Metering - Harris ZX2500 Technical Manual

ZX Series
with non-standard ratio) is most likely to require the standard FM+HD mode as a
backup should the main transmitter fail. It is unlikely that it would require an HD-only
mode as a backup in a failure scenario. This made making the third mode HD-or-Split
Level a logical choice.
The transmitter adjusts the APC set point and forward power meter calibration
according its operating mode via the FM_MODE, FMHD_MODE (FM+HD),
HD_MODE logic lines to analog switches U6 and U8. These logic lines also activate
analog switches U9 and U10 to light front panel LEDs DS1, DS2, and DS3 to indicate
the current operating mode (page 6).
The FM_MODE line also activates analog switch U6A to shift the level of the PA bias
voltage generated by amplifier U28D. When the FM_MODE line is high, the output of
U28 shifts to the -5V level required for class C operation of the "IBOC" style PA
modules. Otherwise (FM+HD mode, HD mode, SL mode) the output of U28D is the
0V required for class AB operation.
This feature can be defeated by placing switch S16 in the off position, thereby causing a
0V bias while in the FM mode when using the optional "ZFM" style PA modules. (992-
9992-002 or 992-9992-902)
NOTE:
All new ZX amplifiers are supplied with HD-compatible "IBOC" modules unless
otherwise specified at time of purchase.
!
CAUTION:
"ZFM" AND "IBOC" PA MODULES ARE NOT COMPATIBLE AND CANNOT BE USED
SIMULTANEOUSLY IN THE SAME TRANSMITTER. BE SURE TO CHANGE THE
POSITIONS OF SWITCH S16 IF CHANGING FROM ONE MODULE TYPE TO
ANOTHER.

4.12.4 Metering

(page 5) The front panel meter is capable is displaying four operating parameters:
forward output power, reverse output power, PA stage voltage, and total PA stage
current. The determination as to which parameter is displayed is made by 4-by-1
analog switch U7, which is controlled by four-position ring counter U20. Pushbutton
S13 causes counter U10 to increase one count each time it is pressed. Resistor R85 and
C49 provide switch de-bouncing. The four possible output lines (Q0-Q3) control the
configuration of analog switch U7 and the on/off state of front panel indicator LEDs
12/20/11
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
888-2595-001 4-17