FM Broadcast Standards Definition of Terms 1. FM Broadcast Band – that portion of the radio frequency spectrum from 88 MHz to 108 MHz. The band is divided into 100 channels. 2. FM Broadcast Channel – a band of frequencies 200 kHz wide and is designated by its center frequency. Channels for FM broadcast stations begin at 88.1 MHz and continue in successive steps of 200 kHz to and including 107.9 MHz. 3. FM Broadcast Station – a station employing frequency modulation in the FM broadcast band and intended to be received by the general public. 4. Frequency Modulation – a system of modulation where the instantaneous frequency varies in proportion to the instantaneous amplitude of the modulating signal, and the instantaneous radio frequency is independent of the frequency of the modulating signal. 5. Center Frequency – the carrier frequency allocated by the Authority. 6. Frequency Swing – the instantaneous departure of the frequency of the emitted wave from the center frequency resulting from modulation. 7. Antenna Height Above Average Terrain (HAAT) – (a) height of the radiation center of the antenna above the terrain 3 to 16 km from the antenna. Generally, a different antenna height will be determined for each radial direction from the antenna. The average of these various heights is considered as the antenna HAAT. (b) where circular or elliptical polarization is employed the antenna HAAT shall be based upon the height of the radiation center of the antenna which transmits the horizontal components of radiation. 8. Antenna Field Gain – the ratio of the effective free space field intensity produced at 1.6 km in the horizontal plane expressed in millivolts per meter for one kilowatt antenna input power, to 137.6 millivolts per meter. 9. Antenna Power Gain – the square of the ratio of the root-mean-square free space field strength produced at 1.6 km in the horizontal plane, in millivolts per meter for one kilowatt antenna power, to 137.6 millivolts per meter. This ratio should be expressed in dB. 10. Effective Radiated Power (ERP) – the product of the transmitter power (transmitter output power less transmission line loss) multiplied by
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(a) the antenna power gain or (b) the antenna field gain squared. Where circular or elliptical polarization is employed, the term “ERP” is applied separately to the horizontal and vertical components of radiation. Field Intensity – the electric field intensity in the horizontal direction. Free Space Field Intensity – the field intensity that would exist at a point, in the absence of waves reflected from the earth or other reflecting objects. Service Area – as applied to FM broadcasting, means the service resulting from an assigned effective radiated power and antenna height above average terrain. Radio Frequency (RF) Protection Ratio – the value of the RF wanted-to-interfering signal ratio that enables, under specified conditions, the radio-frequency protection ratio to be obtained at the output of a receiver. Percentage Modulation – the ratio of actual frequency swing to the frequency swing defined as 100% modulation, expressed in percentage. For FM broadcasting stations, a frequency swing of +/- 75 kHz is defined as 100% modulation. Multiplexing – implies that two or more independent sources of information are combined for carriage over a single medium, namely, the radio frequency “carrier”, and then are separated at the receiving end. In stereophonic broadcasting, for example, program information consisting of left and right audio signals are multiplexed onto an FM carrier for transmission to receivers which subsequently recover the original audio signals. FM Stereophonic Broadcast – the transmission of a stereophonic program by a single FM broadcast station utilizing the main channel and a stereophonic sub-channel. Channel – a transmission path. The distinction between the concept of a “Channel” and a “Signal” are not always clear. The usage herein distinguished between transmission channels; e.g. main channel, stereophonic subchannel, etc., and left and right audio “signals”. Composite Baseband Signal – a signal which is the sum of all signals which frequencymodulates the main carrier. The signal can be represented by a formula which includes all signal components: the main channel signal, the modulated stereophonic subcarrier, the pilot subcarrier and the SCA subcarrier(s).
