FCC Commercial Element 8 pool, section 11

Subelement B

Transmitting Systems

Section 11

Transmitting Systems

811B1

The magnetron is used to:

Correct Answer
A.
Generate the output signal at the proper operating frequency.
B.
Determine the shape and width of the transmitted pulses.
C.
Modulate the pulse signal.
D.
Determine the pulse repetition rate.

811B1

The magnetron is a type of vacuum tube used in microwave ovens and radar systems to generate electromagnetic waves at microwave frequencies. It operates as an oscillator, producing a continuous wave (CW) output signal at a specific frequency, typically in the gigahertz range.

Microwave ovens, for example, use magnetrons to generate microwaves, which are then directed into the cooking chamber to heat the food. The magnetron converts electrical energy into electromagnetic radiation, and its design allows it to generate the output signal at the desired operating frequency.

Mnemonic: "Magnetron Magic!"

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811B2

The purpose of the modulator is to:

A.
Transmit the high voltage pulses to the antenna.
Correct Answer
B.
Provide high voltage pulses of the proper shape and width to the magnetron.
C.
Adjust the pulse repetition rate.
D.
Tune the Magnetron to the proper frequency.

811B2

In electronics, to modulate means "to vary the amplitude, frequency or phase of a carrier wave in proportion to the amplitude of a source wave."

In the case of a RADAR transmitter, the carrier phase is modulated in amplitude to match the shape of the modulating pulse.

Amplitude modulation is acheived by varying the high-voltage supplied to the transmitter's output stage.

For RADAR Systems the output stage is the Magnetron, so the modulator varies the high voltage supplied to the Magnetron according to the shape of the modulating pulse and Answer B. is the right answer.

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811B3

Which of the following statements about most modern RADAR transmitter power supplies is false?

Correct Answer
A.
High voltage supplies may produce voltages in excess of 5,000 volts AC.
B.
There are usually separate low voltage and high voltage supplies.
C.
Low voltage supplies use switching circuits to deliver multiple voltages.
D.
Low voltage supplies may supply both AC and DC voltages.

811B3

Modern RADAR Systems are solid-state and no longer use Magnetrons, thus the high voltage required by Magnetrons is no longer needed and Answer A. is the right answer.

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811B4

The purpose of the Pulse Forming Network is to:

A.
Act as a low pass filter.
B.
Act as a high pass filter.
Correct Answer
C.
Produce a pulse of the correct width.
D.
Regulate the pulse repetition rate.

811B4

The PFN - Pulse-Forming Network produces pulses of the proper width so Answer C. is the right answer.

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811B5

The purpose of the Synchronizer is to:

A.
Generate the modulating pulse to the magnetron.
Correct Answer
B.
Generate a timing signal that establishes the pulse repetition rate.
C.
Insure that the TR tube conducts at the proper time.
D.
Control the pulse width.

811B5

The Synchronizer drives the PFN - Pulse-Forming Network to produce pulses at the proper repetition rate so Answer B. is the right answer.

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811B6

Which of the following is not part of the transmitting system?

A.
Magnetron.
B.
Modulator.
C.
Pulse Forming Network.
Correct Answer
D.
Klystron.

811B6

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