X-band Solid State Transmitter Monitor User's Guide (TN-008)

This article describes the transmitter monitor board developed at CSU-CHILL. This board is designed for use in the Solid-state X-band project (WiBEX). The board monitors the operating conditions of the solid-state transmitter, and reports these to a higher-level controller. It can also shut down the transmitter in the event of a fault. The board is fully programmable via a Modbus/RTU interface.

Introduction

The transmitter monitor board is a critical component in the WiBEX radar design. Its primary task is to monitor the operating conditions of the solid-state transmitter. Secondary functions include a split power supply (+/- 5V) for the X-band microwave switches used in the front end of the WiBEX radar, a Peltier cooler driver for the X-band LNAs and a microwave switch driver.

Block Diagram

The figure below shows a block diagram of the board. The primary controller on the board is an Atmel ATMega164P microcontroller. This controller implements the main logic of the board, along with the Modbus/RTU slave logic. Various peripherals available on the microcontroller are used to interface to the analog electronics on the board.

Block Diagram

Modbus Registers

The interface to the synthesizer is through Modbus/RTU. The Modbus communications model is a single master controlling various slave devices. Each slave is addressable, and has different registers which may be read or written. This design implements read-only registers (referred to as Input Registers in the Modbus specifications) and read-write registers (Holding Registers). There are no coils or status bits available.

Input Registers

The available input registers are shown in the table below:

Register Number	Name	Description
1000	ALARM	Indicates the cause of any alarms indicated by the Modbus ALM signal. Reading the register clears the alarm condition and deasserts the Modbus ALM signal.
1001	STATUS	Indicates the operating status of the transmitter.
1002	TEMP_AMP1	Amplifier 1 temperature, in degrees C multiplied by 100.
1003	TEMP_AMP2	Amplifier 2 temperature, in degrees C multiplied by 100.
1004	FAN1_RPM	Fan 1 speed, in revolutions per minute.
1005	FAN2_RPM	Fan 2 speed, in revolutions per minute.
1006	FAN3_RPM	Fan 3 speed, in revolutions per minute.
1007	FAN4_RPM	Fan 4 speed, in revolutions per minute.
1008	V_AMP1	Amplifier 1 voltage, in millivolts.
1009	I_AMP1	Amplifier 1 current, in milliamperes multiplied by 10.
1010	V_AMP1	Amplifier 2 voltage, in millivolts.
1011	I_AMP1	Amplifier 2 current, in milliamperes multiplied by 10.
1012	TEMP_HOT	Peltier cooler hot-side (heatsink) temperature, in degrees centigrade multiplied by 100.
1013	TEMP_COLD	Peltier cooler cold-side (LNA) temperature, in degrees centigrade multiplied by 100.
1014	PFAN_RPM	Peltier cooler heatsink fan speed, in revolutions per minute.
1015	RP_COUNT	Reverse power pulses per second.

Input Register Map

Holding Registers

The available holding registers are shown in the table below:

Register Number	Name	Description
1000	DISP_MODE	Mode of the alphanumeric display.
1001	PA_CONTROL	Power amplifier power control.
1002	FAN_MODE	Power amplifier cooling fan mode.
1003	FAN_TGTSPEED	Target speed of the power amplifier cooling fans when in manual mode.
1004	FAN_P_FACTOR	Proportional gain for the fan speed control loop, when in automatic mode.
1005	FAN_I_FACTOR	Integral gain for the fan speed control loop, when in automatic mode.
1006	FAN_D_FACTOR	Differential gain for the fan speed control loop, when in automatic mode.
1007	RP_COUNT_LIMIT	Number of reverse power pulses per second needed to trigger an alarm.
1008	PELTIER_TEMP_SETPOINT	Temperature that the Peliter cooler tries to attain, when in closed loop (automatic) mode.
1009	PELTIER_P_FACTOR	Proportional gain for the Peltier cooler control loop, when in automatic mode.
1010	PELTIER_I_FACTOR	Integral gain for the Peltier cooler control loop, when in automatic mode.
1011	PELTIER_D_FACTOR	Differential gain for the Peltier cooler control loop, when in automatic mode.
1012	PA_VOLT_LOW	Lower limit of the acceptable power supply input voltage range.
1013	PA_VOLT_HIGH	Higher limit of the acceptable power supply input voltage range.
1014	PA_CURRENT_HIGH	Upper limit of the current that may be drawn at the power amplifier contacts.
1015	PA_TEMP_HIGH	Maximum power amplifier temperature.
1016	PELTIER_TEMP_HIGH	Maximum Peltier hot-side temperature.
1017	FAN_SPEED_LOW	Minimum rotation speed before a fan failure is declared.

Holding Register Map