ece elective iii

ECE ELECTIVE III

BROADCAST ENGINEERING AND ACOUSTICS

Course Content Introduction to AM Broadcasting System and

Standards Introduction to FM Broadcasting System and

Standards Introduction to TV Broadcasting System and

Standards Introduction to Engineering Acoustics Room Acoustics Speaker Systems, Speaker Enclosures and

Microphones Crossover and Dividing Networks

ECE ELECTIVE IIIBROADCAST ENGINEERING AND ACOUSTICS

ECE ELECTIVE III


Introduction to AM Broadcasting System

and Standards

BroadcastingBroadcasting is the distribution of

audio and/or video signals (programs) to a number of recipients ("listeners" or "viewers") that belong to a large group.

Broadcasting to a very narrow range of audience is called narrowcasting.


Broadcasting The term "broadcast" was coined by early

radio engineers from the midwestern United States. "Broadcasting", in farming, is one method of spreading seed using a wide toss of the hand, in a broad cast.

Television and radio programs are distributed through radio broadcasting or cable, often both simultaneously.

Broadcasting forms a very large segment of mass media.


Amplitude Modulation (AM)The process of varying the

amplitude of a high-frequency carrier wave in accordance with the amplitude of the modulating signal.


EM Spectrum Properties


Uses of AM1. Broadcasting Long wave AM Radio 148.5 – 283.5 kHz

(LF) Medium wave AM Radio 530 kHz – 1710 kHz (MF) International Shortwave AM Radio 3 MHz – 30 MHz

(HF)

2. Citizen’s Band Radio (27 MHz)

3. Aircraft communications (108 – 136 MHz) 4. TV picture (using vestigial sideband)


http://en.wikipedia.org/wiki/Longwave

http://en.wikipedia.org/wiki/Longwave

http://en.wikipedia.org/wiki/Medium_wave

http://en.wikipedia.org/wiki/Medium_wave

http://en.wikipedia.org/wiki/Shortwave_bands

http://en.wikipedia.org/wiki/Shortwave_bands

Limiting condition for AM:

The amplitude of the modulating signal must not exceed that of the carrier, else overmodulation (clipping) occurs.


AM Broadcasting Standards (FCC) Frequency allocation: 535 to 1605 kHz (525 to

1705 kHz) divided into 106 (130) channels Channel spacing: 10 kHz (9 kHz) Permitted channel bandwidth: 30 kHz

(maximum modulating signal frequency: 15 kHz)*note: geographically co-located stations must be spaced at least 3 channels apart for sideband interference protection)

Carrier tolerance: ± 20 Hz Unmodulated carrier power: 100 W to 50 kW Type of emission: A3E (double sideband, full

carrier) Intermediate Frequency: 455 kHz


AM Broadcasting Standards (KBP) Frequency allocation: 526.5 to 1705 kHz

Start of carrier frequency: 531 kHz

Channel spacing: 9 kHz


AM Station PerformanceRequirements (FCC) Modulation percentage: 85% to 95% Audio frequency distortion

harmonics (AFDH): <5% rms amplitude up to 84% modulation

Audio frequency response: transmission characteristic must be flat from 100 Hz to 5 kHz (± 2 dB referred to 1 kHz)

Carrier stability: ± 20 Hz


Service Areas in AMPrimary Area in which the ground wave field is measured at 1

mV/m, and is not subject to objectionable interference and fading

Secondary The area serviced by the sky wave, having a sky wave

field strength equal to or greater than 500 μV/m for 50% or more of the time. May be subject to fading but no objectionable co-channel interference

Intermittent The area receiving service from the ground wave but

beyond the primary service area and subject to objectionable interference and fading


Times of Day in AM BroadcastingDaytime From local sunrise to local sunset 6 AM to 6 PM (2200 UTC to 1000 UTC)

Nighttime Between local sunset to local sunrise 6 PM to 6 AM (1000 UTC to 2200 UTC) Experimental period Midnight to local sunrise 12 MN to 6 AM (1600 UTC to 2200 UTC) Used for experimental purposes in testing and maintaining

apparatuses by the licensee, provided that no interference is caused to other stations maintaining a regular operating schedule within such a period


3 Important Requirements in Broadcasting1. Timing Programming schedule must be followed

(programs should start and end within the allotted time)

2. Fidelity Program material shall not have any reasonable

distortion3. Modulation depth The audio signal must modulate the transmitter

properly


Power AllocationsAREA Maximum Permissible

Power

Metro Manila 50 kW

All other areas 10 kW


The transmitter of existing Metro Manila stations may be located outside of Metro Manila, provided that Metro Manila remains within the 80 dBu contour of the transmitter. The station shall not operate more than 5% and lower than 10% of its authorized operating power.

