Signal Management

Question 1

What is the difference between a Wire and a Cable?

Answer 1

A wire contains only one conductor, either a solid or stranded material, covered by an insulating sleeve.
A cable is a number of wires running parallel together, each individually insulated.
The cable may or may not be separately protected by an outer shield and/or jacket.

Question 2

How would the conductors in a wire or cable be described or classified?

Answer 2

Conductors are predominantly described by:
Material (eg copper)
Construction (ie solid or stranded)
Size

Question 3

What are the comparative advantages of solid and stranded conductors?

Answer 3

Solid conductors tend to be stronger than stranded equivalents, but are harder to bend and handle. Easier to manufacture, they would normally be cheaper than stranded.
Stranded cables consist of multiple thin strands, making the cable more flexible, but also more expensive, slightly thicker and less robust.

Question 4

What is flex life?

Answer 4

Flex life describes a cable’s resilience to constant movement, such as in a live event situation where cables are continuously set up and torn down.

Question 5

What is an insulator?

Answer 5

A insulator is designed to prevent two conductive materials from coming into contact and preventing the passing of current from one to the other.

Question 6

What is dielectric constant?

Answer 6

Dielectric constant is the ability of an insulator to prevent the flow of electricity between two conductive materials.
For accuracy, the term dielectric constant is now being replaced by Relative Permittivity.

Question 7

Why do some cables have an additional outer shield?

Answer 7

Cables can be specified with a shield which is designed to isolate the wires from electromagnetic and radio interference.

Question 8

Name three types of shield?

Answer 8

Foil sheild
Braided shield
Combination shield

Question 9

What is a Drain or Ground Wire?

Answer 9

A Drain wire is a bare wire which runs inside a foil shield, allowing the shield to be terminated at each end.

Question 10

What is a cable jacket?

Answer 10

The jacket is the outer layer of the cable that protects all of the inner cores.

Question 11

Why are cables with polyethylene jackets never used indoors?

Answer 11

Polyethylene is relatively inexpensive, but highly flammable, and therefore unsuitable for installation internally.

Question 12

Name a common material used for cable jackets that is suitable for use within buildings.

Answer 12

Teflon is designed to resist fire and works well indoors, but is more expensive than other materials.

Question 13

What is a coaxial cable (coax)?

Answer 13

Coaxial cable is an unbalanced cable, often used for short runs of video signals. There is usually a central insulated wire sheathed by an outer stranded layer. The central wire is usually the conductor with the outer shield acting as the return. Both conductors share the same axis, hence the name.

Question 14

What is the advantage of using Twisted Pair cables?

Answer 14

Twisted pair cables involve two individually insulated wires twisted around each other all along the length of the cable. The two cables are each exposed to the same interference, and by using balanced circuitry this interference can be removed.
Category 5 cable, for instance, has 8 separate wires (4 twisted pairs) surrounded by an outer foil and drain wire.

Question 15

What are the advantages of using fibre optic cables?

Answer 15

If digital signals are either on or off, then instead of an electrical current, optical fibre allows the transmission of light instead, with the light either on or off. The major advantage with sending light is that is is much less susceptible to external interference.

Question 16

What are the two main types of optical fibre?

Answer 16

Single mode or multi mode.

Question 17

What is an XLR connector?

Answer 17

An XLR connector is a push and lock pin connector.
It can be provided in 3 pin to 7 pin configurations.
3 pin XLRs are common for microphones, while 5 pins are the standard for digital lighting applications and many stereo headsets.

Question 18

What is a phone plug or jack plug.

Answer 18

Jack plugs have been the standard for consumer headphone devices for years, with the smaller 3.5mm jack becoming much more common in recent years due to the miniaturisation of audio devices, iPods, iPhones etc. The original 1/4 inch jack was designed for telephone switchboard operators in the late 1800s, and the “phone” term is more commonly still used in North America, where the 3.5mm jack is known as the 1/8 inch phone.

Question 19

What does the term TRS describe on an jack plug?

Answer 19

TRS stands for Tip, Ring and Sleeve, the standard three parts of a stereo jack plug. For stereo headphones to also provide handsfree speech for a mobile phone, they would require an additional connector ring, and would be described TRRS.

Question 20

What is an RCA connector?

Answer 20

RCA connectors are twin channel friction pressure connectors commonly used on consumer HiFi equipment and in many AV applications, primarily for sound and video. Also known as “phono” connectors, they are not to be confused with “phone” connectors, (otherwise known as jack plugs).

Question 21

Describe an F-Type connector.

Answer 21

F-Type connectors are used for coaxial cables, and have a single exposed wire core with the braided shield connected to a screw on outer ring. They are frequently used for antenna cables.

Question 22

What is a DB9A connector and what might it be used for?

Answer 22

A DB9A is a nine pin connector, sometimes used for video, but more increasingly now just for control connections, such as RS232.

Question 23

What is an RJ45 connector used for, and what is it also (more correctly) known as?

Answer 23

The Modular 8 Pin 8 Conductor is most frequently used for Ethernet connections, basically any common wired connection to a network, such as PCs, projectors and switches.
Sharing a similar shape to one of the original Registered Jack (RJ) connectors, it has since incorrectly become known as the RJ45 connector, even though the common wiring patterns do no the comply with the original RJ45 standard.

