rent shall be measured by an ammeter of accepted accuracy. These data must be submitted to and approved by the Commission before any licensee will be authorized to operate by this method of power determination. The antenna ammeter shall not be changed to one of different type, maximum reading or accuracy without the authority of the Commission. If any change is made in the antenna system or any change made which may affect the antenna system, the method of determining operating power shall be changed immediately to the indirect method. [Rule 137] 3.97 Radiated power. The operating power of a broadcast station determined by the radiated power computed from field intensity measurements may be accepted in lieu of antenna input power, provided a sufficient number of measurements are taken to insure accuracy and an analysis of the antenna system is submitted indicating the relative distribution of the radiation (i.e., ground and sky wave radiation). The data on the antenna resistance, complete description of the antenna system with dimensions and method of taking field intensity measurements and of relating these measurements to the operating power shall be submitted to and approved by the Commission before any license will be authorized to operate by this method of power determination. If any change is made in the antenna system or any change made which may affect the antenna system, the method of determining operating power shall be changed immediately to the indirect method.*+ [Rule 138] 3.98 Modulation requirements. (a) A licensee of a broadcast station will not be authorized to operate a transmitter unless it is capable of delivering satisfactorily the authorized power with a modulation of at least 85 percent. When the transmitter is operated with 85 percent modulation, not over 10 percent combined audio frequency harmonics shall be generated by the transmitter. (b) All broadcast stations shall, on and after November 1, 1936, have in operation a modulation monitor approved by the Commission.17 (c) The operating percentage of modulation of all stations shall be maintained as high as possible consistent with good quality of transmission and good broadcast practice and in no case less than 85 percent on peaks of frequent recurrence during any selection which normally is transmitted at the highest level of the program under consideration. (d) The Commission will, from time to time, publish the specifications, requirements for approval, and a list of approved modulation 17 The following modulation monitors have been approved by the Commission: *For statutory and source citations, see note to § 3.1. Page 143 monitors.18 (Secs. 4 (i), 303 (e), 48 Stat. 1068, 1082; 47 U.S.C. 154 (i), 303 (e).) [Rule 139, as amended Oct. 29, 1935] 3.99 Maximum power. A licensee of a broadcast station will not be authorized to operate a transmitter with an operating power greater than the maximum rated carrier power of the transmitter.** [Rule 140] 3.100 Data required on percentage modulation. A licensee of a broadcast station claiming a greater percentage of modulation than the fundamental design indicates can be procured, shall submit full data showing the antenna input power by direct measurement and complete information, either oscillograms or other acceptable data, to show that a modulation of 75 percent or more, with not over 10 percent combined audio harmonics, can be obtained with the transmitter operated at the maximum authorized power.*+ [Rule 141] 3.101 Operating power same as licensed power. The licensee of a broadcast station shall maintain the operating power of the station in exact accord with its licensed power at all times except that in an emergency when, due to causes beyond the control of the licensee, it becomes impossible to operate with the full licensed power, the station may be operated at reduced power for a period of not to exceed 10 days, provided that the Commission and the inspector in charge shall be notified in writing immediately after the emergency develops.* [Rule 142] 3.102 Indicating instruments. Each broadcast station shall be equipped with suitable indicating instruments of accepted accuracy 18 The specifications pursuant to paragraph (d), are as follows: (a) A DC meter for setting the average rectified carrier at a specific value and to indicate changes in carrier intensity during modulation. (b) A peak indicating light or similar device that can be set at any predetermined value from 50 to 120 percent modulation to indicate on positive peaks, and/or from 50 to 100 percent negative modulation. (c) A semi-peak indicator with a meter having the characteristics given below shall be used with a circuit such that peaks of modulation of duration between 40 and 90 milliseconds are indicated to 90 percent of full value and the discharge rate adjusted so that the pointer returns from full reading to 10 percent of zero within 500 to 800 milliseconds. A switch shall be provided so that this meter will read either positive or negative modulation and, if desired, in the center position it may read both in a full-wave circuit. The characteristics of the indicating meter are as follows: Speed-The time for one complete oscillation of the pointer shall