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Coordination of Radiotelephony and Telephony in the International Telephone Service

The International Consultative Committee

Considering: That the use of a radio-broadcasting liaison in a longdistance telephone circuit implies certain special conditions which. lead to particular difficulties which are not met when wire liaisons alone are used;

That a radiotelephone circuit is different from a wire circuit on the following points:

1. A radiotelephone circuit is subject to weakness variations (with the special difficulty of signal fading which characterizes the transmission with very high radio-frequencies).

2. A radiotelephone circuit is affected by noises produced by atmospheric parasites, the intensity of which varies from a negligible quantity up to a value of the same amount as the signal which it is desired to receive.

3. Special precautions are required in the establishment and the maintenance of a radiotelephone circuit in order to prevent, at the receiving station, disturbances caused by the radio transmitter used for the other direction of transmission and by radio transmitters used for other services; in other words, the abnormal singing conditions or diaphony are to be avoided or corrected.

4. In order to maintain the radio-broadcasting liaison under the best conditions as regards transmission, it is necessary to have special means to ensure that the radio transmitter is, as far as possible, always operating at full charge, whatever the nature and the weakness of the extension line connected with the radiotelephone circuit may be.

5. The band of vocal frequencies which the radio-broadcasting liaison may transmit may be limited by one or more of the following conditions:

(a) Necessity of saving frequencies which may be used for radio

transmissions.

(b) Use of a low radio-frequency.

(c) Necessity of using electric filters with the particular transmission system used.

6. A radiotelephone circuit, in general, is a long-distance intercontinental circuit securing a telephone service between two extended systems and therefore is of great importance from the two following points of view:

(a) It is desirable that the characteristics of transmission which one endeavors to attain in the establishment of this radiotelephone circuit should be better than those now prescribed for long-distance wire circuits.

(b) Under the present conditions of the technique, it is not advisable to deprive the public of a very useful service, under the pretext that it does not always meet the degree of efficiency required for longdistance communications from the quality point of view.

Unanimously expresses the following opinion:

1. That the frequency-band transmitted by a radiotelephone circuit should not be below that recommended by the C. C. I. for international long-distance telephone circuits, that is to say, 300-2,500 pps., but it is advisable to secure, if possible, a larger frequency-band and, when this can be done, the radiotelephone circuit should be arranged so as to transmit a frequency-band of at least 200-3,000 pps. Remarks.-Under the present status of the technique, it may be desirable to use temporarily frequency-bands other than those specified above, if there is an improvement in transmission, for example, as a result of a reduction in the volume of noise.

2. That the normal equivalent of a radiotelephone circuit should not exceed the limit recommended for long-distance circuits, that is to say, 1.3 neper or 11.3 decibels, but when this can be done, a radiotelephone circuit should be designed so as to have an equivalent below that value under favorable radio conditions; that, as, under the present status of the technique, it is not possible in practice to maintain always a radiotelephone circuit strictly below the limit of 1.3 neper or 11.3 decibels, a certain margin should be granted when radio conditions are unfavorable, rather than to deprive subscribers of a very useful long-distance service. In case of unfavorable radio conditions, it must be observed that it might be necessary to give up the idea of the extensions of radio-broadcasting liaison by wire liaisons, which are normally possible.

3. That every possible effort should be made in order to reduce the level of noise in relation to that of the voice, by using radio devices such as directed antennas, etc. However, it will be necessary to tolerate large variations of the noise level on a radiotelephone circuit. Moreover, under the present status of the technique neither a maximum value of the ratio between the intensity of the noise and that of the voice nor a method of noise measurement can be recommended yet.

Temporarily, the following values may be taken as a guide for the noise level on a radiotelephone circuit:

(a) Under average radio conditions, an average noise tension up to 25 millivolts or less in 600 ohms at the zero transmission level may

be reckoned, which corresponds to an average power of 0.001 milliwatt, with a unidirectional current.

(b) Under unfavorable radio conditions, an average noise tension up to 200 millivolts in 600 ohms at the zero level may be tolerated, if the extension circuits, including subscribers' circuits, are of a sufficiently good quality (this noise tension corresponds to an average power of 0.067 milliwatt, unidirectional current). It must be ascertained that the noise tension is not such that the echo eliminators, which may be fitted on the extension circuits, would be put into operation.

4. That the extension circuits connected with a radiotelephone circuit should be in conformity with the various recommendations of the C. C. I. regarding the equivalent of transmission, distortion, noise, echoes and transitory phenomena on ordinary wire circuits, particularly as follows:

(a) The equivalent between a subscriber and the terminals of the radiotelephone circuit must not exceed 1.3+1.0-2.3 nepers or 20 decibels. The total transmission equivalent between two subscribers, including the radiotelephone circuit and, if any, the line amplifiers, must not exceed 3.3 nepers or 30 decibels.1

(b) The noise tension must not exceed the temporary value of 5 millivolts in 600 ohms at the transmission level 1 (proposal of the Third Commission of Reporting Officers at Cologne in reply to Question 16).

