Key Topic 49: Audio & Squelch Circuits

Question 1

3-49F1: What is the digital signal processing term for noise subtraction circuitry?

A. Adaptive filtering and autocorrelation.
B. Noise blanking.
C. Noise limiting.
D. Auto squelch noise reduction.

Answer 1

A. Adaptive filtering and autocorrelation.

Question 2

3-49F2: What is the purpose of a de-emphasis in the receiver audio stage?

A. When coupled with the transmitter pre-emphasis, flat audio is achieved.
B. When coupled with the transmitter pre-emphasis, flat audio and noise reduction is received.
C. No purpose is achieved.
D. To conserve bandwidth by squelching no-audio periods in the transmission.

Answer 2

B. When coupled with the transmitter pre-emphasis, flat audio and noise reduction is received.

Question 3

3-49F3: What makes a Digital Coded Squelch work?

A. Noise.
B. Tones.
C. Absence of noise.
D. Digital codes.

Answer 3

D. Digital codes.

Question 4

3-49F4: What causes a squelch circuit to function?

A. Presence of noise.
B. Absence of noise.
C. Received tones.
D. Received digital codes.

Answer 4

A. Presence of noise.

Question 5

3-49F5: What makes a CTCSS squelch work?

A. Noise.
B. Tones.
C. Absence of noise.
D. Digital codes.

Answer 5

B. Tones.

Question 6

3-49F6: What radio circuit samples analog signals, records and processes them as numbers, then converts them back to analog signals?

A. The pre-emphasis audio stage.
B. The squelch gate circuit.
C. The digital signal processing circuit.
D. The voltage controlled oscillator circuit.

Answer 6

C. The digital signal processing circuit.