be 290 to 350 milliseconds. The damping factor shall be between 16 and 200. The useful scale length shall be at least 2.3 inches. The meter shall be calibrated for modulation from 0 to 110 percent and in decibels below 100 percent with 100 percent being 0 DB. The accuracy of the reading on percentage of modulation shall be ±2 percent for 100 percent modulation, and ±4 percent of full scale reading at any other percentage of modulation. (d) The frequency characteristics curve shall not depart from a straight line more than % DB from 30 to 10,000 cycles. The amplitude distortion or generation of audio harmonics shall be kept to a minimum. (e) The modulation meter shall be equipped with appropriate terminals so that an external peak counter can be readily connected. (f) Modulation will be tested at 115 volts ±5 percent and 60 cycles, and the above accuracies shall be applicable under these conditions. (g) All specifications not already covered above, and the general design, construction, and operation of these units must be in accordance with good engineering practice. Page 144 **For statutory and source citations, see note to § 3.1. to measure the antenna current, direct plate circuit voltage, and the direct plate circuit current of the last radio stage. These indicating instruments shall not be changed or replaced, without authority of the Commission, except by instruments of the same type, maximum scale reading, and accuracy.19*+ [Rule 143] 19 The Broadcast Division has issued the following instructions relative to indicating instruments used by broadcast stations in compliance with § 3.102: Instruments indicating the plate current or plate voltage of the last radio stage, (linear scale instruments) shall meet the following specifications: 1. Length of scale shall be not less than 2310 inches. 2. Accuracy shall be at least two percent of the full scale reading. 3. The maximum rating of the meter shall be such that it does not read off scale during modulation. 4. Scale shall have at least 40 divisions. 5. Full scale reading shall not be greater than five times the minimum normal indication. Instruments indicating the antenna current shall meet the following specifications: 1. Instruments having logarithmic or square law scales. a. Shall meet same requirements as 1, 2, and 3 above for linear scale instruments. b. Full scale reading shall not be greater than three times the minimum normal indication. c. No scale division above one-third full scale reading (in ampere) shall be greater than 30 of the full scale reading. (Example: an ammeter meeting requirement (a) above having full scale reading of six amperes is acceptable for reading currents from two to six amperes provided no scale division between two and six amperes is greater than 30 of six amperes, 0.2 amperes.) 2. Radio frequency instruments having expanded scales. a. Shall meet same requirements as 1, 2 and 3 for linear scale instruments. b. Full scale reading shall not be greater than five times the minimum normal indication. c. No scale division above % full scale reading (in amperes) shall be greater than 50 of the full scale reading. (Example: an ammeter meeting the requirement (a) above is acceptable for indicating currents from one to five amperes provided no division between one and five amperes is greater than ‰0 of five amperes, 0.1 ampere.) d. Manufacturers of instruments of the expanded scale type must submit data to the Commission showing that these instruments have acceptable expanded scales, and the type number of these instruments must include suitable designation. 3. Antenna ammeters employing vacuum provided: tube rectifiers are acceptable a. The indicating instrument meets all the above requirements for linear scale instruments. b. Data are submitted under oath showing the unit has an over-all accuracy of at least two percent of the full scale reading. c. Thermocouple type ammeter meeting above requirements 1 a, b and c is installed at the same point in the antenna circuit as the vacuum tube ammeter. d. The calibration of the vacuum tube ammeter is checked against the thermocouple ammeter at least once a week (the thermocouple ammeter may be so connected that it is short circuited or open circuited when not actually being read). 4. Remote reading ammeters. a. Shall meet the same requirements as for the regular instruments. b. Shall be connected at the same point in the circuit. c. The calibration shall be checked against the regular meter at least once a week (the regular meter may be so connected with a switch that it is short circuited or open circuited when not actually being read). d. All remote reading instruments, including the vacuum tube type, shall be connected to the antenna circuit through a properly designed electrostatically **For statutory and source citations, see note to § 3.1. Page 145 3.103 Frequency maintenance 50 cycles. Each broadcast station shall be so operated that the frequency is maintained between the limits of 50 cycles per second above to 50 cycles per second below the assigned frequency.