Mixed Deck — All CBT Topics Flashcards

What does a routing switcher (router) do in a broadcast facility?

Answer: Connects any input source to any output destination under software control

A routing switcher allows any input signal (video, audio, or data) to be connected to any output destination, providing flexible signal distribution throughout the facility.

In ATSC standards, what does the term 'subchannel' or 'multicast' refer to?

Answer: Multiple program streams within one 6 MHz channel

Multicasting allows a broadcaster to carry multiple program streams simultaneously within a single 6 MHz ATSC channel.

When measuring AC voltage with a true-RMS meter, what value is displayed for a 170V peak sine wave?

Answer: 120V

RMS voltage of a sine wave = Vpeak / √2 = 170 / 1.414 ≈ 120V, which is the effective heating value equivalent to that DC voltage.

What is the difference between drop-frame and non-drop-frame SMPTE timecode?

Answer: Drop-frame skips certain frame numbers to keep timecode aligned with real clock time at 29.97 fps

Drop-frame timecode compensates for the 29.97 fps rate (not exactly 30 fps) by skipping frame numbers 00 and 01 at the start of each minute, except every 10th minute, keeping timecode aligned with wall clock time.

What is the standard characteristic impedance of most coaxial transmission lines used in broadcast RF systems?

Answer: 50 ohms

50 ohms is the standard characteristic impedance for broadcast transmitter output and coaxial transmission lines, as it balances low loss and high power handling.

A technologist measures -10 dBu on an unbalanced consumer audio output but expects +4 dBu on a balanced professional input. What device is needed to interface them correctly?

Answer: Active balun or line-level matching transformer

A balun or active matching device converts the unbalanced consumer level to balanced professional level, correcting both impedance and level differences.

A technologist finds that an SDI signal passes correctly through a short cable but fails over a 100-meter run. What is the MOST likely cause?

Answer: High-frequency cable loss causing eye pattern closure at the receiver

Coaxial cable attenuates high frequencies; at 100 meters the serial digital signal's eye pattern may close enough to cause bit errors or signal loss.

A technician is working on an AC circuit for a transmitter and needs to calculate the capacitive reactance (Xc) of a 10µF capacitor at a frequency of 60Hz. What is the approximate capacitive reactance?

Answer: 265 Ohms

The formula for capacitive reactance is Xc = 1 / (2πfC). Plugging in the values: Xc = 1 / (2 * 3.14159 * 60Hz * 0.000010F), which calculates to approximately 265 Ohms.

A digital audio workstation outputs audio with periodic clicks and pops that correlate with hard drive activity. What is the MOST likely cause?

Answer: Insufficient CPU priority or audio buffer underruns caused by disk I/O contention

When disk I/O competes with audio processing for CPU resources, the audio buffer empties faster than it is filled, causing dropout clicks and pops.

What FCC rule requires broadcast licensees to file an environmental assessment before constructing a new antenna tower?

Answer: 47 CFR Part 1 Subpart I

47 CFR Part 1 Subpart I implements NEPA requirements, including environmental assessments for new antenna structures.

Which test instrument is used to measure the frequency response of an audio circuit?

Answer: Audio signal generator and analyzer

An audio signal generator sweeps frequencies while an analyzer measures the output level, producing a frequency response curve.

What does an Optical Time-Domain Reflectometer (OTDR) measure in a fiber optic plant?

Answer: Location and magnitude of losses and reflections along a fiber

An OTDR sends light pulses down the fiber and analyzes backscatter to pinpoint splices, connectors, breaks, and their associated losses.

What is the primary purpose of a transmission line in a broadcast RF system?

Answer: To transfer RF energy from the transmitter to the antenna with minimal loss

A transmission line's primary role is to efficiently transfer RF energy from the transmitter output to the antenna while minimizing losses due to reflection and attenuation.

What is the function of a transmitter in a broadcast system?

Answer: Converts signals into RF for broadcasting

A transmitter is a core component in a broadcast system that takes an audio or video signal (the program material) and converts it into a high-frequency radio frequency (RF) signal. This RF signal is then amplified and sent to an antenna for wireless propagation over the airwaves, enabling the broadcast of content to receivers. It is the device that generates the broadcast signal.

A broadcast station receives a Required Weekly Test (RWT) of the Emergency Alert System (EAS). What is the station's primary obligation regarding this test?

Answer: Log the receipt of the test.

FCC rules require that EAS participants log the receipt of Required Weekly Tests (RWTs). Unlike Required Monthly Tests (RMTs), stations are not required to re-transmit RWTs to the public. The purpose is to verify that the equipment can receive the alert.

In a modern broadcast facility, what is the process of combining multiple channels of digital audio with a serial digital interface (SDI) video signal into a single stream called?

Answer: Audio Embedding

Audio embedding is the process of inserting digital audio signals (such as AES/EBU) into the ancillary data space of an SDI video stream. This allows both video and up to 16 channels of audio to be transported over a single coaxial cable, simplifying wiring and ensuring audio and video remain synchronized.

In MPEG transport streams, what is the PID used for?

Answer: Packet Identification — uniquely identifies each elementary stream within the multiplex

The PID (Packet Identifier) is a 13-bit value in MPEG-2 TS packet headers that uniquely identifies which elementary stream each 188-byte packet belongs to.

FCC OET Bulletin 65 and its supplements provide guidelines for broadcast stations primarily to:

Answer: Evaluate compliance with Maximum Permissible Exposure (MPE) limits for human exposure to RF fields.

OET Bulletin 65 is the FCC's primary guidance document for helping stations evaluate whether their facilities comply with the FCC's safety limits for human exposure to radiofrequency (RF) electromagnetic fields. It provides methods for calculating or measuring RF fields to ensure they do not exceed the Maximum Permissible Exposure (MPE) limits for both the general public and occupational personnel.

What FCC rule specifies the maximum tolerance for a standard broadcast station operating above its authorized power?

Answer: +5% of authorized power

FCC rules allow AM stations to operate up to 5% above authorized power under normal conditions before a violation is cited.

When replacing a power amplifier tube in a high-power AM transmitter, which safety procedure is MOST critical before opening the final amplifier cabinet?

Answer: Discharge all high-voltage capacitors using a grounding stick

High-voltage filter capacitors in AM transmitters can retain lethal charges long after power is removed and must be safely discharged before work begins.