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Subel. B
6 questions
Subelement B

Transmitting Systems

Section 14

Pulse Forming Networks Modulation

The pulse developed by the modulator may have an amplitude greater than the supply voltage. This is possible by:

  • Using a voltage multiplier circuit.
  • Correct Answer
    Employing a resonant charging choke.
  • Discharging a capacitor through an inductor.
  • Discharging two capacitors in series and combining their charges.

A Resonant Transformer stores energy in the LC circuit made-up by the inductance of it's coils and the inter-turn capacitance to store additional energy that can increase the output voltage of the transformer beyond the voltage defined by the ratio of turns of the secondary winding to the turns in the primary winding.

Answer B. is therefore the right answer.

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Pulse transformers and pulse-forming networks are commonly used to shape the microwave energy burst RADAR transmitter. The switching devices most often used in such pulse-forming circuits are:

  • Power MOSFETS and Triacs.
  • Switching transistors.
  • Thyratrons and BJT's.
  • Correct Answer
    SCR's and Thyratrons.

Thyratron valves and SCRs - Silicon-Controlled Rectifiers, their solid-state counterparts, are high-current, low insertion resistance, fast-switching active components ideal for PFNs - Pulse-Forming Newtorks, thus D. is the right answer.

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The purpose of the pulse-forming network is to:

  • Correct Answer
    Determine the width of the modulating pulses.
  • Determine the pulse repetition rate.
  • Act as a high pass filter.
  • Act as a log pass filter.

The PFN - Pulse-Forming Network is the circuit responsible for dtermining the width of the pulses, so Answer A. is the right answer.

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The shape and duration of the high-voltage pulse delivered to the magnetron is established by:

  • An RC network in the keyer stage.
  • The duration of the modulator input trigger.
  • Correct Answer
    An artificial delay line.
  • The time required to saturate the pulse transformer.

An artificial dealy line is used to tell the PFN - Pulse-Forming Network how long each pulse must last for, i.e. the width of the pulse, thus Answer C. is the right answer.

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Pulse-forming networks are usually composed of the following:

  • Series capacitors and shunt inductors.
  • Correct Answer
    Series inductors and shunt capacitors.
  • Resonant circuit with an inductor and capacitor.
  • None of the above.
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An artificial transmission line is used for:

  • The transmission of RADAR pulses.
  • Testing the RADAR unit, when actual targets are not available.
  • Correct Answer
    Determining the shape and duration of pulses.
  • Testing the delay time for artificial targets.

An artificial transmission line is used for determining the shape and duration of pulses.

An artificial transmission line, also known as a pulse generator or pulse forming network (PFN), is a specialized circuit used to shape and control the characteristics of electrical pulses. It is employed in various applications where precise pulse shaping is required, such as in RADAR systems, pulse power systems, or high-power laser systems.

The artificial transmission line works by controlling the propagation and reflection of electrical pulses within the circuit. By carefully designing the impedance and termination characteristics of the transmission line, it can be tailored to generate specific pulse shapes and durations.

This shaping capability is important because different applications require pulses with specific characteristics. For example, RADAR systems may require short and well-defined pulses for accurate range measurements, while high-power laser systems may require long-duration pulses for efficient energy transfer.

By utilizing an artificial transmission line, engineers can precisely control the pulse shape, duration, and other parameters to meet the requirements of the specific application.

Mnemonic: "Pulse Shaper"

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