User's Manual

Principle of Operation
The CMD consists of four main blocks – Front End, IF section, Power Amplifier and
Controller.
The Front End consists of band-pass filtering and low-noise amplifier. The sensitivity of the
Front End is -120dBm.
After the Front End, the RF frequency is downconverted to 109.65MHz by a mixer stage
followed by BP filtering, amplification and another mixer downconverting to IF 450kHz.
The IF signal path continues with an Automatic Gain Control Loop (AGC), which maintains
constant signal level, irrespective of the input signal level. The processed signal is fed to a
modulator and Upconverter. The upconverted signal (110.520MHz) goes through selective
filters and amplifier stages, followed by a mixer, which further upconverts it to the
programmed CMD transmit frequency (same as the receive in the OCR or different
frequency in the Translator mode). The transmit frequency signal is fed to the power
amplifier module where it is filtered and amplified. The driver and power amplifier produce
the programmed transmit power output (max 30 Watts).
The Controller Board controls the operation of the CMD. It contains the microcontroller
with Flash memory for the firmware, EEPROM personality storage.
The front panel RESET and TX DISABLE inputs are monitored and can be accesses via two
front panel holes with a round tool 2.5mm (0.1”) diameter. The front panel indicators (TX
DIS, DC ON, TX ON, RX ON, PWR and VSWR) are also controlled by the Controller
Board.
8A074X06 Rev. Preliminary Page 9 of 15
21/08/2003