User's Manual

8A535X03 Rev. Preliminary-00 Page 10 of 17
PRINCIPLE OF OPERATION
The OCR consists of four main blocks – Front End, IF section, Power Amplifier and Controller.
The Front End consists of band-pass filtering, low-noise preamplifier and adjustable PIN diode
attenuators. The sensitivity of the Front End is -113dBm.
After the Front End, the RF frequency is downconverted to an IF frequency by a mixer stage followed
by BP filtering, amplification and another mixer downconverting to a seconf IF frequency. This IF
frequency signal is filtered further by BP filters with BW depending on the programmed channel
spacing (25kHz or 12.5kHz respectively).
The IF signal path continues with an Automatic Gain Control Loop (AGC), which maintains constant
signal level, irrespective of the input signal level. The filtered and amplified IF signal goes through
selective filter, followed by a mixer, which further upconverts it to the programmed OCR transmit
frequency (same as the receive frequency). 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 20 Watts). The transmitted power level is compared and
adjusted to match its programmed value. The forward and reverse power is monitored continuously
and the output power is reduced when the forward and reflected power levels are outside of the
programmed range.
The Controller Board controls the operation of the OCR. It contains the microcontroller with Flash
memory for the firmware and EEPROM personality storage. Communications with the other modules
are facilitated by two RS-232, RS-484 and I2C serial links. One RS-232 serial port is accessible via
8-pin mini DIN connector on the front panel.
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.