FINAL PROTOCAL OF THE EUROPEAN RADIO CONFERENCE, PRAGUE, 1920

A

FINAL PROTOCOL

The European Radio Conference of Prague, after having heard the delegations and experts present, and, in conformity with the reports of its committees, recommends that the administrations agree to the following:

Π

The wave, 1,124 m (267 kc) used by the German criminal police is recognized as carrying on an international service from Germany with other European nations. In accordance with the provisions of Article 5, Paragraph 14, of the Washington Regulations, the waves of 89.5 kc (3,350 m) and 45 kc (6,660 m) are allocated for synoptic meteorological messages.

B

The Conference has decided to request the Czechoslovak Administration to be kind enough to express to the Administration of the Netherlands its desire to have the following questions studied by the C. C. I. Radio at the next meeting at The Hague:

1. The proper separation to be maintained between wave-lengths for radio transmissions of all kinds;

2. Stability control for all radio transmissions;

3. The allocation of short waves for aviation and for the criminal police;

4. The allocation of short waves for national services;

5. Power limitation for broadcast stations and the proper formula to be used for regulating such limitation;

6. Frequency separation in cycles to be maintained between stations in adjacent bands;

7. Study of the organization for a permanent international service for frequency measurements.

C

3. CONCERNING WAVES USED FOR AVIATION

It is desirable that the authorities of all the European countries should study the possibility of restricting the use by aviation of the wave length band above 1,340 m (below 224 kc).

11

LATVIAN PROPOSALS CONCERNING TOPICS 2-6, 8 AND 10-15 OF THE PROGRAM 1

1

(a) POWER OF A TRANSMITTER (TOPIC 2 OF THE PROGRAM)

By power of a transmitter is meant the power transmitted by the antenna of a transmitter because it is the power W (watt) transmitted by the antenna which gives the prime mover of the field.

E (volt/meter) = √/90 W. f (^, d) = 120πJ2 deo(^, d)

where (^, d) = (a+jß)d√R+jPL√S+jPC with unknown constancies.

(b) DEFINITIONS (TOPIC 3 OF THE PROGRAM)

The primary difference between the so-called ultra-short, short, average and long waves is caused by the difference between the proportion, the powder and the propagation of Hertzian waves (threedimensionals) and the two-dimension waves (Tesla) for various wave frequencies.

The Huyghens principle becomes stronger with the frequency.

(c) DEFINITIONS (TOPIC 4 OF THE PROGRAM)

As wireless telegraphy was based, more than 30 years ago, on the Tesla wave, and as the Hertzian waves have been studied only for about a year, under the form of ultra-short waves, we dare only to recommend the study of these short waves by anyone who is in a position to do so.

(d) SUPPRESSION OF INTERFERENCE (TOPIC 5 OF THE PROGRAM)

Many countries have developed their institutions for the checking of frequency-meters. It is desirable that the C. C. I. Radio should

1

[Enclosed with Circular Letter No. R 30/72, dated July 25, 1929, of the International Bureau of the Telegraph Union, Radiotelegraph Service.H. F. W.]

118275-30- -9

coordinate this work and should supply all the necessary informa tion to the administrations of the countries deprived of these institutions.

(e) SUPPRESSION OF INTERFERENCE (TOPIC 6 OF THE PROGRAM)

The C. C. I. Radio must come to an understanding with the countries which are in a position to carry on the permanent checking of the waves.

(f) SUPPRESSION OF INTERFERENCE (TOPIC 8α AND b of the PROGRAM)

Some administrators have developed ultra-selected receivers, up to 4 cycles for example. That is why it is necessary, before defining the distance between various stations of the same service or between different services, to study:

a. The possibilities of reception at approximately x cycles;

b. The possibilities of the stabilization of emissions at approximately x cycles.

(g) SPECIAL STUDIES (TOPIC 10 OF THE PROGRAM)

Each administration must participate in the studies prepared by the C. C. I. Radio on the phenomena mentioned.

