Receiving Systems
Receiving Systems
Detectors - Video Amplifiers
Which of the following statements is correct?
The Video Amplifier connects to the CRT - Cathode-Ray Tube, i.e. the display so Answer C.is the right answer.
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Video amplifiers in pulse RADAR receivers must have a broad bandwidth because:
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In video amplifiers, compensation for the input and output stage capacitances must be accomplished to prevent distorting the video pulses. This compensation is normally accomplished by connecting:
Remember ISI-IPO:
An Inductor in Series at the Input and and Inductor in Parallel at the Output.
Alternatively:
Always an inductor, in Series for Input, the Opposite for Output.
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Which of the following signals is not usually an input to the video amplifier?
The Resolver signals the bearing the RADAR antenna is pointing at. The antenna's bearing is not displayed on the screen, thus there is no need to have it amplified by the video amplifier and Answer A. is the right answer.
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Which of the following signals are usually an input to the video amplifier?
Range refers to the concentric circles on the RADAR display screen.
Brilliance is the general illumination level of objects displayed on-screen.
Contrast is the difference between the maximum and minimum illumination levels on the RADAR screen.
Thus Range, Brilliance and Contrast are all inputs to the Video Amplifier.
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The video (second) detector in a pulse modulated RADAR system would most likely use a/an:
The video (second) detector in a pulse modulated RADAR system would most likely use a/an:
Diode detector.
A pulse-modulated RADAR system transmits short pulses of radiofrequency (RF) energy and then listens for the echoes reflected from targets. These echoes contain information about the distance and characteristics of the targets. The received echoes are typically mixed with the local oscillator signal to down-convert them to a lower frequency, typically an intermediate frequency (IF).
After the down-conversion, the next step is to extract the modulating information or video signal from the IF. This process is carried out by the video detector. The video detector's primary task is to rectify the IF signal, effectively converting it from alternating current (AC) to direct current (DC). The DC output represents the amplitude variations of the IF signal, which carries the target information.
A diode detector is a simple and common type of video detector used in pulse-modulated RADAR systems. It employs a semiconductor diode as the rectifying element. When the IF signal is applied to the diode, it allows current flow only in one direction, effectively rectifying the signal. The rectified output is then smoothed using a capacitor, resulting in a DC voltage proportional to the amplitude of the IF signal.
Diode detectors are preferred for video detection in pulse-modulated RADAR systems due to their simplicity, low cost, and ability to handle the high pulse repetition frequencies (PRFs) commonly used in RADAR applications.
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