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TELECOMMUNICATION Reviews > Sound Test 8/11/16 > Flashcards

Sound Test 8/11/16 Flashcards

1
Q

What is the unit used to express sound intensity (sound pressure level)?

A

dB

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2
Q

What is meant by the term ‘resonant frequency’?

A

[The frequency at which an object will readily vibrate

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3
Q

What is the range of adult Audio frequencies?

A

30Hz to 15 KHz is the practical Adult range.]

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4
Q

What is the band of frequencies transmitted to, and received from a telephone?

A

300Hz to 3400Hz]

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5
Q

What is the dB SPL for the threshold of hearing?

A

zero dB

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6
Q

Sound intensity decreases according to the ‘Inverse Square Law’
Write a brief explanation of the ‘Inverse Square Law’

A

Sound level diminishes rapidly with distance. Twice the distance = one quarter as loud; quadruple the distance = one sixteenth as loud, and so on.]

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7
Q

What term describes the forward movement of air molecules?

A

compression

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8
Q

What term describes the backward movement of air molecules

A

Rarefactions (not refractions)]

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9
Q

What is the range of adult Voice frequencies?

A

[100Hz to 10 KHz]

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10
Q

Why does the wavelength of a sound wave change as it passes through different mediums?

A

[By definition wavelength is linked to velocity and the velocity of sound changes in different mediums.]

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11
Q

List four functions of a basic wireline telephone.

A
  1. Transmit speech.
  2. Receive speech.
  3. Dial the ‘B’ number.
  4. Audible indication of incoming call.
  5. ‘Off Hook’ indication to exchange.
    ‘On Hook’ indication to exchange.
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12
Q

What is the approximate dB SPL for the threshold of pain?

A

[≈130 dB]

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13
Q

What is the magnitude and type (ac or dc) of the telephone’s ring signal voltage?

A

[25Hz; ≈ 90Vrms ; 0.4s on - 0.2s off - 0.4 on - 2s null - repeat cycle]

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14
Q

How many frequencies does a complex wave, such as a square wave, contain?

A

[Two or more. (Or more than one)]

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15
Q

A transmitter converts ______ energy into electrical energy?

A

[Acoustic]

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16
Q

Which dialling type, decadic or DTMF allows interaction with the telephone network?

A

[DTMF]

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17
Q

List two types of telephony interaction possible with the telephone dialler.

A

[Phone banking, company menu options, postcode input]

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18
Q

What does the term ‘cadenced’ mean with regards to the telephone’s ring signal?

A

[It is the make-break ratio of the ring signal]

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19
Q

What is the cadence of the telephone’s ring signal voltage?

A

[0.4s on - 0.2s off - 0.4 on - 2s null - repeat cycle]

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20
Q

Why does music distort if transmitted over the voice telephone network?

A

[Frequencies below 300 Hz and above 3400 Hz are lost]

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21
Q

What term describes the ability of the human ear to compensate for large
differences in sound level?

A

[The ear’s dynamic range or non-linear response will also do]

22
Q

What is the name and nationality of the man who constructed and patented the first practical telephone?

A

[Alexander Graeme Bell; Canadian National, Scottish born

23
Q

List in chronological order the different voice switching technologies.

A

[Manual cord, step by step, crossbar, electronic control electromechanical (crossbar) switch, SPC fully electronic control and switch]

24
Q

What does the term MOSFET mean?

A

[Metal Oxide Semi-conductor, Field Effect Transistor]

25
Q

What is it about MOSFET devices that make them static discharge susceptible?

A

[Their physical construction incorporates a very thin oxide layer, this layer of insulation is susceptible to ESD destruction]

26
Q

Why is there a capacitor in series with the “bells” in a telephone?

A

[Blocks dc line current but passes ac ring current]

27
Q

What are the two main functions of the ‘hybrid’ circuit in a telephone?

A

converts between 2 and 4 wire circuits (line and phone); adjusts the level of sidetone to the correct amount]

28
Q

What is the function of the gravity switches (switch-hooks)?