(c) The effects of echoes must not exceed the limits shown by the curves and the opinions of the C. C. I. which appear on pages 66-68 of the Green Book.

(d) The duration of transitory phenomena in extension circuits must be such that the total duration of a transitory phenomenon for any frequency of the band to be transmitted and for the complete circuit between subscribers (including the radiotelephone circuit and the two extension lines) should not exceed 30 milliseconds.

5. That if a radiotelephone circuit is using a band of rather low radio-frequencies which makes it necessary, in view of the crowding of the ether, to use the same radio-frequency band for the transmission in both directions, this radiotelephone circuit should be fitted with a voice-commutating device, so as to avoid singing or disturbances caused by a radio-transmitting station on the radioreceiving station.

Although it is not always essential from the technical point of view to use a voice-commutating device when the same frequency band is not used for radio transmission in both directions (which is

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the present practice for very high radio-frequencies), it is desirable to have a radiotelephone circuit fitted with such devices, so as to be able to use that circuit

(a) with a small equivalent of transmission, and

(b) to connect two long-distance extension circuits which, in the absence of such a device, would constitute a liaison with excessive echo effects.

6. That, under the present status of the technique and in order to maintain the voice at the necessary levels on the radio-broadcasting liaison, a special technical operator should supervise the transmission in a continuous manner, from a post fitted with instruments showing the volumes of voice and of disturbing noises; that this operator should be able to adjust the volume of sound, so as to charge completely the radio transmitter and that he should proceed with all necessary adjustments of the conditions of the circuit (operating also the voice arrangement) so that the conditions of the radiotelephone circuit may be at all times in a proper ratio between the volume of sounds of the voice and the intensity of disturbing noises.

7. That, particularly when very high radio-frequencies are used, the radiotelephone circuit should be fitted with automatic increasing adjusting apparatus, so as to compensate automatically and as far as possible the fading of radio signals.

8. That the terminal equipments of the radiotelephone circuit be such that the latter might be connected as any circuit with any other type of circuit.

Please accept [etc.]

INTERNATIONAL CONSULTATIVE COMMITTEE
ON LONG-DISTANCE TELEPHONE COMMUNICATIONS

The Secretary General
GEORGES VALENSI

5

PRELIMINARY NETHERLAND STATEMENT CONCERNING TOPIC 2 OF THE PROGRAM 1

POWER OF A TRANSMITTER

In the international exchange of information on radio-emission devices, the power of the emitters at the disposal of the administration is often mentioned.

1 [Enclosed with Circular Letter No. R 30/53, dated July 16, 1929, of the International Bureau of the Telegraph Union, Radiotelegraph Service.H. F. W.]

But a clear and universally adopted definition of what is to be understood by the expression "power of an emitter," has not yet been adopted.

The aim of what follows is exclusively to determine the conception of the power of a so-called emitter, that is to say, without

antenna.

(The importance of the expression "power of an emitter," including the antenna, especially for ultra-short waves, is considered under Topic 4 of the Program.)

It has been noted in practice that even with this restriction, the conceptions of the various administrations are still different. Indeed, taking for example the tube transmitters, an administration considers the power of the plate circuit of the last tube, while another administration takes the total power of the tubes as a basis. The great inconvenience of this state of things is that one is almost always uncertain about the value to be attributed to the information of that nature.

According to the opinion of the Netherland Administration, it is thus important to come to an understanding in order to arrive at a uniform definition on this subject which will henceforth be applied to international information. In view of the difficulty in giving a general definition for all types of transmitters, the Netherland Administration considers it advisable to recommend a classification according to four principal systems of radio emission.

As to the definitions themselves, it is advisable to endeavor to have a basis which would be easy and simple to measure and which would not give rise to various interpretations.

The expression "power of a transmitter" could mean:

(1) For tube transmitters: The power of the plate circuit of the last row of emission.

This power (that is to say, the product of the current and the anodic tension) will be measured by using measuring apparatus with continuous current. The value thus obtained presents the advantage of being applicable to the telephone-transmission systems as well as to the telegraph-transmission systems. It may be admitted that the above-mentioned value is not subject to variations resulting from modulation, unless the latter does not give any distortion.

(2) For arc transmitters: The power transmitted at the arc, that is to say, the total power decreased by the power absorbed by the magnets.

(3) For high-frequency alternators: The power transmitted at the axle of rotation of the high-frequency alternator.

In the case where the axle is actuated by an electric motor, which is frequently the case, the scope of the proposed definition is spe

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