Classification of Powers1. Licensed power or authorized operating power That which is actually supplied or fed to the antenna by the

transmitter. Should have a tolerance of -5% or +10%

2. Maximum rated carrier power The maximum power that the transmitter is capable of

supplying to the antenna and still operate satisfactorily

3. Plate input power Product of the voltage and current at the output of the last

radio stage, measured without modulation 4. Antenna input power Product of the square of the antenna current and the

antenna resistance at the point where the current is measured.


Two methods of measuring antenna input power1. Direct method


Where: Ia = antenna current w/ no modulationRa = impedance or resistance of the antenna where the current is measured2. Indirect method

• used to determine the output power of FM broadcast stations and TV aural transmitters

• used for AM broadcast stations in emergencies

Where:Vp = plate voltage of the final amplifierIp = plate current of the final amplifierF = power factor correction

AM Antennas and Site Considerations Standard AM broadcast stations use either a single

omnidirectional vertical antennas, or multi-element, phased vertical directional arrays

Generally, antennas are erected on flat lands, preferably those having good ground conductivities (e.g. marsh lands)

Earth mat – a network of buried wires directly under the antenna, extending outward from the base, buried about 6 to 12 inches (15 to 30 cm) below the ground

Counterpoise – a smaller version of the earth mat above ground


Antenna Towers:Obstruction Painting and Lighting

Must be painted with equal-width stripes of aviation (emergency) orange and white, each stripe approximately one-seventh of the height of the tower, but not over 100 ft (30 m) in width on tall towers. The top and bottom stripes must be orange



To mark the tower at night (sunset to sunrise), towers up to 150 ft (46 m) must have two (2) steady-burning 116-W or 125-W lamps in an aviation red light globe at the top of the tower (beacon)

For towers over 150 ft, the top beacon light consists of 620-W or 700-W PS-40 Flashing Code Beacon lamps with aviation red filters



At half-, third-, quarter-, etc. tower height points (depending on the height of the tower), flashing 620-W to 700-W beacons are installed

Lights should be automatically controlled by a device sensitive to the night sky.

Lights should be inspected at least once a day, or by automatic indicators


Broadcast Auxiliary ServicesA broadcast auxiliary service or BAS is any radio frequency system used by a radio station or TV station, which is not part of its direct broadcast to listeners or viewers. These are essentially internal-use backhaul channels not intended for actual reception by the public, but part of the airchain required to get those signals to such a transmitter.


STUDIO-TO-TRANSMITTER LINK/REMOTE CONTROL SYTEM

The frequency band allocation for STUDIO-TO-TRANSMITTER LINK/REMOTE CONTROL SYTEM shall be: Band A 300-315 MHz Band B 734-752 MHz Band C 942-952 MHz The maximum power allowable for STL's

shall be 15 watts.


REMOTE PICK-UP STATION

The frequency band allocation for REMOTE PICK-UP STATION shall be: Band A 315-325 MHz Band B 450-451 MHz Band C 455-456 MHz The maximum power allowable for

Remote Pick-up Stations shall be 35 watts.


COMMUNICATIONS, COORDINATION AND CONTROL LINK

The frequency band allocation for COMMUNICATIONS, COORDINATION AND CONTROL LINK shall be: Band A 412 MHz (non-exclusive) Band B 25.67 - 26.1 MHz Band C 162.235 - 162.615 MHz

166.250 - 170.150 MHz Band D 432.5 - 433 MHz

437.5 - 438 MHz


COMMUNICATIONS, COORDINATION AND CONTROL LINK

The maximum power allowable for Communications, Coordination and Control Link shall be:

Band A - 100 watts (SBS)B - 160 watts (ERP)C - 160 watts (ERP)D - 200 watts (for repeater)


OPERATING REQUIREMENTS: Hours of Operation

Minimum Operating Schedule The licensee of each medium-frequency

broadcast station shall maintain a minimum operating schedule of two-thirds of the total hours that it is authorized to operate except that in emergencies when, due to causes beyond the control of the licensee, it becomes impossible to continue operating, the station may cease operations for a period not exceeding 10 days.


