The Secretary of State to the Canadian Ambassador

DEPARTMENT OF STATE

WASHINGTON
Dec 24 1947

EXCELLENCY:

I have the honor to refer to discussions in Atlantic City, New Jersey, between representatives of the Government of Canada and representatives of the Government of the United States concerning the matter of a mutual understanding as to engineering standards applicable to the allocation of standard broadcasting stations in the band of frequencies extending from 540 to 1600 kilocycles.

As a result of those discussions, the Government of the United States agrees to enter into an arrangement with the Government of Canada, effective as of the date of their reply, permitting the mutual application of the following engineering standards which will be considered as amending those engineering standards already in effect between the United States and Canada by virtue of provisions set forth in the North American Regional Broadcasting Agreement signed at Habana, Cuba, on December 13, 1937, [1] as continued in application by the terms of the Interim Agreement (Modus Vivendi, Washington, February 25, 1946.) [2]

"1. 10% Skywave Signal Range Curves, 540 kilocycles to 1600 kilocycles, incorporating latitude effect.

"The attached family of curves entitled '10% Skywave Signal Range, 540 kilocycles to 1600 kilocycles', designated Figure 1-A, showing resultant skywave fields from an antenna of height H=0.311 wavelength radiating 100 milivolts per meter at the angle → (theta) pertinent to transmission by one reflection, will be recognized as acceptable for use in lieu of the 10% skywave curve appearing in Appendix V of the North American Regional Broadcasting Agreement, in computing signal intensities at the station receiving interference. It is further recognized that the 10% Skywave Signal Range Curves, 540 kilocycles to 1600 kilocycles, will be applied only to allocation matters on regional channels, and is not considered ap

Treaties and Other International Acts Series 1553; 60 Stat. 1862.

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plicable to allocation matters as between Class II stations on clear channels, in which cases Appendix V will be controlling.

"2. Angles of Departure versus Transmission Range.

"(a) The attached family of curves entitled 'Angles of Departure versus Transmission Range' for use in the band 540 kilocycles to 1600 kilocycles will be recognized as acceptable for use concurrently with the 10% Skywave Signal Range Curves (Figure 1-A) for determining the value of an interfering signal to an existing station.

"(b) The antenna system's maximum theoretical radiated field which exists between the limits defined by curves 4 and 5 for the pertinent angle of departure (theta) will be used

to compute, from Figure 1-A, the interfering signal.

"3. 50% Root-Sum-Square.

"(a) Objectionable interference shall be deemed to exist to
a station when the root-sum-square value of interfering field
intensities, except in the case of Class IV stations on local
channels, is increased to exceed that value obtained by con-
sidering the signals in order of decreasing magnitude, add-
ing the squares of the values and extracting the square root
of the sum, excluding those signals which are less than 50%
of the root-sum-square value of the higher signals already
included.

"(b) The root-sum-square value will not be considered to
be increased when a new interfering signal is added which
is less than 50% of the root-sum-square value of the inter-
ference from existing stations, and which at the same time
is not greater than the smallest signal included in the root-
sum-square value of interference from existing stations.
"(c) It is recognized that application of the above '50% ex-
clusion' method of calculating root-sum-square interference
may result in some cases in anomalies wherein the addition
of a new interfering signal or the increase in value of an
existing interfering signal will cause the exclusion of a
previously included signal and may cause a decrease in the
calculated root-sum-square value of interference. In such
instances, the following alternate method for calculating the
proposed root-sum-square values of interference will be em-
ployed wherever applicable.

"(d) In the cases where it is proposed to add a new inter-
fering signal which is not less than 50% of the root-sum-
square value of interference from existing stations or which

is greater than the smallest signal already included to obtain this root-sum-square value, the root-sum-square limitation after addition of the new signal shall be calculated without excluding any signal previously included. Similarly, in cases where it is proposed to increase the value of one of the existing interfering signals which has been included in the root-sum-square value, the root-sum-square limitation after the increase shall be calculated without excluding interference from any source previously included.

"(e) If the new or increased signal proposed in such cases is ultimately accepted, the root-sum-square values of interference to other stations affected will thereafter be calculated by the '50% exclusion' method without regard to the alternate method of calculation.

"(f) The 50% root-sum-square rule is recognized as applicable between any and all Class III stations on regional channels and between only Class II stations on clear channels. I suggest that, if an agreement in the sense of the foregoing paragraphs is acceptable to the Government of Canada, this note and your reply thereto in similar terms be regarded as constituting the terms of an understanding on the subject between the two Governments. Accept, Excellency, the renewed assurances of my highest consideration.

For the Acting Secretary of State:

GARRISON NORTON

Enclosures:

Two Graphs as follows:

1. "10% Skywave Signal Range, 540 kilocycles to 1600 kilocycles".

2. "Angles of Departure versus Transmission Range".

His Excellency

HUME WRONG,

Ambassador of Canada.