View all text of Subpart G [§ 74.701 - § 74.799]
§ 74.750 - Transmission system facilities.
(a) A low power TV, TV translator, or TV booster station shall operate with a transmitter that is either certificated for licensing under the provisions of this subpart or type notified for use under part 73 of this chapter.
(b) Transmitting antennas, antennas used to receive the signals to be rebroadcast, and transmission lines are not certificated by the FCC. External preamplifiers also may be used provided that they do not cause improper operation of the transmitting equipment, and use of such preamplifiers is not necessary to meet the provisions of paragraph (c) of this section.
(c) The following requirements must be met before low power TV and TV translator transmitters will be certificated by the FCC:
(1) The equipment shall be so designed that the electrical characteristics of a standard television signal introduced into the input terminals will be maintained at the output. The overall response of the apparatus within its assigned channel, when operating at its rated power output and measured at the output terminals, shall provide a smooth curve, varying within limits separated by no more than 4 dB: Provided, however, That means may be provided to reduce the amplitude of the aural carrier below those limits, if necessary to prevent intermodulation which would mar the quality of the retransmitted picture or result in emissions outside of the assigned channel.
(2) Radio frequency harmonics of the visual and aural carriers, measured at the output terminals of the transmitter, shall be attenuated no less than 60 dB below the peak visual output power within the assigned channel. All other emissions appearing on frequencies more than 3 megacycles above or below the upper and lower edges, respectively, of the assigned channel shall be attenuated no less than:
(i) 30 dB for transmitters rated at no more than 1 watt power output.
(ii) 50 dB for transmitters rated at more than 1 watt power output.
(iii) 60 dB for transmitters rated at more than 100 watts power output.
(3) When subjected to variations in ambient temperature between minus 30 degrees and plus 50 degrees Centigrade and variations in power main voltage between 85 percent and 115 percent of rated power supply voltage, the local oscillator frequency stability shall maintain the operating frequency within:
(i) 0.02 percent of its rated frequency for transmitters rated at no more than 100 watts peak visual power.
(ii) 0.002 percent of the rated frequency for transmitters rated at more than 100 watts peak visual power.
(iii) Plus or minus 1 kHz of its rated frequency for transmitters to be used at stations employing offset carrier frequency operation.
(4) The apparatus shall contain automatic circuits which will maintain the peak visual power output constant within 2 dB when the strength of the input signal is varied over a range of 30 dB and which will not permit the peak visual power output to exceed the maximum rated power output under any condition. If a manual adjustment is provided to compensate for different average signal strengths, provision shall be made for determining the proper setting for the control, and if improper adjustment of the control could result in improper operation, a label shall be affixed at the adjustment control bearing a suitable warning.
(5) The apparatus must be equipped with automatic controls that will place it in a non-radiating condition when no signal is being received on the input channel, either due to absence of a transmitted signal or failure of the receiving portion of the facilities used for rebroadcasting the signal of another station. The automatic control may include a time delay feature to prevent interruptions caused by fading or other momentary failures of the incoming signal.
(6) The tube or tubes employed in the final radio frequency amplifier shall be of the appropriate power rating to provide the rated power output of the translator. The normal operating constants for operation at the rated power output shall be specified. The apparatus shall be equipped with suitable meters or meter jacks so that appropriate voltage and current measurements may be made while the apparatus is in operation.
(7) The transmitters of over 0.001 kW peak visual power (0.002 kW when circularly polarized antennas are used) shall be equipped with an automatic keying device that will transmit the call sign of the station, in International Morse Code, at least once each hour during the time the station is in operation when operating in the translator mode retransmitting the programming of a TV broadcast station. However, the identification by Morse Code is not required if the licensee of the low power TV or TV translator station has an agreement with the TV broadcast station being rebroadcast to transmit aurally or visually the low power TV or TV translator station call as provided for in § 74.783. Transmission of the call sign can be accomplished by:
(i) Frequency shift keying; the aural and visual carrier shift shall not be less than 5 kHz or greater than 25 kHz.
(ii) Amplitude modulation of the aural carrier of at least 30% modulation. The audio frequency tone used shall not be within 200 hertz of the Emergency Broadcast System Attention Signal alerting frequencies.
(8) Wiring, shielding, and construction shall be in accordance with accepted principles of good engineering practice.
(d) Low power TV, TV translator and transmitting equipment using a modulation process for either program origination or rebroadcasting TV booster transmitting equipment using a modulation process must meet the following requirements:
(1) The equipment shall meet the requirements of paragraphs (a)(1) and (b)(3) of § 73.687.
(2) The stability of the equipment shall be sufficient to maintain the operating frequency of the aural carrier to 4.5 MHz ±1kHz above the visual carrier when subjected to variations in ambient temperature between 30° and + 50° centigrade and variations in power main voltage between 85 and 115 percent of rated power supply voltage.
(e) Certification will be granted only upon a satisfactory showing that the apparatus is capable of meeting the requirements of paragraphs (c) and (d) of this section. The following procedures shall apply:
(1) Any manufacturer of apparatus intended for use at low power TV, TV translator, or TV booster stations may request certification by following the procedures set forth in part 2, subpart J, of this chapter.
(2) Low power TV, TV translator, and TV booster transmitting apparatus that has been certificated by the FCC will normally be authorized without additional measurements from the applicant or licensee.
(3) Applications for certification of modulators to be used with existing certificated TV translator apparatus must include the specifications electrical and mechanical interconnecting requirements for the apparatus with which it is designed to be used.
(4) Other rules concerning certification, including information regarding withdrawal of type acceptance, modification of certificated equipment and limitations on the findings upon which certification is based, are set forth in part 2, subpart J, of this chapter.
(f) The transmitting antenna system may be designed to produce horizontal, vertical, or circular polarization.
(g) Low power TV, TV translator, or TV booster stations installing new certificated transmitting apparatus incorporating modulating equipment need not make equipment performance measurements and shall so indicate on the station license application. Stations adding new or replacing modulating equipment in existing low power TV, TV translator, or TV booster station transmitting apparatus must have a qualified person examine the transmitting system after installation. This person must certify in the application for the station license that the transmitting equipment meets the requirements of paragraph (d)(1) of this section. A report of the methods, measurements, and results must be kept in the station records. However, stations installing modulating equipment solely for the limited local origination of signals permitted by § 74.731 need not comply with the requirements of this paragraph.