OPERATING REQUIREMENTS: Hours of OperationMinimum Operating Schedule Broadcast(s) outside of the authorized regular

operating schedules (as before regular sign-on schedules and/or beyond the regular sign-off schedules) may be aired without prior authorization from the Authority provided the program falls under an emergency category or of very important relevance to the station's existence. The information shall be entered in the program and operating logs at the time the broadcast was aired.


OPERATING REQUIREMENTS: Hours of Operation

Minimum Operating Schedule If a permanent discontinuance of

operations is being contemplated, then the licensee shall notify in writing the Authority or regional office where the station is located at least two (2) days before the actual discontinuance is effected.


Station identification Announcements A licensee of a medium-frequency

broadcast station shall make station identification announcements (call letters, frequency, and location) at the beginning and ending of each time of operation and during operation on the hour and either on the half hour or at the quarter hour preceding the next hour:


Station identification Announcements Such identification announcement need not

be made on the half hour or quarter hour when, to make such announcement, would interrupt a single consecutive speech, play, religious service, symphony concert, or operatic production. In such cases, an identification announcement shall be made at the first interruption of the entertainment continuity and at the conclusion of. the program:


Station identification Announcements Provided, that an announcement within five

minutes of either on the half hour or at the quarter hour preceding the next hour will satisfy the requirements of identification announcements. In the case of variety show programs, basketball game broadcasts, or similar programs of longer duration than 30 minutes, the identification announcement shall be made within 5 minutes of the times specified in the hours of operation.


Logs

Log A listing of the date and time of events,

programs, equipment parameters, tests, malfunctions, corrections, and other such information


Types of Logs in Broadcast OperationsProgram Log Contains entries with regard to the nature of the program,

its name and title, start and end times, source, sponsors of announcements, duration of advertisements, etc.

Operating Log Contains the technical details of the transmitter during

operation, such as operating parameters (Vp, Ip, Ia, etc.), the time the transmitter is put on and off the air, the time antenna lights are turned on or off, etc.

Maintenance Log Contains the results of transmitter and other equipment

tests, repairs, calibration, checks, etc.


AM STEREOPHONIC STANDARD The AM stereophonic standard is the C-

QUAM (Compatible Quadrature Amplitude Modulation) AM stereophonic system.

Stereophonic AM broadcasting involves the transmission of additional information with the monophonic signal on the AM carrier allowing the reception of the original monophonic signal and left and right stereophonic signals.


AM STEREOPHONIC STANDARD The stereophonic audio information is composed

of two signals; left (L) and right (R). As in the present AM broadcast standards, the carrier is amplitude modulated by the sum (L+R) signal. The additional information in the form of the difference (L-R) signal is added to the carrier by quadrature phase modulation. A separate pilot signal is added to the difference signal to indicate the presence of a stereophonic broadcast.

C-QUAM is a registered trademark of Motorola Inc.


PUBLIC INFORMATION FILEPublic Information File shall contain the following: A copy of the station license. Documents as to mode of ownership including

trade name as registered in the Department of Trade.

A list of changes in transmitting facilities (arranged chronologically). Annex to this list, the corresponding licenses and permits supporting the changes.

Copies of the Program Standards, the Technical Standards, the NTC compilation of laws, regulations, circulars and memoranda.

Evidence of membership in the KBP.


ECE ELECTIVE III


Introduction to FM Broadcasting System

and Standards

Frequency Modulation (FM)Frequency Modulation The process of varying the frequency of a

high-frequency carrier wave in accordance with the amplitude variations of the modulating signal.