20. FM Baseband – the frequency band from 0 Hz to a specified upper frequency which contains the composite baseband signal. 21. Main Channel – the band of frequencies from 50 (or less) Hz to 15,000 Hz on the FM baseband which contains the main channel signal. 22. Main Channel Signal – a specified combination of the monophonic or left and right audio signals which frequency-modulates the main carrier. 23. Stereophonic Sound – the audio information carried by plurality of channels arranged to afford the listener a sense of the spatial distribution of sound sources. Stereophonic sound includes, but is not limited to, biphonic (two channel), triphonic (three channel) and quadrophonic (four channel) services. 24. Stereophonic Sound Subcarrier – a subcarrier within the FM broadcast baseband used for transmitting signals for stereophonic sound reception of the main broadcast program service. 25. Stereophonic Sound Subchannel – the band of frequencies from 23 kHz to 99 kHz containing sound subcarriers and their associated sidebands. 26. Subchannel – a transmission path specified by a subchannel signal occupying a specified band of frequencies. 27. Subchannel Signal – subcarrier(s) and associated sideband(s) which frequencymodulate the main carrier. It is synonymous with “subcarrier”, as in the stereophonic subcarrier or SCA subcarrier. 28. Pilot Sub-carrier – a pilot sub-carrier serving as a control signal for use in the reception of FM stereophonic broadcast. 29. Left (or Right) Signal – the electrical output of a microphone or a combination of microphones placed so as to convey the intensity, time, and location of sounds originating predominantly to the listener’s left (or right) of the center of the performing area. 30. Left (or Right) Stereophonic Channel – the left (or right) signal as electrically reproduced in the reception of an FM stereophonic broadcast. 31. Stereophonic Separation – the ratio of the electrical signal caused in the right (or left) stereophonic channel, to the electrical signal caused in the left (or right) stereophonic channel, by the transmission of only a right (or left) signal.
32. Frequency Deviation – the peak difference between the instantaneous frequency of the modulated wave and the carrier frequency. 33. Injection Ratio – the ratio of the frequency swing of the FM carrier by a subchannel signal to the frequency swing defined as 100% modulation, expressed in percentage. The total injection of more than one subchannel signal is the arithmetic sum of each subchannel. 34. Crosstalk – an undesired signal occurring in one channel caused by an electrical signal in another channel. 35. Linear Crosstalk – a form of crosstalk in which the undesired signal(s) is created by phase or gain inequalities in another channel or channels. Such crosstalk may be due to causes external to the stereophonic generator; consequently it is sometimes referred to as “system crosstalk”. 36. Nonlinear Crosstalk – a form of crosstalk in which the undesired signal(s) is created by harmonic distortion or intermodulation of electrical signal(s) in another channel or channels. Such crosstalk may be due to distribution within the stereophonic generator or FM transmitter; consequently it is sometimes referred to as “transmitter crosstalk”. 37. SCA – acronym for “Subsidiary Communications Authorization.” 38. Index of Cooperation – as applied to facsimile broadcasting, is the product of the number of lines per inch, the available length in inches, and the reciprocal of the line-use ratio. 39. Line-use Ratio – as applied to facsimile broadcasting is the ratio of the available line to the total length of scanning line. 40. Available Line – means the portion of the total length of scanning line that can be used specifically for picture signals. 41. Rectilinear Scanning – the process of scanning an area in a predetermined sequence of narrow straight parallel strips. 42. Optical Density – the logarithm (to the base 10) of the ratio of incident to transmitted or reflected light. 43. Experimental Period – the period between 12 midnight to 5:00 a.m. local standard time (1600 – 2100 GMT). This period may be used for experimental purposes in testing and maintaining apparatus by the licensee of any FM broadcast station on its assigned frequency and not in excess of its authorized power, provided no interference is caused to other
stations maintaining a regular schedule within such period.
