NAB reports (Jan-Dec 1948)

Antenna Performance Certain minimum values of radiation in millivolts per meter per kilowatt at one mile for each class of station are set forth in the present Treaty. Due to disagreement be¬ tween the various countries as to new values and the manner in which such values may be irsed with respect to predicting interference from new stations, no recommendations were made and the views of each country were made part of the record. 650 Mile Rule The United States desired that the minimum value of antenna efficiency in millivolts per meter per kilowatt at one mile should be increased for each class of station to be con¬ sistent with those values encountered in actual measured installation. Cuba and Mexico desired a method of com¬ puting antenna efficiency whereby the theoretical value of millivolts per meter at one mile for an antenna system may be notified for purposes of estimating interference without adherence to minimum or maximum values. Both Mexico and Cuba proposed the elimination of the present 650-mile border rule for the location of Class II stations. Definitions It was recommended that the following definitions be accepted : Standard Broadcast Channel The term “standard broadcast channel’’ means the band of frequencies occupied by the carrier and two side bands of a broadcast signal with the cari'ier frequency at the center. Channels shall be designated by their assigned carrier frequencies. Assignment of Carrier Frequencies* The carrier frequencies assigned to standard broadcast stations shall begin at 540 kilocycles per second and be in successive steps of 10 kilocycles per second to and including 1600 kilocycles per second. No intermediate frequency shall be assigned as the carrier frequency of any broadcast station. Band Width of Emissions * The band width of emissions is not fixed provided that objectionable interference is not created. Ground Wave Signal The rafliated signal which is propagated close to the surface of the earth and is not reflected back from the ionosphere. Power The power of a standard liroadcast station is the un¬ modulated radio frequency power expressed in watts or kilowatts supplied to the antenna system. Spurious Radiations Spurious radiations from a standard broadcasting trans¬ mitter are the radio frequency harmonics, audio frequency * These provisions were considered with the definition of ‘‘standard broadcast channel’’ because of their close substantive relationship with that definition. It was recosnizeil that they may be regarded a.s operating requirements rather than defini¬ tions in a strict sense. harmonics or any other emissions or modulation products not necessary in order to render the desired broadcasting service and may result in the generation of steady state or transient components capable of producing objectionable in¬ terference. Standard Modidation The standard form of modulation is amplitude modulation with an unsuppressed carrier of constant amplitude yielding two symmetrical sidebands. 10% or 50% Signals General By a 10% (or 50%) skywave field intensity is meant that level of field intensity exceeded by the hourly median field intensities in some specified interval of calendar time for 10% (or 50%) of the nights of that calendar interval. The hour of the night to which the “hourly median’’ refers is the hour centered on the instant of time two hours after the latest sunset on the transmission path. Radiated Field Intensity The radiated field intensity in a specified direction is the inverse distance field in millivolts per meter at one statute mile (or the international equivalents in kilometers). Frequency Tolerance and Stability The operating frequency of each broadcast station shall be maintained to within 20 cycles per second of the assigned frequency, and shall not vary perceptibly over short periods of time under all conditions of operation. Elimination of Spurious Radiations In the event objectionable interference results from spurious radiations, the countries concerned shall cooperate by taking whatever steps are necessary to eliminate such interference. Determination of Power The power of a station shall be determined by taking the l)roduct of the square of the current at the point of input to the antenna system and the total resistance at that point. U. S. Proposes Additional Standards The United States in closing the Conference stated in part: “It is the opinion of the delegation of the United States that those of us in the NARBA should not be content to rest on our laurels but should continue to maintain our leadership for the rest of the world in terms of regional agreements as they pertain to broadcasting. . . . “We recommend that those of us participating in this meeting of technicians also recommend to our respective countries that they consider carefully the desirability of including in the final recommendations they submit for the forthcoming Conference in Canada inclusion of certain Standards of Good Engineering Practice for the new NARBA, directed generally toward such items as: “Uniform methods of making field intensity measurements and recordings. “Correct and uniform method of evaluating and analyzing field intensity measurements and recordings. [6]