Uses of FM

1. FM broadcast (88 – 108 MHz)

2. Television sound

3. Satellite Television (both audio and video)

4. Mobile radio services


FM Broadcasting Standards (FCC)Frequency allocation: 88 to 108 MHz divided into 100 channelsChannel spacing: 200 kHzPermitted channel bandwidth: 200 kHz (±75 kHz deviation for maximum modulating frequency of 15 kHz, and a 25 kHz guard band on both sides)Type of emission: F3E (monoaural) F8E (stereophonic)Intermediate Frequency: 10.7 MHz (10.61 to 10.79 MHz)Pilot Subcarrier Frequency: 19 kHz


Classes of FM StationsClass-A Shall have an authorized transmitter power not

exceeding 25 kW and an ERP not exceeding 125 kW. Minimum transmitter power is 10 kW

Class-B Shall have an authorized transmitter power not

exceeding 10 kW and an ERP not exceeding 30 kW. Minimum transmitter power is 1 kW


Classes of FM Stations

Class-C A non-commercial, community station having an ERP

not exceeding 1 kW Class-D Shall have an authorized transmitter power not

exceeding 10 W. Used for educational purposes.


FM Antennas and Site Considerations The antenna used in FM broadcasting is

a half-wave dipole.

The transmitting antenna location should be chosen so that line-of-sight can be obtained from the antenna over the general service area.


FM Antennas and Site Considerations To provide LOS within the principal area,

the antenna must be conveniently above the average terrain.

A tower, elevated structures (buildings) can be used to elevate the antenna

Hills and mountains can also act as natural towers.


Pre-emphasis and De-emphasis Since noise sideband power in FM decreases

inversely with the modulating frequency, higher modulating frequencies are more susceptible to noise than the lower ones.

A method of artificially boosting the affected frequencies with respect to a pre-arranged curve before transmission to improve noise immunity is termed as pre-emphasis.


Pre-emphasis and De-emphasis The compensation at receiver side is

called de-emphasis

The amount of pre/de-emphasis for FM broadcasting has been standardized as 75μs

In the UK, the amount of emphasis is standardized to 50μs


Stereophonic FMStereo (also stereoscope)

Originally referred to a special photographic technique used to give the viewer the impression of observing a scene in three dimensions

In stereophonic audio, a sound source is recorded

from two different angles (in this case, the left and right sides). During playback, these signals simulate the sound to the left and right ears, giving the illusion of a three-dimensional sound source.


Problems encountered with initial design ofstereophonic FM broadcasts:

1. Original FM broadcasts were monophonic. The system should be compatible with existing monophonic receivers

2. The stereo information had to be transmitted within the 200 kHz bandwidth allotment


Block Diagram of a Stereophonic Transmission System


Spectrum of a Stereo FM Multiplex System


Some notes on FM Stereo

1. Why are the L & R signals not sent independently and simultaneously? So that the system will be compatible with existing

monoaural receivers 2. What’s the use of the 38 kHz subcarrier? To serve as the carrier for the balance modulation

process of the difference signal

3. Why 38 kHz? The difference signal must not interfere with the

original sum signals


Some notes on FM Stereo4. Why suppress the 38 kHz subcarrier? Too much of the total composite modulating signal would

be taken up by the subcarrier voltage

5. What’s with the 19 kHz pilot subcarrier? It is used as the reference to obtain the difference signal. 6. Why 19 kHz? Most people cannot hear beyond 15 kHz, much more 19

kHz.


Subsidiary Communications Authorization (SCA)

The transmission of programs which are

of a broadcast nature, but which are of interest primarily to limited segments of the public wishing to subscribe thereto.

Uses a subcarrier of 67 kHz and is modulated to a depth of 7.5 kHz


Typical applications of SCA1. Background music, weather, time signals2. Educational information3. Talk-back for remote stations4. Telemetry5. Facsimile6. Slow-scan TV


The Broadcast Studio The studio usually contains equipment

for program origination.

It is a usual practice to co-locate the studio and transmitter in a single facility, mostly for economic purposes.


Remote Studio Facilities In cases where the studio and the

transmitter cannot be located in the same facility, or it is better for the transmitter to be located elsewhere (economically or technically), then a studio-to-transmitter link (STL) may be employed.


ece elective iii

Documents

radio broadcasting

khz channel

tv broadcasting system

khz lfmedium wave

fm broadcasting system

khz mfinternational

carrier frequency

radio programs