Modulation and Signal Types Flashcards

Which of the following is a primary advantage of Single-Sideband Suppressed-Carrier (SSB-SC) modulation compared to conventional Amplitude Modulation (AM)?

Answer: It requires significantly less bandwidth and transmitter power.

SSB-SC modulation improves efficiency by transmitting only one of the two redundant sidebands and suppressing the carrier wave. This reduces the required bandwidth by approximately half and concentrates the transmitter power into the information-carrying portion of the signal, making it more power-efficient than standard AM.

In Frequency Modulation (FM), what characteristic of the carrier wave is varied in direct proportion to the instantaneous amplitude of the modulating signal?

Answer: Frequency

The defining characteristic of Frequency Modulation (FM) is that the frequency of the carrier wave is shifted, or deviated, from its center frequency. The amount of this frequency deviation at any given moment is directly proportional to the amplitude of the input audio or data signal.

A technician is analyzing a transmitter that is emitting multiple signals simultaneously. Spurious signals are detected at frequencies that are the sum and difference of the original signal frequencies. What is this phenomenon called?

Answer: Intermodulation Distortion (IMD)

Intermodulation Distortion (IMD) occurs when two or more signals mix in a non-linear component, such as a power amplifier, creating unwanted new signals at frequencies that are mathematical combinations (sums, differences, and multiples) of the original frequencies. These can cause interference with other channels.

Which digital modulation technique involves sampling an analog signal, quantizing the sample's amplitude, and then encoding that value into a binary word?

Answer: Pulse-Code Modulation (PCM)

Pulse-Code Modulation (PCM) is a fundamental method of converting an analog signal into a digital signal. The process involves three steps: sampling the analog wave at periodic intervals, quantizing the measured amplitude of each sample to the nearest value in a range of digital steps, and then coding that quantized value as a binary number.

A J3E emission designator signifies what type of transmission?

Answer: Single-sideband, suppressed-carrier (SSB) voice telephony

According to the International Telecommunication Union (ITU) emission designators, 'J' indicates single-sideband, suppressed-carrier amplitude modulation. The '3' signifies a single channel containing analog information, and the 'E' indicates telephony, including sound broadcasting. Therefore, J3E represents SSB voice communications.

When comparing FM to AM for voice communications, what is a significant disadvantage of FM?

Answer: FM signals generally have a shorter effective range (line-of-sight) than AM signals at the same frequency.

While FM offers better noise immunity and audio quality, its signals are generally limited to line-of-sight propagation, especially at VHF and UHF frequencies. AM signals, particularly in the MF and HF bands, can travel much farther via groundwave and skywave propagation, giving them a longer effective range.