I/O Filter Pcb - Harris ZX2500 Technical Manual

Section 4 Theory of Operation
The individual PA current samples from each half of the IPA module are summed in
amplifier U2A and passed to the IPA_CURRENT sample line via RFI network R40-
C13-R41 and J7-12.
Another noticeable difference with the IPA backplane, when compared with the PA
backplane is the alarm comparator threshold from voltage divider R45-R66 (R7-R70) is
+1.25V instead of +2.5V. This creates alarm thresholds of 83
14A instead of 24A. This is compatible with the typically lower power operation of the
IPA module halves.
4.7

I/O Filter PCB

Consult drawing 801-0203-551
The I/O filter board is located at the rear of the amplifier chassis and serves as the main
interface point for connections coming from the front panel controller, exciter, customer
parallel remote control, and other amplifiers when used in a multi-amp application.
It also converts RF forward and reverse power samples from the output assembly to DC
voltages via rms detectors U2 and U3.
CR1, CR2 & CR9 provide input voltage clamping for signal lines coming from other
amp chassis on SYSTEM INTERFACE bus J9. The SYSTEM INTERFACE bus
allows multiple amplifier chassis to be ganged together and all share the same on, off,
raise, lower, FM mode, HD mode, and power control commands. This allows multiple
power blocks to be stacked in parallel to reach power levels beyond 5kW. There are no
customer connection points on the SYSTEM INTERFACE bus.
Q2 through Q18 (except Q17) provide conversion from logic high or low levels to open
collector outputs for a variety of fault and status conditions at the customer parallel
remote control output J1.
Q1 provides a logic low to the exciter when a non-zero PA voltage is detected in this
amplifier chassis or any other amplifier chassis connected to the SYSTEM
INTERFACE bus. In this way, the exciter un-mutes when any one of multiple PA
chassis has PA voltage present (i.e. is ON) in a multi-amp configuration.
NOTE:
The input RF circuit has load resistors capable of safely dissipating the nominal
exciter input power when the transmitter is off and the fans are deactivated.
However, whenever possible, it is highly recommended the exciter mute function
be implemented as a safety precaution.
4-8
WARNING: Disconnect primary power prior to servicing.
888-2595-001
ZX Series
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12/20/11