Nautel FM10, Технические инструкции

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10 000 WATT FM BROADCAST TRANSMITTER
FM10
Page 6-7
15 November 1999
6.4.3.2 IPA Output Splitter: The IPA output
splitter section provides six equal, phase coherent
signals to drive the RF power modules. It is a six
way Wilkinson type hybrid realized with microstrip
transmission lines on a printed wiring board. The 50
ohm input impedance of each IPA input port is
transformed in two stages utilizing two quarter wave
38 ohm lines and two quarter wave 22 ohm lines to
arrive at a common point splitter impedance of 8.33
ohms. Each of the six 50 ohm output ports is
connected to an RF power module thru a length of
coaxial cable chosen for the frequency to provide the
proper IPA amplifiers output impedance
transformation, optimizing the isolation of the hybrid
power splitters within the RF power modules. Due to
their proximity and orientation to one of the quarter
wave 22 ohm sections of the splitter, resistors R15,
R17 and their associated stripline interconnection
provide a sample of the intermediate RF level for
external monitoring purposes at the
Int RF Level
Monitor output (J11).
6.4.3.3 IPA SWR Probe: The IPA SWR probe
section monitors the IPA module's RF output and
generates the
IPA Fwd Pwr (P11) and IPA Refld Pwr
(P12) outputs which are applied to the
control/monitor PWB for protection purposes. The
two RF inputs at J7 and J8 are connected to the
splitter section by a stripline transmission line. Due
to their proximity and orientation to the stripline, RF
voltages representative of the forward and reflected
power at the IPA output are induced respectively in
the forward power probe sections and reflected power
probe sections. The forward power output is peak
detected by CR1/C1 and CR4/C4 and combined at
R3 before being applied to J10. The reflected power
output is peak detected by CR2/C2 and CR3/C3 and
combined at R13 before being applied to J9.
6.4.4 RF POWER MODULE: See figure SD-
7. Each RF power module (A18 thru A23) provides
up to 1980 watts of RF output power and is
comprised of six 330 watt RF power amplifiers. The
RF input from the intermediate RF drive splitter
(A15) is split again on power module interface PWB
A13 to drive the six RF power amplifiers within the
module. An
Intermediate RF Level sample, for each
module, is applied to the control/monitor PWB. The
RF output of the six amplifiers is controlled by the
PA Volts supply from the AC/DC power supply. The
Temp and PA Fail outputs are applied to the
control/monitor PWB to sense excessive module
temperature and power amplifier failures. Refer to
the RF power module service instruction manual for
detailed information.
6.4.5 RF COMBINER/FINAL FILTER: See
figures SD-7 and SD-8. The RF combiner/final filter
A24 comprises two sections, impedance matching
and harmonic filtering. The 36 RF outputs from the
individual power amplifiers are applied to the
combiner thru coaxial cables W1 thru W36 which are
cut to make the electrical length from the amplifier's
power MOSFET drain to the combiner common point
a nominal 240
°
(at the carrier frequency). This
provides acceptable isolation between the amplifiers
in the event of a power amplifier failure. The
impedance matching section matches the 1.3889 ohm
(50/36) common point impedance to a nominal 50
ohms and provides attenuation of carrier harmonics.
A final filter composed of two tee sections provides
additional harmonic filtering.
6.4.6 RF POWER PROBE: See figure SD-8.
RF power probe A25 monitors transmitter forward
and reflected power and generates the
Fwd Pwr (J2)
and Refld Pwr (J3) signals which are applied to the
control/monitor PWB for protection and monitoring
purposes. The RF output from the RF combiner/final
filter is connected to final
RF Output J4 by a coaxial
type transmission line. Due to their proximity and
orientation to this line, RF voltages representative of
transmitter forward/reflected power are induced in
forward power probe PWB A1 and reflected power
probe PWB A2. Forward power output is peak
detected by A1CR1 and A1C1 and applied to J2.
Reflected power output is peak detected by A2CR1
and A2C1 and applied to J3. A nominal 50dB
RF
Monitor is also provided at J1 for use with a
modulation monitor or spectrum analyzer.