Harris Gates Five 994 9204 002, Техническое руководство

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Filters. For further discussion on the opera-
tion of the PDM Amplifiers, refer to section
G.
The positive supply inputs of the PA mod-
ules are connected directly to the 260 volt
supply. The PA voltage is then increased by
pulling the low side of the PA toward
ground, and decreased by letting the low
side increase up to the same potential as the
high side (about 260 volts). The PDM am-
plifiers do this by varying their conduction
duty cycle.
PDM Amplifiers A6 and A7 provide out-
put for PA modules A1 and A4 (A4 is not
included in a GATES ONE).
PDM Amplifiers A8 and A9 provide out-
put for A2 and A3 (GATES FIVE only).
5.3.5.
PDM Loop
Refer to the PDM Loop diagram. This
shows the current paths for one specific
PDM amplifier circuit and the relationship
between the PDM, the PA, and the meter-
ing.
The drive signal from the PDM Generator
drives the PDM Amplifier transistors (Q19
and Q20) into switching operation via a
driver circuit on the PDM Amplifier.
During the ON portion of the 60 kHz
pulse, these transistors provide a low resis-
tance path for the PDM Filter to ground.
Current flows from ground, through Q19
and Q20, the fuses, the PDM Filter, and the
PA.
During the 60 kHz OFF cycle of the PDM
Amplifier transistors, current continues to
flow in the PA because of the stored energy
in the PDM filtering. On the input side of
the PDM filter, the voltage rises due to the
collapsing field around the PDM Filter coils
(otherwise known as flyback). This flyback
voltage then creates current flow in the
damper diode circuit.
The purpose of the damper diode is to
absorb the voltage overshoots by conduct-
ing them back into the high voltage supply.
The PA voltage is varied by the modulator
(PDM) section. This is done by varying the
low side of the PA with respect to ground.
Each PA transistor pair produces a square
wave in peak to peak amplitude equal to the
PA voltage.
Each half of a PA Quad operates 180
degrees out of phase, and provides this dif-
ferential to the primary of the toroidal trans-
formers. The secondaries of the toroidal
transformers are connected in series to the
input of the Output Network.
The PA Voltage is metered from the output
of the PDM Filter (or low side of the PA) to
the 260 volt supply (high side of the PA).
The PA Current is metered in line with the
260 volt line to the PA modules.
The Power Supply Current is metered in
the return side of the 260 volt supply.
Supply current is less than PA current as a
function of the PDM duty cycle. Supply
current is metering of the current out of the
260 volt power supply, and PA current is
metering of the current actually flowing in
the PA.
5.3.6.
RF Power Flow
The transmitter’s carrier frequency origi-
nates from the Oscillator (A16). The output
signal drives the Intermediate Power Am-
plifier (IPA, A5) with 1 to 2 watts of carrier
power. The output square wave of the oscil-
lator board is about 16V p-p typically.
The IPA amplifies the carrier signal to the
100-200 watt level and provides the Power
Amplifier modules (A1 and A4) with its RF
drive. The output of the IPA goes to the IPA
Output Network A26, which is a series
tuned LC filter. This filter is tuned to series
resonance and attenuates the harmonics of
the IPA drive signal so that a sinusoidal
waveform of the carrier frequency appears
at the input of the PA modules. The IPA
Output Network is connected to the PA
modules by the Splitter board which distrib-
utes the RF drive through a separate multi-
coax cable to the PA modules.
The RF is then amplified and modulated
on the PA modules. The PA Toroid boards
(A1A1 and A1A4) combine the RF power
from the individual amplifiers on the PA
modules and connect to the Output Network
(A21).
For a discussion on the theory and setup
of the output network, refer to Section D.
5.3.7.
Failsafe
The fail-safe interlock, the rear panel in-
terlock switches, the Airflow Sensor, and
the Phase Loss Monitor are in series with
the start contactor coil (K1). If the rear panel
interlock is broken the main contactors will
drop out thereby removing high voltage
power from the transmitter. The transmitter
will not come on if the rear panel interlocks
are broken or if the external interlock is
broken. No visible indication is provided to
display an open interlock, except that the
PDM Kill LED will be lit along with the
selected power level LED.
5.3.8.
AC Power Flow
Primary power for the high voltage cir-
cuits enters the transmitter at TB1 terminals
1, 2, and 3. It is then fed in parallel to A19K1
and A19K2. Step start action is obtained by
first energizing relay A19K1. This action
supplies the primary power through the step
start resistors A19R1, A19R2, and A19R3
to transformer A19T1. When relay A19K2
is energized, it shorts out step-start resistors
and supplies full AC power to transformer
A19T1. This action result in two clunks
produced by the contactors during transmit-
ter turn on.
Single phase AC power for the low voltage
circuits enters the transmitter at TB1 termi-
nals 5 and 6. It is then fed to circuit breaker
A20CB1. When A20CB1 is set to ON, the
load side of A20CB1 supplies AC power to
A20T1 which is the low voltage power sup-
ply transformer.
5.3.9.
High Voltage Power Supply
5.3.9.1.
Introduction
The GATES Series™ AM transmitters
contain power supplies with very low im-
pedance and high current capabilities with
large amounts of stored energy.
WARNING
DUE TO THE LARGE CURRENT CAPA-
BILITIES OF THESE POWER SUPPLIES
UNDER SHORT CIRCUIT CONDITIONS
EXTREME CAUTION SHOULD EXHIB-
ITED WHEN TROUBLESHOOTING AND
WORKING AROUND THIS TRANSMIT-
TER. ALWAYS DISCONNECT POWER BE-
FORE OPENING COVER, REAR PANEL,
ENCLOSURES, PANELS OR SHIELDS.
ALWAYS USE GROUNDING STICKS AND
SHORT OUT HIGH VOLTAGE POINTS BE-
FORE SERVICING. ENSURE DUST, DIRT
AND CHIPS ARE REMOVED FROM CABI-
NET BEFORE POWER SUPPLY OPERA-
TION IS STARTED. NEVER MAKE INTER-
NAL ADJUSTMENTS, PERFORM MAIN-
TENANCE, OR SERVICE WHEN ALONE
OR WHEN TIRED.
The purpose of the High Voltage Power
Supply is to supply the high voltage for
operation of the power amplifier and modu-
lator circuitry.
The main high voltage transformer is in-
stalled in the bottom of the cabinet with the
associated rectifiers on the wall directly
beside the transformer.
5.3.9.2.
Description
The GATES Series™ transmitter use full
wave bridge rectification. The rectified
voltage is capacitive filtered and no series
inductive choke is used. Resistors are con-
nected directly across the terminals of each
capacitor to provide slow discharge of a
capacitor in case the capacitor should not
get discharged by normal means.
Some transient protection is provided by
MOV’s (Metal Oxide Varistor) located at
the AC input and across the secondary ter-
minals of the transformers. The purpose of
these devices is to clamp the secondary
voltage at some voltage in excess of normal
Rev. T: Jan. 1996 888-2314-001 5-3
WARNING: Disconnect primary power prior to servicing.