Nautel FM10, Технические инструкции

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10 000 WATT FM BROADCAST TRANSMITTER
FM10
Page 6-1
15 November 1999
SECTION 6
THEORY OF OPERATION
GENERAL
6.1
The theory of operation for the subject
transmitter is presented in this section. Unique
circuits are explained.
TRANSMITTER DESCRIPTION
6.2
The transmitter operates at one fixed
frequency between 87.5MHz and 107.9MHz and
provides up to 11 000 watts of RF output power.
The transmitter may be operated locally where the
subject transmitter and studio are co-located or
remotely where the transmitter and studio are located
at different sites. For technical performance details,
refer to Table 1-1, Technical Summary. The
transmitter comprises three blocks (see figure SD-1);
AC/DC power supply, RF power stage and
control/monitor function.
AC/DC POWER SUPPLY
6.3
(See figures SD-2 and SD-3). The AC/DC
power stage converts the AC power source to a
positive DC voltage (PA volts) for the transmitter's
RF power amplifiers and to a second positive DC
voltage (IPA volts) for the IPA module. It also
provides the transmitter's regulated and unregulated
24 VDC and regulated ±15 VDC and +5 VDC
supplies. The AC/DC power supply comprises
power transformer A1T1, 3-phase rectifier
assemblies A2 and A3, chokes A1L1 and A1L2, low
voltage power supply assembly A26, fan assemblies
A27 and A28, power supply control PWB A5A1 and
switching power supply assemblies A6 thru A12.
6.3.1 POWER TRANSFORMER (A1T1):
See figure SD-2. The nominal 208/380/415 VAC
power source is applied to the primary windings of
step-down power transformer A1T1 through circuit
breaker A4CB1. Primary winding taps on A1T1
accommodate variations in the mean level of the AC
voltage.
6.3.1.1 Power transformer T1 has five sets of
secondary windings.
6.3.1.1.1 The 3-phase 'X' and 'Y' secondary
windings are the voltage source (54.9 VAC phase-to-
phase) for the B+ DC power supplies. The 'X' set is
delta wound and it supplies the
B+ volts (1) DC
power supply. The 'Y' set is wye wound and it
supplies the
B+ volts (2) DC power supply. The
output of The B+ (1) power supply is applied to
50% of the RF power modules and the output of the
B+ (2) power supply is applied to the remainder.
This configuration results in any DC ripple frequency
on the RF output being twelve times the frequency of
the AC power source and will have less impact on the
signal to noise ratio.
6.3.1.1.2 The 3-phase 'Z' secondary windings are the
AC voltage source (18.9 VAC RMS phase-to-phase)
for the unreg24 VDC power supply which in
turn is the voltage source for cooling air fans and the
reg15/+5 VDC power supplies. It is
monitored by the 3-phase monitor PWB which
produces an alarm when a phase is lost.
3.6.1.1.3 The 36 VAC RMS 1-phase 'S' secondary
winding is centre tapped to provide 18-0-18 VAC as
the voltage source for the transmitter's regulated –15
VDC power supply.
3.6.1.1.4 The 1-phase 'A' secondary winding is
applied to AC receptacle J1 as the voltage source for
the exciter. It provides a nominal 115 VAC RMS
when the phase-to-phase voltage of the AC power
source is a nominal 208 VAC RMS (NASR92-02 is
installed). It provides a nominal 230 VAC RMS
when the phase-to-phase voltage of the AC power
source is a 380 or 415 VAC RMS (NASR92-03 is
installed).
6.3.2 THREE-PHASE RECTIFIER
ASSEMBLIES (A2, A3): See figure SD-2. Diode
pairs A2U1 to A2U3 and A3U1 to A3U3 form 3-
phase bridge rectifiers. They 3-phase rectify the 'X'
and 'Y' outputs of A1T1 and provide the
B+ volts (1)
and the B+ volts (2) outputs. Choke A1L1 and
A1L2 provide ripple rejection on the individual B+
Volts reservoir supplies. Current shunt resistor R1 in
the common B+ Volts Return for each B+ volts
output provides a DC voltage proportional to the
total DC current consumption of the transmitter.
Choke straps A1A1 and A1A3 provide B+ volts
samples for metering purposes.