System Interconnect; Command Sharing - Harris ZX2500 Technical Manual

ZX Series
The system metering assembly provides a measurement of the final system RF forward
and reverse power level in larger model transmitters.
Forward and reverse power samples from directional couplers at the final system output
enter through SMA connectors J5 and J6. Networks R11-L1-C14-R5 and R12-L2-C21-
R6 provide frequency compensation to flatten the coupler response over the entire FM
frequency band. RMS detector ICs U1 and U2 convert the RF samples to a DC voltage
proportional to the square-root of the output power (voltage scaled). Operational
amplifiers U6C and U6D provide adjustable signal gain for meter calibration as set by
trimmer potentiometers R7 through R10. Potentiometers R7, R8, R9 provide meter
calibration for the FM, FM+HD, and HD modes respectively when switched into the
circuit by analog switches U6D, U6B, and U8C, as controlled by 2-bit decoder IC U3,
Q1, Q2, and the FM_ON abd HD_ON signals coming from the exciter over the system
bus.
Multiplier ICs U4 and U5 provide squaring of the forward and reverse DC samples to
provide meter readings proportional to power. Operational amplifiers U6A and U6B
provide buffered metering samples for remote control telemetry via the J1 REMOTE
connector and for the APC power control/web remote circuits in the individual PA
chassis via the J3 SYSTEM connector. Networks R91-R90-R19 and R94-R95 scale the
forward and reverse DC sample to a level appropriate for the front panel LED meters.
Additional connection lines for the on, off, raise, and lower commands are passed from
the system bus (SYSTEM) to the user system remote (REMOTE) and ultimately to the
remote terminal board in the rear cabinet area. This provides a convenient parallel
remote connection point for the user.
4.14 System Interconnect (multi-PA chassis transmitters)
In larger multi-PA chassis transmitters, multiple amplifier chassis are connected
together to function as a single transmitter. This interconnection is done in a way that
maximizes redundancy while simultaneously providing simple, intuitive operation.
The interconnection between chassis and the system meter assembly is provided by the
system bus. All PA chassis and the system metering assembly must be connected to the
system bus for the transmitter to operate properly.

4.14.1 Command Sharing

Consult Figure 4-1, below.
In each individual PA chassis, the on/off circuit (U13 on page 4 of 8010203541)
responds to a ground connection being presented by either the internal ON button, the
12/20/11
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
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