operating
44. Operating Power – the product of the plate voltage (Ep) and the plate current (Ip) of the last radio stage and efficiency factor, F, expressed: Operating Power = EP x Ip x F. This is the indirect method of determining the operating power of each FM station for the purpose of specifying the operating power range of FM transmitters. The factor F shall be established by the transmitter manufacturer for each type of transmitter and shall be specified in the instruction book(s) supplied to each customer with each transmitter. 45. Last Radio Stage – the oscillator or radiofrequency power amplifier stage which supplies power to the antenna. 46. Qualified Technician – a person who is a holder of any class of Radio Telephone Operator’s License or its equivalent except those mentioned in Section 7.4 as issued by the existing regulatory body. Classes of FM Broadcast Stations 1. Class A – shall have an authorized transmitter power not exceeding 25 kW and an effective radiated power (ERP) not exceeding 125 kW and limited in antenna height of 2,000 feet above average terrain. The minimum transmitter power shall be 10 kW. Class A stations shall only be allowed in Metro Manila and Metro Cebu. 2. Class B – shall have an authorized transmitter power not exceeding 10 kW and an effective radiated power not exceeding 30 kW, and limited in antenna height of 500 feet above average terrain. The minimum transmitter power shall be 1 kW. 3. Class C – non-commercial, community station having an authorized radiated power not exceeding 1 kW (ERP). 4. Class D – shall have an authorized transmitter power not exceeding 10 watts. Educational stations shall be allowed to operate with Class D transmitter power. All classes of FM stations shall be protected to the 1mV/m contour or 60 dBu contour.
Radio-Frequency Protection Ratios The following radio frequency protection ratios provide for the minimum physical separation between stations and protection of stations from interference. RADIO-FREQUENCY PROTECTION RATIOS (dB) (based on the horizontal component of radiation) Frequency Spacing (kHz) 0 200 400
RF Signal Ratio 60 dBu : 15 dBu 60 dBu : 53 dBu 60 dBu: 80 dBu
Intermediate frequency amplifiers of most FM broadcast receivers are designed to operate on 10.7 MHz. For this reason the assignment of two stations in the same area one with a frequency of 10.6 or 10.8 MHz removed from that of the other, should be avoided if possible. FM Broadcast Stations, shall not be authorized to operate in the same city or in nearby cities with a frequency separation of less than 800 kHz. The nature and extent of the protection from interference accorded the FM broadcast stations is limited solely to that which results from the application of the radio frequency protection ratio. A commercial broadcast entity may establish only one primary FM radio station within the geographical boundaries of any province. Technical Requirements 1. Safety Requirements Conformity with Electrical Wiring Rules – all equipment using electrical power shall conform with the provisions of the Philippine Electrical Code and the Philippines Electronics Code so as to ensure the safety of property, equipment, personnel and the public in general. All component parts shall be in accordance with generally accepted standards or those of the International Standards.
2. Transmitting Facilities a. Location and Layout – any site particularly suitable for FM broadcasting in an area, in the absence of other comparable sites, may be shared by and be made available to as many applicants as possible. The transmitting site should be selected consistent with the purpose of the station, i.e., whether it is intended to serve a small city, a metropolitan area, or a large region. The location should be so chosen that line-of-sight can be obtained from the antenna over the principal city or cities to be served.
a. Electrical Performance Standards – the general design of the FM broadcast transmitting system (from input terminal of microphone preamplifier, through audio facilities at the studio through lines or other circuits between studio and transmitter, through audio facilities at the transmitter, and through the transmitter, but excluding equalizers for the correction of deficiencies in microphone response) shall be in accordance with the following principles and specifications: i.
The transmitter shall operate satisfactorily in the operating power range with a frequency swing of +/- 75 kHz, which is defined as 100% modulation.
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The transmitting system shall be capable of transmitting a brand of frequencies from 50 to 15,000 Hz. Pre-emphasis shall be employed in accordance with the impedance-frequency characteristics of a series inductance-resistance network having a time constant of 75 microseconds. The deviation of the system response from the standard pre-emphasis curve shall lie between two limits. The upper of these limits shall be uniform: (no deviation) from 50 to 15,000 Hz. The lower limit shall be uniform from 100 to 7,500 Hz and 3 dB below the upper limit; from 50 to 100 Hz and the lower limit shall fall from the 3 dB limit at a uniform rate of 1 dB per octave (4 dB at 50 Hz); from 7,500 to 15,000 Hz, the lower limit shall fall from the 3 dB limit at a uniform rate of 2 dB per octave (5 dB at 15,000 Hz).
