FCC Commercial Element 8 pool, section 21

Subelement C

Receiving Systems

Section 21

Local Oscillators

821C1

The error voltage from the discriminator is applied to the:

Correct Answer
A.
Repeller (reflector) of the klystron.
B.
Grids of the IF amplifier.
C.
Grids of the RF amplifiers.
D.
Magnetron.

821C1

The error voltage from the discriminator is applied to the:

Repeller (reflector) of the klystron

In a klystron, the repeller or reflector is an essential component that helps control the electron beam and its interaction with the RF signal. The klystron is a microwave tube used in various applications, such as amplification and generation of microwave signals.

When an error voltage is applied to the repeller of the klystron, it alters the electric field strength inside the tube, which, in turn, affects the electron beam's velocity. This modulation of the electron beam's velocity helps in controlling and adjusting the output signal, ensuring stable and reliable operation of the klystron as an amplifier or oscillator.

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821C2

In a RADAR unit, the local oscillator is a:

A.
Hydrogen Thyratron.
Correct Answer
B.
Klystron.
C.
Pentagrid converter tube.
D.
Reactance tube modulator.

821C2

In a RADAR unit, the local oscillator is a:

Klystron.

In a RADAR unit, the local oscillator is typically a "Klystron." A klystron is a type of vacuum tube used as a microwave amplifier or oscillator. It generates a stable microwave signal that is then mixed with the received radar signal to convert it to an intermediate frequency (IF) for further processing and detection.

Mnemonic: "Keep Laughing, You've Seen The Radar On!"

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821C3

What component of a RADAR receiver is represented by block 48 in Fig. 8A1?

Correct Answer
A.
Klystron (local oscillator).
B.
Discriminator.
C.
IF amplifier.
D.
Crystal detector.

821C3

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821C4

What device(s) could be used as the local oscillator in a RADAR receiver?

A.
Thyratron
B.
Klystron
Correct Answer
C.
Klystron and a Gunn Diode
D.
Gunn diode

821C4

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821C5

The klystron local oscillator is constantly kept on frequency by:

A.
Constant manual adjustments.
Correct Answer
B.
The Automatic Frequency Control circuit.
C.
A feedback loop from the crystal detector.
D.
A feedback loop from the TR box.

821C5

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821C6

How may the frequency of the klystron be varied?

A.
Small changes can be made by adjusting the anode voltage.
B.
Large changes can be made by adjusting the frequency.
C.
By changing the phasing of the buncher grids
Correct Answer
D.
Small changes can be made by adjusting the repeller voltage and large changes can be made by adjusting the size of the resonant cavity.

821C6

To a large extent the Klystron's frequency is determined by the size of it's resonant cavity.

Small changes in the Klystron's frequency can be made by verying the repeller voltage.

The Repeller is one side of the cavity that can be negatively charged.

When the repeller is negatively charged it repels the also negatively-charged electrons oscillating in the cavity (hence the name), thus making the apparent size of the cavity smaller and the resonant frequency of the cavity, and the Klystron, somewhat higher.

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