Specifications

to Fault Sensing circuits. Both Buffer Amplifiers are continu-
ously operating and normally Predriver A is selected for opera-
tion. Fault Sensing therefore monitors Buffer A output, until
Predriver B is selected at which time Buffer B is monitored.
Should the Buffer Amplifier sample being monitored not be
present, a Buffer Fault will be sent to the Controller.
The same DC voltages are applied to a Sample Buffer that
provides a Buffer Sample for metering purposes.
An RF output sample is taken from the Driver Combiner Moth-
erboard for the active Predriver A or B and applied to a Fault
Sensing circuit. Should the active Predriver sample not be pre-
sent, a Predriver Fault will be sent to the Controller.
The same DC voltages are applied to a Sample Buffer that
provides a Predriver Sample for metering purposes.
E.5.7
Power Supply Temperature Sensing
The Power Supply Temperature Sensor Inputs, from the RF Amp
Power Supply rectifier heat sinks, are connected to Sensor Buff-
ers and then to the Power Supply Fault Comparators. If the heat
sink temperature should rise above a preset reference level, a
PowerSupply Temperature-FoldbackFaultwill be generatedand
the transmitter power output will automatically Foldback in
steps. If the heat sink temperature continues to rise, a Power
Supply Temperature-Off Fault will be generated and the trans-
mitter will shut off.
E.5.8
Power Supplies
An unregulated +22VDC is regulateddownto +15VDC, +8VDC
is regulated down to +5VDC, and -8VDC is regulated down to
-5VDC, to power circuits on the board.
A Fault Sensing circuit monitors these supplies and will generate
a Supply Fault for the Controller.
E.6 Detailed Circuit Description
Refer to the schematic diagram for the Driver Encoder board
(839- 7930-510) for all descriptions in this section.
E.6.1
Driver Amplifier Control
The Driver Amplifier control uses 2 PALS that provide the
turn-on/off control voltages for the 14 Driver Amplifiers. It is
used so that approximately 21Vp-p of RF drive is applied all 160
Big Step and Binary RF Amplifiers over the entire frequency
band. Drivers D1 though D7 are always turned on, Drivers D8
through D10 are frequency determined, and DriversD11 through
D14 are part of the AGC system.
E.6.2
L DRIVERS PAL
Refer to Figure E-1, L DRIVERS PAL, for the following discus-
sion.
NOTE
Many of the inputs to U7 are not being used by the PAL.
E.6.2.1
Predriver Control
Normally the PD_On input is logic high, and when the transmit-
ter is turned on, the TX On Enable input at J3 will go logic high.
The D0 output of the PAL will also be logic high and the
Predriver is turned on.
Whenever the Predriver Select switch S1 is changed, the PD_On
input will momentarily go logiclowand mute the Predriver while
the relays on the Driver Encoder are switched. The input will go
back logic high and the Predriver will be turned on again.
When the transmitter is OFF, the TX On Enable will go logic low,
and the Predriver is turned off.
E.6.2.2 Driver D1 - D6 Control
Whenever the +5VDC supply is present, the D1 through D6
outputs will be logic high. These Drivers will always be turned
on.
E.6.3
R DRIVERS PAL
Refer to Figure E-2, R DRIVERS PAL, for the following discus-
sion.
Figure E-1. L Drivers PAL
Figure E-2. R Drivers PAL
E-2 888-2339-002
WARNING: Disconnect primary power prior to servicing.