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At any modulating frequency between 50 and 15,000 Hz and at modulation percentages of 25, 50, and 100 percent, the combined audio frequency
b. Antenna System – it shall be standard to employ horizontal polarization. However, circular or elliptical polarization of the clockwise or counterclockwise rotation may be employed, if so desired. The antenna must be constructed such that it is clear of surrounding buildings or objects that would cause shadow problems. In the event a common tower is used by two or more licensees for antenna and/or antenna supporting purposes, the licensee who owns the tower shall assume full responsibility for the maintenance of the tower structure, its painting and lighting requirements. In case of shared ownership, only one licensee shall assume such responsibility. For the protection of air navigation, the antenna and supporting structure shall be painted and illuminated in accordance with ATO regulations. 3. Transmitter and Associated Equipment
harmonics measured in the output of the system shall not exceed the root-mean-square values given in the following Modulating Frequency 50 to 100 Hz 100 to 7,500 Hz 7,500 to 15,000 Hz table:
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The transmitting system output noise level (amplitude modulation) in the band of 50 to 15,000 Hz shall be at least 50 dB below the level representing 100% amplitude modulation. The noise-measuring equipment shall be provided with a standard 75microsecond de-emphasis; and the ballistic characteristic of the instrument shall be similar to those of the standard VU meter.
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Automatic means shall be provided in the transmitter to maintain the assigned center frequency within the allowable tolerance of (+/- 2000 Hz).
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The transmitter shall be equipped with suitable indicating instruments for the determination of operating power and with other instruments as are necessary for proper adjustments, operation, and maintenance of the equipment.
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Adequate provision shall be made for varying the transmitter output power to compensate for excessive variations in line voltage or for other factors affecting the output power.
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Allowances shall be provided in all component parts to avoid overheating at the rated maximum output power.
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If a limiting or compression amplifier is employed, precaution should be maintained in its connection in the circuit due to the use of pre-emphasis in the transmitting system.
Distortion 3.5% 2.5% 3%
Measurements shall be made employing a 75-microsecond de-emphasis in the measuring equipment and 75-microsecond pre-emphasis in the transmitting equipment, and without compression, if a compression amplifier is employed. Harmonics shall be included to 30,000 Hz. It is recommended that none of the three main divisions of the system (transmitter, studio to transmitter circuit, and audio facilities) contribute over onehalf of these percentages since at some frequencies the total distortion may become the arithmetic sum of the distortion of the divisions. The transmitting system output noise level (frequency modulation) in the band of 50 to 15,000 Hz shall be at least 60 dB below 100% modulation (frequency swing of +/- 75 kHz). The measurement shall be made using 400 Hz modulation as a reference. The noise measuring equipment shall be provided with a standard 75microsecond de-emphasis; the ballistic characteristic of the instrument shall be similar to those of the standard VU meter.
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Any emission appearing on a frequency removed from the carrier by between 120 kHz, and 240 kHz, inclusive, shall be attenuated at least 25 dB below the level of the unmodulated carrier. Any emission appearing on a frequency removed from the carrier by more than 240 kHz and up to and including 600 kHz shall be attenuated at least 35 dB below the level of the unmodulated carrier. Any emission appearing on a frequency removed from the carrier by more than 600 kHz shall be attenuated at least 43 + 10 Log10 (Power, in watts) dB below the level of the unmodulated carrier, or 80 dB, whichever is the lesser attenuation.
disconnect all voltages in excess of 350 volts when any access door is opened. ii.
Means shall be provided for making all tuning adjustment, requiring voltages in excess of 350 volts to be applied to the circuit, from the front of the panels with all access doors closed.
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Proper bleeder resistors or other automatic means shall be installed across all capacitor banks to lower any voltage which may remain accessible with access door open to less than 350 volts within 2 seconds after the access door is opened.
