Harris HTlFM - Page 14

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loads, air-handling systems, combining
equipment, etc. When this external contact
is opened, the transmitter will shut down or
will be prevented from coming up and when
this occurs the EXT
INTRLK
LED will
illuminate. After the external interlock
closes, the transmitter will come back up or
may
be
turned
on
and the
EXT
LED will be
extinguished. There is
no
memory to this
indicator. This external interlock command
interrupts the ac line contactor supply.
NOTE
The external failsafe interlock is a series
loop circuit. The external interlock must
provide a contact closure between termi-
nals 1 and 2 on terminal board TBJ on
the rear panel
of
the Controller chassis.
Automatic VSWR Foldback. The Con-
troller constantly monitors the reflected
power sample from the transmitter Direc-
tional Coupler.
If
the reflective sample ex-
ceeds
the
threshold
(adjustable),
the
Controller automatically lowers the EX-
CITER
drive which lowers forward output
power and the relative amount ofreflective
power detected
by
the Directional Coupler.
The Controller continues lowering output
power until the reflective voltage sample is
below the safe threshold level. The Control-
ler constantly monitors the reflective volt-
age level. When an antenna icing condition
begins to clear, and the load begins to return
to normal, the Controller automatically in-
creases power to the safest level. The auto-
matic
VSWR
foldback circuit does not
lower the antenna system
SWR,
that ratio
remains constant. The circuit merely lowers
forward
power
which
in
turn
simulta-
1-4
neously lowers reflective power to a safe
system operating level, thus keeping the
station on the air. This function is active
regardless
of
the selection
of
APC
ON
or
OFF.
Automatic Power Control. The Automatic
Power Control circuit is similar to the auto-
matic
VSWR
foldback circuit. After the
transmitter has been adjusted for desired
output power, the automatic power control
automatically maintains power to within
+/-5%. The Automatic Power Control may
be enabled or disabled by a switch in the top
cover
of
the
Controller.
For
example,
should a front panel
or
remote raise
or
lower
command be given, the transmitter power
will raise
or
lower. The Automatic Power
Control is only overridden by input from the
automatic
VSWR
foldback circuit which
will lower and maintain power at a safe
operating level under high-load VSWR
conditions.
AC Restart. AC Restart automatically re-
turns
the transmitter to its previous state
(either ON,
or
OFF) after an AC Power
failure. Except for the lock-up time
of
the
AFC loop in the Exciter, there is
no
warmup
delay at
TX
ON.
1.4.12.
Remote
Control
All connections are made on a large, easily
accessible terminal strip located on the rear
of
the Controller chassis. The following
control functions, meter samples, and status
indicators are all available for remote con-
trol and indication. These commands all
require a momentary contact closure be-
888-2312-001
tween the desired command line and Com-
mon (Chassis):
1.4. 12.1.
Remote Control Commands
1.
TXON
2.
TX
OFF
3.
POWER
RAISE
4.
POWER
LOWER
5. EBS Keying
1.4.12.2.
Remote Control Metering Sam-
ples
1.
PA
Voltage
2.
PA
Current
3. Forward Power
4. Reflective Power
1.4. 12.3.
Remote Status Indicators
1.
External Interlock Fault
2. Output Power Fault (Output power
less than threshold setting)
3. SWR FOLDBACK
4.
BALANCE FAULT
5. VSWR (ANTENNA)
When activated, these status outputs go
"low." Remote metering is typically a pos-
itive voltage. All remote indicators and con-
trols are "open collector, common ground"
compatible.
1.5.
Equipment
Characteristics
Table
1-1
lists the electrical operating
characteristics and parameters for the
FM
Transmitter as well as the mechanical char-
acteristics.
NOTE
Specifications subject to change without
notice.
WARNING: Disconnect primary power
prior
to servicing.