SRK FMA300, Руководство пользователя

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FMA 300 Manual
 2003 SRK Electronics Pty Ltd
Heatsink temperature is measured by the LM35, which produces a DC output voltage of
10mV/ºC. This voltage is also passed to the control board for metering and protection.
The output filter is a 9
th
order chebishev that provides at least 40dB of stopband attenuation at
175MHz and at least 60dB of stopband attenuation at 262.5MHz.
The RF output is passed to the output directional coupler via J3.
6.3
Control board
The control board is responsible for all measurement and protection functions. Refer to the
appropriate schematic.
The heart of the controller board is U1, a micro-controller unit. This performs the following
functions:
The analogue voltages representing the forward and reverse powers are digitised on pins 40
and 39. These values are then squared internally to allow the forward and reflected power to
be read on the front panel and via telemetry.
Other analogue parameters are connected to pins 33 to 38 as indicated on the schematic.
The push button used to select which parameter is displayed on the front panel is read on pin
17.
The two error conditions HIGH O/P and HIGH SWR are monitored on pins 20 and 21. These
signals are derived from the comparators U10 and U11. These devices monitor the forward
and reflected power control loops formed by U9B and U9C. If the output of U9B drops to less
than about 5V, this indicates that an over O/P power condition exists. Likewise U9C and a
high SWR condition.
U9B and U9C constantly compare the actual forward and reflected power with thresholds set
by VR3 and VR6 respectively. VR3 is set to the equivalent of about 330W of forward power.
VR6 is set to the equivalent of about 30W of reflected power. Either U9B or U9C can reduce
the bias voltage to the amplifier, thus reducing the output power. In this way, elegant and
seamless power and SWR protection are provided.
The forward and reflected RF voltages from the directional coupler are accurately converted
to DC levels by U7 and U8. U9A and U9D are used to scale these voltages so that 1000W
passing through the directional coupler provides 5.0V to the MCU.
A small value resistor in the supply line of the MOSFET on the amplifier palette generates a
voltages proportional to the drain current. This voltage is amplified and level shifted by U12,
Q2. VR11 is adjusted so that 20.48A of drain current produce 5.0V into the MCU.
Gate bias for the MOSFET is set by VR14.
Telemetry is provided by the on chip USART in the MCU, with U2 providing level shifting to
RS232 levels.
+10V for this board is provided by the small DC-DC converter, U14. U15 generates a
nominal -7V for the analogue circuitry.
The Front panel display is driven in a multiplex format by U1. Q1, 3, 5, 6 and 7 are all
switched on in turn, one at a time. Coincidentally, the appropriate segments are connected to
ground by U1. This happens several hundred times a second, giving the appearance of
constant brightness.