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All plate supply and other high voltage equipment, including transformers, filters, rectifiers and motor generators, shall be protected so as to prevent injury to operating personnel.
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Power equipment and control panels of the transmitter shall meet the above requirements. Exposed 220 volts AC switching equipment on the front of the power control panels is not recommended.
Construction
In general, the transmitter shall be constructed either on racks and panels or in totally enclosed frames protected as required by the Philippine Electronics Code and the Philippine Electrical Code and those set forth below: c. a) Enclosure – the transmitter shall be enclosed in a metal frame or grille, or separated from the operating space by a barrier or other equivalent means. All metallic parts shall be connected to ground. b) Grounding of Controls – all external metallic handles and controls accessible to the operating personnel shall be effectively grounded. No circuit in excess of 100 volts shall have any part exposed to direct contact. A complete dead front type of switchboard is preferred. c) Interlocks on Doors – i.
All access doors shall be provided with interlocks which will
Wiring and Shielding i.
The transmitter panels or units shall be wired in accordance with standard switchboard practice, either with insulated leads properly cabled and supported or with rigid bus bar properly insulated and protected.
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Wiring between units of the transmitter, with the exception of circuits carrying RF energy, shall be installed in conduits or approved fiber or metal raceways for protection from mechanical injury.
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Circuits carrying RF energy between units shall be coaxial, or two-wire balanced lines, or properly shielded.
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All stages or units shall be adequately shielded and filtered to prevent interaction and radiation.
circuits carrying high potential radio frequency energy. e. Indicating Instruments i.
Each FM broadcast station shall be equipped with indicating instruments for measuring the direct plate voltage and current of the last radio stage and the transmission line radio frequency power. In the event that the plate voltmeter or plate ammeter in the last radio stage is defective, the operating power shall be maintained by means of the RF power meter.
d. Metering Equipment ii. i.
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All instruments having more than 1,000 volts potential to ground on the movements shall be protected by a cage or cover. (some instruments are designed by the manufacturer to operate safely with voltages in excess of 1,000 volts on the movement). In case the plate voltmeter is located on the low potential side of the multiplier resistor with the potential of the high potential terminal to the instrument at or less than 1,000 volts above ground, no protective case is required. However, it is good practice to protect voltmeters subject to more than 5,000 volts with suitable over-voltage protective device(s) across the instrument terminal in case the winding opens.
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Installation i.
The installation shall be made in suitable quarters. Since an operator must be on duty at the transmitter control during operation, suitable facilities for his welfare and comfort shall be provided at the control point.
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g. Other technical data An accurate circuit diagram, as furnished by the manufacturer of the equipment, shall be retained at the transmitter location. 4. Monitoring Equipment a. Frequency Monitor i.
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Transmission line meters and any other radiofrequency instrument which may be necessary for the operator to read, shall be so installed as to be easily and accurately read without the operator having to risk contact with
The licensee of each station shall have in operation, either at the transmitter or at the place where the transmitter is controlled, a frequency monitor of a type approved by the Commission which shall be independent of the frequency control of the transmitter.
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In the event that the frequency monitor becomes defective, the station may be operated without such equipment pendings its repair or replacement for a period not in excess of 60 days without further authority of the Commission: Provided, that: a) Appropriate entries shall be made in the operation log of the station to show the date and time the monitor was removed from and restored to service. b) The engineer in charge of the region in which the station is located shall be notified both immediately after the monitor is found to be defective and immediately after the repaired or replacement monitor has been installed and is functioning properly. c) The frequency of the station shall be compared with an external frequency source of known accuracy at sufficiently frequent intervals to insure that the frequency is maintained within the tolerance. An entry shall be made in the station log as to the method used and the results thereof.
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If conditions beyond the control of the licensee or permittee prevent the restoration of the monitor to service within the above allowed period, informal request may be filed with the engineer in charge of the region
in which the station is located for such additional time as may be required to complete repairs of the defective instrument or equipment.
