Antenna Revolution and RF Signal Processing

Antenna Revolution and Beam Selection

• During the second antenna revolution, the auxiliary beam selection is determined based on stored "I" logic in sectors with memorized data.
• In sectors with excessive clutter returns, new "I" logic is generated and combined with previous data, resulting in a stored "10*" digital word.
• Three binary words can be stored in memory for each cell: 00 (main beam), 01 (auxiliary beam), 10 (difference beam).
• Main beam is utilized in the second half of range; auxiliary or difference beams are available in the first half if enabled by the COMB/MAIN function push-button.

RF Signals Mixer and PRE-IF Amplifier

• The "Beam Combiner" signal mixes with the RF signal from the stabilized local oscillator (ST ALO) at a frequency of 30 MHz above the magnetron's transmission frequency.
• The mixed signal becomes an intermediate frequency (IF) signal, which is amplified by the PRE-IF AMPLIFIER before reaching the PACA circuit.

PACA Functionality

• Maximum clutter attenuation from the CLUTTER FIX is about 30 dB, with additional attenuation provided by STC circuits if needed.
• PACA adapts to incoming signals with three attenuation levels, PACA I, PACA2, PACA3, which are adjustable during setup.
• PACA operates in three modes: Adaptive, Programmed, and Adaptive + Programmed.
• A COHERENT OSCILLATOR (COHO) extracts Doppler information from echoes, minimizing transmitter frequency instability effects.

AFC Function

• Automatic Frequency Control (AFC) maintains constant transmitted signal frequency using a sample pulse derived from the transmitter circuit.
• Any frequency difference between the transmitted pulse and STALO is managed by an error voltage signal to adjust RF pulse frequency accordingly.

COHO Function

• This circuit captures phase information of transmitted RF pulses to compare against incoming echoes for Doppler information extraction essential for MTI operation.

AGC Function

• Automatic Gain Control (AGC) maintains consistent receiver noise levels at the input of the Moving Window Integrator, ensuring optimal performance.

BITE Function

• Built-In Test Equipment (BITE) in RF, IF, and video sections generates alarms for failures, allowing effective monitoring during operation.

RAM Program Store

• Activation of the RF CF Selection push-button is required to store CF LOGIC. Beam selection is based on clutter intensity in a sectorized map.
• Clutter returns exceeding the maximum MTI processable dynamic are counted and compared against a threshold to memorize high clutter information.

IF-MTI Function

• Amplification of the IF signal for phase detectors is facilitated by variable gain adjustments, ensuring correct signal levels for processing.

Phase Detectors Function

• The amplified IF signal is split into sine and cosine components for phase-shifting and detection using the AMPLITUDE-PHASE DETECTOR reference COHO signal.

PACA (Matched Filter) Function

• Matched filter maximizes signal-to-noise ratio, and both sine-cosine components undergo amplification and processing before AD conversion.

Disturbance Acknowledgment

• Disturbance type acknowledgment processes IF signals from omnidirectional and directional channels, utilizing 30 MHz DISTRIBUTORS for signal filtering.
• A malfunction indication system alerts about issues in individual assembly blocks; wide band and narrow band disturbances are analyzed separately.

BITE and Analogue Video Processing

• Tasked with generating stimulus signals for various strips, including those for the disturbance acknowledgment circuits, ensuring comprehensive system monitoring.

Explore the concepts of antenna technology, beam selection, and RF signal mixing. This quiz covers the second antenna revolution focusing on auxiliary beam logic and the functionality of RF signals in systems including mixers and amplifiers. Test your knowledge on these essential communication engineering principles.