Question 24

What is a BNC connector?

Answer 24

A BNC connector is often used on component video, RF (e.g. antenna) connections, and for applications such as time and synchronisation.
A BNC is a small round coaxial twist to lock connector.

Question 25

What is a speakON connector?

Answer 25

A speakON connector is a rugged twist and lock connector favoured by the live music industry and ideal for situations that involve greater handling.

Question 26

What is a Captive Screw connection?

Answer 26

A captive screw is a simple connection where the conducting wires are clamped down by a screw. Often used for speaker connections and low voltage power supplies, they are not designed to be regularly disturbed.

Question 27

What is a Phoenix connector?

Answer 27

The Phoenix Combicon (brand name) is a small captive screw multi-cable connector. Once cables have been connected it is itself removable from the end equipment, making connection and disconnection quick and easy. It is frequently used for low output speaker connections and low voltage power supplies. Also known as the Euroblock, there are various other manufacturers, however the term “phoenix” is now generically used.

Question 28

What is a DVI-D connection?

Answer 28

Digital Video Interface was intended to provide a standardised digital interface for connecting displays, as a replacement for VGA.
DVI-D is a digital only 24 pin version, while DVI-I has an additional 5 pins (4 around a cross shape) and is also capable of supporting VGA.
DVI has largely been superseded by HDMI.

Question 29

What is a VGA connection?

Answer 29

For many years, VGA was the standard analogue video output from computers and laptops for running displays. Based on a three row 15 pin DE-15 connector, it is not designed to be hot swapped, as the ground pins do not automatically connect first, which may cause signal surges. Although still common, it is now largely being replaced by newer digital connections.

Question 30

What is HDMI?

Answer 30

High Definition Multimedia Interface (HDMI) has become a standard way of connecting digital displays to source devices, such as PC screens or projectors. As well as high quality digital video, it also transports high quality audio as well, removing the need for separate audio cables.

Question 31

What is a DisplayPort connector?

Answer 31

DisplayPort (and now Mini DisplayPort) are digital only video and audio connectors commonly used on laptops and other devices outputting video. It supports both video and audio.

Question 32

What is SDI and HD-SDI?

Answer 32

Serial Digital Interface (SDI) has been the broadcast industry standard for many years until being superseded by its High Definition version, HD-SDI.
It primarily uses coaxial cable with BNC connectors.

Question 33

What is USB?

Answer 33

Universal Serial Bus connections have been common on most Macs and PCs for years as a convenient digital way to connect storage and peripheral devices, replacing Serial connections.
With the latest version now able to run very high bandwidth, USB-C is now also starting to replace HDMI and Mini-DisplayPort on some new machines, as it can support high speed data, video, audio as well as charging power.

Question 34

How can grouping cable types together help to minimise interference?

Answer 34

Grouping cables together by signal types is a very effective way of preventing crosstalk, a problem where cables absorb electrical signals from nearby sources.
Aim to separate mic level, line, speaker, mains and high voltage cables and if necessary, aim to cross them at 90 degrees to each other.

Question 35

Apart from separating different cable types, what other steps can be taken to minimise signal degradation?

Answer 35

Avoid running near electrically “noisy” sources, such as fans, air conditioning units, motors, transformers etc.
Use balanced rather than unbalanced circuits, shielded cables, digital in preference to analogue, and fibre if possible.

Question 36

Why are distances important when planning cable runs?

Answer 36

All cables will lose signal as the distance from the source increases.
Understanding cable losses is important when planning cable types, amplification etc.
The effect will also vary depending on the frequencies involved.

Question 37

What is the difference between a switcher and a mixer?

Answer 37

A switcher selects a specific source to the output and excludes all others.
A mixer can send multiple input sources to the outputs simultaneously.

Question 38

What are the two main components of a matrix switcher?

Answer 38

Distribution amplifiers on each input and switchers on each output.

Question 39

How would you know how many switchers in a matrix switch?

Answer 39

The number of switchers is indicated by the number of outputs, i.e. a 4x2 matrix would have 2 switchers.

Question 40

Whats the difference between a mechanical video switcher and a smooth switcher?

Answer 40

A mechanical switcher physically disconnects and replaces the sources cable with a mechanical connection. Depending on the relative phase of the incoming new signal, there might be a noticeable drop in picture quality and sync as the change is made.
With a smooth switcher the new source is switched electronically, and looks for the ideal part of the signal phase to achieve a smooth transition.

Question 41

What is the interior width of an equipment rack?

Answer 41

19 inches. Most professional equipment is designed to fit in this enclosure.

Question 42

What is the standard measurement that the industry uses to measure the height of components in an AV or IT rack?

Answer 42

Devices are measured in rack units, which is about 1.75 inches or 44mm.

Question 43

What is a rack elevation diagram?

Answer 43

When planning a network, it is important to design the exact layout of the rack, including rack unit space for each component, as well as spaces for heat management, and logical cable runs. The rack elevation formalises this design.