User Manual
AMPLIFIER CONTROLLER BOARD REV.5
PUB12-030 Rev. 1 Feb 14, 2013 12-030-21 Amplifier Controller Board Rev.5
5.2 POWER SUPPLY VOLTAGE AND CURRENT MONITORING
For the following description, refer to Figure 7 (Sheet #2 of the Schematic) in the upper section of the drawing for
the power supply monitoring circuitry. In the case of a MXi802 or MXi1002 the first section describing the on-
board current sensor is for reference only since sensing is done in the power supply chassis.
The MXi board has a built-in Hall Effect current sensor that is able to measure the current drawn by the RF
amplifier from the +50 volt power supply. The standard MXi low power transmitter would have a 50 amp current
sensor. For higher power transmitters, the power supply would be external to the amplifier chassis and is fitted
with its own current sensor telemetry that is fed into the MXi board separately and the MXi current sensor would
be left unused.
When the internal current sensing is being utilized, the MXi expects the +50V to be applied at connector E20. This
voltage is passed through a current monitoring circuit and then fed back out on pin E22 to the RF amplifiers.
When current passes through the sensor, then the output voltage would increase. When using U27 as the sensor,
jumper E4 must be placed in the INT position. The output of E4 is fed into the positive input of OpAmp U7B with a
potentiometer R15 is placed in the feedback path of U7A to allow the current to be calibrated.
When the power supply is external (usual in higher power MXi transmitters), the actual power supply is external to
the amplifier chassis and will then do its own current metering. In this configuration, the MXi board would not have
its own U27 current sensor installed but would receive this telemetry information from J5 pin 5. Jumper E4 selects
between the internal U27 sensing output or an external current sensor. When using the external sensor, jumper
E4 must be placed in the EXT position. OpAmp U7A allows for a gain control through potentiometer R15 so that
the current reading can be calibrated.
The Power Supply voltage is expected to be +50 volts DC +/- 0.5V and can be fed into the MXi board from one of
two points, depending on whether the supply is internal or external to the amplifier chassis.
When the power supply is internal to the MXi amplifier chassis, then the MXi expects the +50V to be applied at
connector E20. This voltage is passed through a current monitoring circuit and then fed back out on pin E22 to the
RF amplifiers. This configuration is used when the MXi is a lower power transmitter that can accommodate the
power supply internally.
When the power supply is external (usual in higher power MXi transmitters), the actual power supply is external to
the amplifier chassis and will then do its own current metering. The +50V sample is connected to J5 pin 6 (which
is in parallel with E20). Connector E20 is a higher current contact that would allow the current to be passed
through the internal current sensor U27. For an external supply these are not required and so both U27 and E20
will most likely not be installed on the board.
5.3 ON/OFF RELAY K1
The ON/OFF relay K1 and associated circuitry is shown in Figure 7. Relay K1 is a two-pole, single-side stable
relay that requires a constant voltage applied to its coil to maintain contact closure. The contacts of this relay
provide the control signals to activate the +50V power supply and the cooling fans.
There are two elements that determine if power is applied to the coil of K1. One is the +12V arming voltage on the
positive side of the coil that comes from the interlock chain. Three interlocks are placed in series with this coil
such that all three must be closed in order for K1 to receive its +12V arming voltage. The three interlocks are
Thermal, External #1 and VSWR Trip. If any of these interlocks are open, then the relay will not be energized and
transmitter amplifier will be shut down.
The second element that determines if power is applied to the coil of K1 is the control signal on the negative side
of the coil. This control signal can come from one or more of three sources.
The HCS08 CPU can always activate the coil from its PF5 pin. This pin activates the base of transistor U10B that
in turn will energize the coil of K1. The second source is the remote control TX_ON command at connector J6 pin
1. When jumper E7 is installed, the remote control TX_ON command can directly energize the coil of K1. The
third source is the front panel ON button. When jumper E5 is in the INT position, the front panel ON button when
pressed in will directly energize the coil of K1. For an MXi802 or MXi1002 the front panel ON button is mounted
in the power supply chassis, not the amplifier chassis and the remote control TX_ON command is disabled.