Skanti TRP 9250, Technical Manual, Page: 145 / 289

ANTENNA TUNING UNIT ATU 9250
ATU Board 945:
The ATU board comprises tuning network, measuring system and micro-controller circuits. The ATU
board matches the impedance of the antenna to 50 ohm in order to gain the best possible SWR.
The ATU board communicates tuning process and frequency information with the transceiver unit.
The tuning network consists of Capacitor Bank 1, Capacitor Bank 2, and an Inductor Bank. With
these it is possible to form either an L-network or a !-network The capacitor banks and inductor
bank are built up by binary related capacitors respectively binary related coils. The setting of
capacitance and inductance is accomplished by high current, high voltage RF reed relays. A current
detector at the antenna output terminal is used for measuring the antenna current for display at the
control unit. To prevent overload of the relays, current detectors are incorporated in the Inductor
Bank and in Capacitor Bank 2 and information fed back to the transceiver unit to decrease the
output power if maximum permissible current is exceeded. To prevent overheating a temperature
sensor is incorporated which at excessive temperatures commands the transceiver to reduce the
output power.
Dummy Load 741 (option):
The Dummy Load includes relays and load resistors. It permits two-tone alarm generator test into
dummy load to be performed as well as grounding or floating the antenna.
Dummy Load/Antenna Amp 742 (option):
The Dummy Load/Antenna Amp 942 includes relays, load resistors, and an RX-amplifier for fre-
quencies below 1.6 MHz. It permits two-tone alarm generator test into Dummy Load to be
performed as well as grounding or floating the antenna.
TECHNICAL DESCRIPTION ANTENNA TUNING UNIT ATU 9250
4-8 TRP 9250 TECHNICAL MANUAL