Mixed Deck — All GROL Topics Flashcards

How may a ship station identify itself during routine radiotelephone communications?

Answer: By the vessel's name or its assigned call sign

FCC Part 80 rules allow a ship station to identify using either the vessel's name or its FCC-assigned call sign.

Selectivity in a receiver refers to its ability to:

Answer: Discriminate between the desired signal and closely spaced interfering signals on adjacent frequencies

Selectivity is determined by the bandwidth and shape factor of IF filters; high selectivity allows the receiver to reject strong adjacent-channel interferers.

Which type of filter would be most appropriate for attenuating harmonic emissions from a transmitter final amplifier?

Answer: Low-pass filter

A low-pass filter installed at the transmitter output passes the fundamental frequency while attenuating harmonics, which are higher in frequency.

Neutralization of an RF amplifier stage is performed to:

Answer: Cancel unwanted feedback caused by the transistor's internal collector-base capacitance

At high frequencies, the transistor's internal capacitance feeds energy back from output to input; neutralization applies equal and opposite feedback to cancel this effect and prevent oscillation.

After establishing contact on Channel 16, vessels engaged in routine communications should:

Answer: Switch to an appropriate working channel

Channel 16 is used for initial contact and distress only; routine communications must be conducted on designated working channels.

What is the maximum allowed transmitter power for a ship VHF station on most channels?

Answer: 25 watts

Ship VHF stations are generally limited to 25 watts on most channels, with a minimum of 1 watt required on Channel 16.

What is the function of a squelch circuit in a VHF marine radio?

Answer: It silences the receiver output when no carrier signal is detected

The squelch circuit mutes the speaker when no signal is present, eliminating the annoying noise heard between transmissions.

Class AB amplifiers are preferred over Class B in high-fidelity audio applications because they:

Answer: Reduce crossover distortion while maintaining better efficiency than Class A

Class AB biases the transistors slightly into conduction, eliminating the crossover distortion of Class B while still being more efficient than Class A.

The amplification factor (μ) of a vacuum tube is defined as:

Answer: The magnitude of plate voltage change per unit grid voltage change needed to keep plate current constant

μ equals ΔVp/ΔVg (with opposite sign) at constant plate current and also equals the product of transconductance (gm) and plate resistance (rp).

A 4-bit binary ripple counter is clocked at 16 kHz. What is the output frequency at the most significant bit (Q3)?

Answer: 1 kHz

Each flip-flop in a ripple counter divides by 2, so a 4-stage counter divides by 16: 16 kHz ÷ 16 = 1 kHz at Q3.

What is the maximum Equivalent Isotropically Radiated Power (EIRP) for an EPIRB operating on 406 MHz?

Answer: 5 W

EPIRBs operating on 406 MHz are required to transmit at approximately 5 W EIRP to ensure reliable detection by the COSPAS-SARSAT satellite system.

An Exclusive OR (XOR) gate is a fundamental logic component. Which of the following statements correctly describes its output behavior?

Answer: The output is HIGH if an odd number of inputs are HIGH.

An XOR gate produces a HIGH (1) output when its inputs are different. For a two-input gate, this means one input is HIGH and the other is LOW. This logic extends to mean the output is HIGH only when there is an odd number of HIGH inputs.

The conduction angle of a properly biased Class A amplifier is:

Answer: 360°

Class A amplifiers are biased so the transistor conducts for the full 360° of the input cycle — the transistor never cuts off.

The DC current gain parameter hFE of a BJT is defined as the ratio of:

Answer: Collector current to base current

hFE (also called β) equals IC/IB and typically ranges from about 20 to 500 for silicon transistors; it quantifies how much the base current is amplified at the collector.

Two 10 μF capacitors are connected in series. What is the total capacitance?

Answer: 5 μF

For two equal capacitors in series, Cs = C/2 = 10/2 = 5 μF.

When using a hydrometer to check a lead-acid battery, what specific gravity reading indicates a fully charged cell?

Answer: 1.265 to 1.285 (fully charged)

A fully charged lead-acid battery cell has electrolyte with a specific gravity of approximately 1.265 to 1.285.

What is the function of a limiter stage in an FM receiver?

Answer: Removes amplitude variations from the IF signal

The limiter clips amplitude variations caused by noise before the discriminator, preventing noise from affecting the demodulated audio.

Which of the following receiver characteristics best describes its ability to differentiate between a desired signal and signals on adjacent frequencies?

Answer: Selectivity

Selectivity is the measure of a receiver's ability to reject unwanted signals on adjacent frequencies while receiving the desired signal. This is primarily determined by the quality and sharpness of the filters, especially in the IF (Intermediate Frequency) stages of a superheterodyne receiver.

What term describes the ratio of output power to input power in a transistor amplifier, expressed in decibels?

Answer: Gain

Gain (in dB) is 10 × log₁₀(P_out / P_in) and expresses how much the amplifier increases signal power.

How does the FM modulation index compare to the PM modulation index as audio frequency increases with constant audio amplitude?

Answer: FM modulation index decreases; PM modulation index remains constant

FM modulation index = Δf/fm, so it decreases as fm rises; PM phase deviation is proportional only to signal amplitude and is independent of modulating frequency.