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10 000 WATT FM BROADCAST TRANSMITTER

FM10

Page 2-3

01 October 2002

2.1.3.3

Power Consumption:

When operating at

11 000 watts RF output, power consumption is a
nominal 17.9kVA. It is recommended the ac power
source have a 25% over capacity (minimum rating of
23kVA) to ensure adequate regulation.

2.1.3.4

External Switching:

It is recommended

that all voltage carrying conductors from the AC
power source be controlled by an external switching
box that is located in close proximity to the
transmitter. This switch box should be clearly
marked

TRANSMITTER EMERGENCY ON/OFF

SWITCH

2.1.4

ANTENNA SYSTEM:

The antenna

system must present an impedance of 50 ±j0 ohms at
the carrier frequency. Circuitry within the
transmitter will begin to reduce the forward power
when the reflected power level reaches 440 watts
(1.5:1 VSWR relative to 11 000 watts forward
power). This will prevent damage to the transmitter
from high VSWR loads.

2.1.4.1

RF Feed Cable:

The feed cable

interconnecting the transmitter and the antenna
system should be a suitably rated coaxial cable. The
transmitter's RF output is configured to accept a
non-gas type 3-1/8 inch EIA flange (male)
connection. The RF feed cable's transmitter end must
be terminated by the appropriate male inner
connector (bullet) which is not provided with the
transmitter.

2.1.5

RF DRIVE SOURCE:

An exciter that

provides a frequency modulated RF drive in the 87.5
to 107.9MHz frequency band, at a nominal of 20
watts, into a 50-ohm load is required. A 19-inch
opening in the cabinet can be requested which will
accommodate Nautel's NE50 exciter. All other
exciters must be mounted externally. The exciter's
RF output cable (W39) is provided with the
transmitter. Any additional cabling required by an
external installation is not provided. The exciter
should contain an external on/off interlock or RF
mute capability. A set of form C contacts is provided
by the transmitter, at TB1 of the control/monitor
PWB (A14), as the exciter interlock/RF mute control.
If the exciter has an automatic level control (ALC)
circuit, it should be enabled, if possible.

2.1.6

SAFETY INTERLOCK:

The external

safety interlock circuit is connected between TB1-11
and TB1-12 on the control/monitor PWB (A14). It
must present a short circuit (low impedance) between
the terminals when the interlock circuit is intact and it
is safe to enable the RF output. It must present an
open circuit when any interlock switch has been
activated and the RF output is required to be
inhibited. Any number of serial interlock switches
may be installed.

NOTE

The RF output will be restored, at an exponential
rate, over a 250 millisecond period, after the
integrity of the external interlock has been restored.

2.1.7

REMOTE CONTROL CIRCUITS:

See figure 2-1. The on/off status of the transmitter's
RF power stage, RF power level control, and the
protection reset functions can be controlled from a
remote location, using switching circuits that comply
with the following:

NOTE

Remote control inputs have influence on transmitter
operation only when set to

REMOTE

. The external

control lines are interfaced with the transmitter
through opto-couplers located on the control/
monitor PWB (A14). A control input is activated
when +24V is present across its (+)/(-) inputs.

2.1.7.1

RF On Control:

This remote control

circuit must be the equivalent of a single pole,
momentary contact switch. The switch must be in
the 'closed' position when pressed and return to the
'open' position when released. The switch must be
connected such that, when activated, +24V is
connected between the

RF ON

(+)

(TB1-3) and

RF ON

(-)

(TB1-4) inputs. The operation of this remote

control will cause the transmitter to turn on.

2.1.7.2

RF Off Control:

This remote control

RF OFF

(+)