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The United States presented for discussion item by item the new 10% and 50% skywave curves, the angle of de¬ parture curves, the Class I-B 50% reference contour versus latitude curve, adjacent channel ratios, and proposed that elimination of the 1800 and 2800 mile rules covering Class I-B stations be considered. Aside from the fact that agree¬ ment in principle was reached on the RSS rule, no extended discussion took place.
Canada and Cuba approved of the inclusion in a new treaty of the U. S. proposed “50% RSS exclusion rule” for making additional assignments. Mexico agreed in principle to the RSS rule but reserved stating views on the percentage figure.
Items on which substantial or complete agreement was reached are as follows:
Skywave Signal
A general definition was approved for “skywave signal” in lieu of the present definition for “secondary service area.” The new skywave signal definition is as follows :
Skywave Signal
A radiated signal which is reflected back from the iono¬ sphere.
Class III Stations
The distinction between Class III-A and Class III-B sta¬ tions is of no further use and should be deleted.
Calculations of Groundwave Signals
For the purpo.se of calculating ground wave signal strength, the adoption was recommended of 20 new curves (families of curves) in lieu of the one curve now contained in Appendix IV of the jiresent NARBA (FCC AM Stand¬ ards of Good Engineering Practice, Appendix I, Graphs 1 to 20, inclusive). With a reservation on the part of Mexico, a method of carrying out ground wave field intensity meas¬ urements was adopted. In connection with determining groundwave interference to groundwave service, the follow¬ ing was adopted:
“In cases involving interference from two or more groundwave signals, the largest undesired signal will be considered to determine the existence or absence of interference at any point.”
(Note: This was adopted in lieu of a complex RSS system.)
North American Regional Broadcasting Engineering Committee (NARBEC)
Continuance of the NARBEC as proposed by Canada and the United States was recommended for favorable con¬ sideration. Mexico abstained from consideration in the matter of NARBEC since it is not now a member of that committee.
Adjacent Channels
Canada proposed continuance of the present NARBA adjacent channel ratios of 2:1 (desired to undesired) but would agree to the 1:1 ratio proposed by the United States. Agreement could not be reached on the ratio of signals 20 kc. removed. Canada and the United States agreed that the present 30 kc. ratio be deleted, but no agreement was
reached on the U. S. proposal that stations not be assigned with less than 40 kc. separation if the area enclosed by the 25 mv/m groundwave contours of the two stations over¬ lap, nor was agreement reached on the proposal that no station will be assigned with less than 30 kc. frequency separation if the areas enclosed by the 25 mv/m groundwave contours of either overlaps the area enclosed by the 2 mv/m groundwave contour of the other.
Determination of Objectionable Interference
Although specific ways and means of determining the existence or absence of objectionable interference were not decided upon, it was agreed that provision for such deter¬ mination should be included in the recommendation as follows :
The present and extent or absence of objection¬ able interference from stations on the same channel or adjacent channel shall be:
1. Determined by actual measurements of the in¬ terfering signal obtained by the methods pre¬ sented in this agreement (new NARBA).
(Note: No method fully agreed upon.)
2. Estimated b}" reference to the propagation curve
in Appendices .... and . ( Present Ap¬
pendices IV and V.)
(Note: No specific skywave curves were agreed upon.)
Mileage Separation Tables (Appendix VI, Present NARBA)
All countries were in agreement that the mileage sepa¬ ration tables have been of little or no use since the effective date of the NARBA and therefore should not be included in the new Treaty.
Notification
Notification of new, or change in existing, assignments of one country to the others has in the past required certain minimum technical data. The desirability of the submission of more detailed engineering data with notification of sta¬ tion assignments was generally recognized and the follow¬ ing data was recommended for submission :
“. . . showing, with respect to each station, its call signal, geographical location of the center of the an¬ tenna in latitude and longitude, frequency, power and antenna characteristics, including electrical and phys¬ ical dimension of directional as well as omnidirectional antenna systems (for directional systems horizontal and vertical radiation patterns for both day and night operation shall be furnished; vertical pattern need only be shown for the directions in which protection is recpiired) .”
20:1 Co-channel Ratio of Desired to Undesired Signal
It was agreed, without extended discussion, that perhaps from some viewpoints a higher ratio might be desirable, but that for practical purposes continuance of the 20:1 ratio should be recommended.
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