A

[They switch between the bell and phone circuitry when on and off hook]

29
Q

Why is the level of Side Tone regulated in a telephone?

A

[So that speech is at the correct volume for the system’s transmission cequipment]

30
Q

How is the ac voice signal separated from the dc line current?

A

By either capacitor or transformer]

31
Q

Explain the basic operation of the telephone ringer circuit.

A

When the phone is on-hook the bells are connected to line. The capacitor blocks dc but passes ac ring current when the phone is called]

32
Q

Briefly describe the function of a PABX.

A

[It is a privately owned switching system (exchange) typically owned by companies to service their staff. All internal calls are free

33
Q

What does the term ‘Blocking’ refer to in telephony switching?

A

[When there are no free switching paths through the exchange equipment, the caller receives a congestion tone]

34
Q

What does the term ‘Common Control’ mean in telephony switching?

A

[The equipment that sets up the call is not linked to the call. Once the the call is set up the common equipment is used for another call etc]

35
Q

Why was Ericsson’s electromagnetic telephone switch referred to as Crossbar?

A

[Because of its physical construction of horizontal and vertical bars forming a 10 x 10 contact matrix]

36
Q

What event in history led to the invention of automatic voice switching?

A

[The story goes that the wife of Strowger’s business competitor was a manual switchboard operator and Strowger believed business was being directed away from him]

37
Q

Write a basic definition of TDM (Time Division Multiplexing).

A

[It is where several different calls are essentially segmented and samples of each call are transmitted (digitally) over the same circuit in series in different time slots]

38
Q

List six system features of CAE (PABX’s and Key Systems).

A
  • voice mail
  • call hold
  • call pick-up
  • call transfer
  • call waiting
  • conference call
39
Q

What does the “Night Switching” function on a PABX do?

A

[Night Switching allows for incoming calls to be dealt with outside the company’s normal business hours. This means that all calls can be fielded and so avoid loss of business.]

40
Q

What is the basic function of a PABX’s Call Accounting software/hardware?

A

[Captures, records and costs phone usage

41
Q

What does the ‘Conference Call’ facility allow?

A

[Allows more than two extensions to be connected to the one call, typically the circuit configuration is in blocks of three. So a conference call with 4 callers needs 2 conference circuits]

42
Q

Explain the difference between ‘Blind’ and ‘Consultation’ Call Transfer

A

BLIND: allows the transferring of a call to a busy extension

CONSULTATION: keying the transfer code places the caller on hold, then a new dial extension is made possible, when answered the original caller and the intend receiver can converse.

43
Q

Which system feature automatically routes incoming calls to another extension in a group if the dialled extension is busy or does not answer?

A

[Hunt group, either circular or terminating]

44
Q

1 Briefly describe Direct Inward Dialling (DID).

A

[Outside calls can be made directly to an extension if the extn number is known. The company prefix is dialed followed by the extn number.]

45
Q

What is the advantage of DID?

A

[The advantage of DID is that the caller avoids the need to go via a switchboard operator.]

46
Q

Describe one physical hazard and one chemical hazard which can cause damage to printed circuit-board assemblies.

A

[Physical – bending the board, Chemical – oils off fingers]

47
Q

What is the main difference between a Wireline and a VOIP telephone
Handset?

A

[Wireline – Analogue speech output to the exchange,then digitised;
VOIP – speech converted to Digital by the phone]

48
Q

Describe two packaging methods for protecting printed circuit-board assemblies and components from damage by static discharge.

A

[Anti-static bags, carbon impregnated foam]

49
Q

Why must we avoid flexing PCB’s (Printed Circuit Boards)?

A

[Can cause physical damage]

50
Q

List four considerations to reduce the possibility of static damage when working on electronic switching equipment (PABX’s).

A
  • isolate power from the CAE when removing or inserting PBAs
  • use anti-static floor mats
  • do not touch any component on a PBA as they are fragile
  • its important to protect PBAs containing memory from sunlight and UV light

TELECOMMUNICATION Reviews (2 decks)

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