(h) LICENSES FOR AMATEURS (TOPIC 11 OF THE PROGRAM)

In order to increase the number of participants in the studies proposed under Topic 10 of the program, it would perhaps be useful to recommend to the administrations to stipulate in the amateur licenses their compulsory participation in the tests which the administration deems useful.

(i) TOPICS RECOMMENDED BY THE PRAGUE CONFERENCE

Strike out the text under Topics 12 and 13 of the program. It is proposed to make these studies according to the indications contemplated under Topics 6-9 of the program.

(j) TOPICS RECOMMENDED BY THE PRAGUE CONFERENCE (TOPIC 14 of

THE PROGRAM)

To leave free the use of ultra-short waves for national services with the reservation that, if these waves should be received by stations of other countries, interfering with their work, it should be indicated to use them also for international services. These inter

ference facts should be brought to the knowledge of the C. C. I. Radio.

(k) TOPICS RECOMMENDED BY THE PRAGUE CONFERENCE (TOPIC 15 OF THE PROGRAM)

One of the following two equivalent values may be designated as the permissible maximum efficiency:

a. The number of watts emitted per square kilometer of the country;

b. The electro-magnetic field at the frontier of the country. This is due to the fact that the formula

for small values of d may be simplified as follows:

W

S

It may be said that E (v/m) or may be used as a basis to express

the efficiency.

In our opinion, 1 watt emitted per square kilometer of the country should be the maximum limit, since 0.5 W emitted per square kilometer already gives a satisfactory reception when using a galena detector.

12

PRELIMINARY BRITISH STATEMENT CONCERNING TOPIC 9 OF THE PROGRAM1

MEMORANDUM BY POST OFFICE ENGINEERING DEPARTMENT

Modern Practice as Regards the Elimination of Emissions Other Than Those Essential to Communication from Radio Transmitters

In this memorandum the remarks have been confined to arc and valve transmitters since it has been mainly with these types that

1

[Enclosed with Circular Letter No. R 30/72, dated July 25, 1929, of the International Bureau of the Telegraph Union, Radiotelegraph Service. For figures annexed to British statement, see French text.-H. F. W.]

the experience of the British Post Office has been acquired. No attempt has been made to define in any way the extent of the interference likely to be caused by either type of transmitter, but rather to point out the main sources of untoward emissions and to give the steps which have been taken to ensure that the extent of these emissions should be reduced to a minimum whilst at the same time preserving the efficiency of the transmitter.

THE ARC TRANSMITTER

It is a matter of common knowledge that the Poulsen arc, if directly connected to an antenna, produces a great deal of disturbance to other wireless users on wave-lengths far removed from that of the arc. This disturbance is of two kinds: (1) the emission of harmonics, i. e., emissions which are definitely tunable and which can be heterodyned to a musical note, and (2) the emission of what has been called mush. The latter manifests itself as a hissing sound in a receiver and is usually found most strongly in the neighbourhood of the harmonic positions.

The cause of harmonics is to be found in the slight departure from sinusoidal form of the current in the oscillating circuit. Suitable design of the arc and the antenna circuit may reduce the harmonics to the same order of strength as those obtained from a valve oscillator of similar power on plain antenna but in practice the harmonics and more especially the mush are still strong enough to cause trouble.

The cause of mush is a little more obscure, but it is probably associated with the irregular frequency of the fundamental wave. The arc is an ionic contrivance and on a plain antenna connexion has a frequency which in the nature of the ionic action inside the arc chamber can not be expected to be very constant. Carson 1 has shown that, if a sine wave has its frequency changed at a sinusoidal rate or in other words undergoes frequency modulation, an infinite series of harmonics of the sum and differences of the fundamental and modulating frequencies is obtained.

When any one harmonic of this series happens to fit in with the harmonic resonant point of the antenna, it gives rise to radiation on that frequency.

With the are the fundamental frequency is undergoing frequent discontinuous changes and it is to be expected that the "harmonic " due to these irregular changes will form a continuous spectrum of disturbance which is ready to emerge at any harmonic resonant point of the antenna.

J. R. Carson, Frequency Modulation," in Proceedings of the Institute of Radio Engineers, 1922, vol. 10, p. 57.