User Manual

50289-BDA
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IF CHANNEL MODULE:
The IF module consists of 5 compartments:
• The RF amplifier provides for additional channel pre-selection of the received RF
signal.
• The down conversion of the signal received to an IF of 90Mhz, two cascade
crystal filters provides a high degree of filtering
• The hard limiting of the IF eliminates the requirements of an AGC loop. An
analog RSSI from the IF is compared to a threshold setting to produce a logic
output, RSSI KEY. This signal is monitored by the micro-controller to produce
the key line and key line time-out functions. Keying the final stages of the IF
module and the final RF power amplifier prevents unwanted spurious outputs
when no sign carrier is detected.
• The up conversion and filtering to the original frequency. With hard limiting at
the IF frequency, a constant output level verse the input level is produced.
• A dual output synthesized LO. Synchronized conversions mean that the frequency
received equals the frequency transmitted. The synthesizer output (Fc+90Mhz)
determines the channel frequency and is programmable in 12.5Khz steps to
produces the 25Khz channel spacing over the pre-selected band. The mother
board in the MACS slot of the card cage provides a 8Mhz common reference
oscillator to all the PLLs in the channel modules.
MICRO CONTROLLER:
The controller performs 4 functions:
• Programs the IF module synthesizer to the desired frequency and monitors lock
detect for a fault detection.
• Monitors the IF’s RSSI KEY and generate the key line function.
• Performs the key line time out and delay functions, of the time-out timer.
• Interface to the operator. Using a computer and AeroComm’s proprietary
software, the operator can program the channel frequency and time-out functions.
The software runs on Windows 95, 98, NT or 2000.
THE MOTHERBOARD:
The IF module and micro controller are configured as plug in modules. The mother
board routes the power and control signal between the modules, to the front panel
LEDs and RS232 connector and the card cage back panel.
RF POWER AMPLIFIER/8-WAY COMBINER:
The final RF power amplifier consists of a pre-driver amplifier stage and a hybrid class C
RF power module. The pre-driver adds additional filtering the channel modules output,
and amplifies to a sufficient level to drive the power amp. To shut-down the power amp,
the pre-drive amplifier is controlled (on/off) by the micro-controller output, key line,
from the associated channel module. To produce the required per carrier output level after
the power combiner, the low band channels utilize a 6 watt RF power module, and the
high band requires a 20 watt module. The outputs of the 8 RF power module both low
and high are summed by the 8-way combiner.