*t [Rule 144] 3.104 Frequency checking device. The licensee of a broadcast station shall make provision for the checking of the frequency of the emitted wave by means independent of the frequency control of the transmitter and capable of the accuracy specified in § 3.103.20 *† [Rule 145] shielded current transformer except in case a shunt excited antenna is employed, in which case the transmission line current meter may be considered as the remote meter provided the transmission line is terminated directed into the excitation circuit feed line which shall employ series tuning only (no shunt circuits of any type shall be employed) and insofar as practicable the type and scale of the transmission linemeter should be the same as those of the excitation circuit feed linemeter. Any method of providing a remote meter different from the above shall be submitted to and approved by the Commission before the indications thereof may be logged as the antenna current. Stations determining power by the indirect method may log the transmission line current in lieu of the antenna current, provided the instrument meets the above requirements for antenna ammeters, and further provided that the ratio between the transmission line current and the antenna current is entered each time in the log. In case the station is authorized for the same operating power for both day and nighttime operation this ratio shall be checked at least once daily. Stations which are authorized to operate with nighttime power different from the daytime power shall check the ratio for each power at least once daily. No instrument indicating the plate current or plate voltage of the last radio stage, the antenna current or the transmission line current when logged in lieu of the antenna current shall be changed or replaced without written authority of the Commission, except by instruments of the same make, type, maximum scale reading and accuracy. Requests for authority to change an instrument may be made by letter or telegram giving the manufacturer's name, type number, serial number and full scale reading of the proposed instrument and the values of current or voltage the instrument will be employed to indicate. Requests for temporary authority to operate without an instrument or with a substitute instrument may be made by letter or telegram stating the necessity therefor and the period involved. No instrument, the seal of which has been broken, shall be employed. Repairs and recalibration of instruments shall be made by the manufacturer, by an authorized instrument repair service of the manufacturer or by some other properly qualified and equipped instrument repair service. In either case the instrument must be resealed with the symbol or trade mark of the repair service and a certificate of calibration supplied therewith. Since it is usually impractical to measure the actual antenna current of a shunt excited antenna system, the current measured at the input of the excitation circuit feed line is accepted as the antenna current. [FCC, BD, Nov. 9, 1937] 20 The Commission has approved the following types of monitors for use by broadcast stations: Page 146 1451 1452 Quartz Plate Type 376-J or L.. **For statutory and source citations, see note to §3.1. 3.105 Changes and new equipment. The Commission will authorize the installation of new transmitting equipment in a broadcast station or changes in the frequency control of an existing transmitter only if such equipment is so designed that there is reasonable assurance that the transmitter is capable of maintaining automatically the assigned frequency within the limits of 50 cycles per second above to 50 cycles per second below the assigned frequency.*+ [Rule 146] 3.106 Changes in frequency control. New automatic frequency control equipment and changes in existing automatic frequency control equipment that may affect the precision of frequency control or the operation of the transmitter shall be installed only upon authorization from the Commission.*+ [Rule 147] 3.107 Auxiliary transmitter. Upon showing that a need exists for the use of an auxiliary transmitter 21 in addition to the regular transmitter of a broadcast station, a license may be issued therefor provided that: (a) An auxiliary transmitter shall be installed only at the same location as the main transmitter, except upon satisfactory showing of technical necessity therefor the Commission may authorize another location. (b) A licensed operator shall be in control wherever an auxiliary transmitter is placed in operation. (c) The auxiliary transmitter shall be maintained so that it may be put into immediate operation at any time upon failure of the main transmitter, or upon request by a duly authorized Government representative. (d) The auxiliary transmitter shall be tested at least once each week to determine that it is in proper operating condition, and that it is adjusted to the proper frequency. A record shall be kept of the time and result of test. Tests shall be conducted only between 1 a. m. and 12 noon. (e) The auxiliary transmitter shall be equipped with satisfactory control equipment which will enable the maintenance of the frequency All regulations applying to broadcast transmitting equipment shall apply also to an auxiliary transmitter. Type 60.. 1457 PM-125-A. 1458 1459 1460 *For statutory and source citations, see note to § 3.1. Page 147 |