METER SCALE

switch is pressed the system

control PWB increments thru the meter selections.

6.6.4

REMOTE CONTROL CIRCUITS:

The on/off status, exciter selection and preset RF
power levels can be selected from a remote location,
using switching circuits that comply with the
following:

NOTE

The remote control switching circuits can be

configured to operate from either a differential

input (+24 VDC and return) or a ground return

for the remote interface PWB control lines.