33 BRITISH STATEMENT CONCERNING TOPIC 5 OF THE PROGRAM 1 BRITISH RADIO-FREQUENCY STANDARDS AND COMPARISONS OF The development of radio-frequency standards in Great Britain is carried out by the National Physical Laboratory under the direction of the Radio Research Board of the Department of Scientific and Industrial Research. The primary frequency standard is based on the principle of the Abraham-Bloch multi-vibrator. The apparatus consists of two multi-vibrators, one of which has a frequency of 1 kc/s while the other has a frequency which is generally of 20 kc/s. The The essential quality which characterizes the frequency meter is the manner in which frequencies are maintained constant. second multi-vibrator is maintained synchronized with the first one with the aid of the twentieth amplified harmonic of the low-frequency multi-vibrator. This is obtained with a special circuit and a tubeamplifying device tuned to a frequency of 20 kc/s. The two multi-vibrators are further controlled by a tuning-fork, electrically excited, and whose frequency is 1 kc/s. The impulsions of these two multi-vibrators may operate a tuned circuit consisting of a standard variable condenser of special design and one set of six self-inductances. In this manner, the tuning may be made with two complete series of harmonics, covering a band of 10 to 1,200 kc/s. A selective amplifier is used to amplify any tuned harmonic. The apparatus operates independently and offers the possibility of measuring and of producing any frequency of the band of 10 to 12,000 kc/s, with an accuracy of approximately 2 per 100,000. When the frequency of the tuning-fork is measured directly on the basis of the time unit, the accuracy may be increased to 1 per 100,000. The apparatus is the national radio-frequency standard and may be used for all standard measurements where an accurate measurement of frequency is desired. With the aid of auxiliary devices, the frequency band may be extended to 50 megacycles per second (6-meter wave-length), without noticeable loss in accuracy. [Original enclosed with letter from the Secretary of the British General Post Office to the Netherland Director General of Posts and Telegraphs, dated July 4, 1929, in which he points out that changes in the present system "are contemplated in the near future." Copy, together with covering letter, enclosed with Circular Letter No. R 30/113, dated August 17, 1929, of the International Bureau of the Telegraph Union, Radiotelegraph Service.-H. F. W.] 1 Standard Wave Transmission The development of the above-described wave-meter enabled the transmission of standard waves of great stability and accuracy by the National Physical Laboratory. The transmissions made cover a band of 30 to 1,000 kc/s. Sixteen different frequencies are transmitted altogether in two programs. Each program is transmitted once a month. A detailed program is contained in Annex 1 attached herewith. The radiated power is not great and decreases considerably with long waves. However, the signals were received in a satisfactory manner at distances of 500 English miles. The extension of waves to higher frequency bands is still under consideration. Under the conditions in which the National Physical Laboratory is operating, the difficulties in making such transmissions with the same accuracy are great, and these emissions are made only when the expense incurred seems justified. A great amount of work has also been done in connection with resonators and piezo-electric oscillators. Some details concerning a number of international comparisons made on a quartz oscillator supplied by the Bureau of Standards appear in Annex 2. From the measurement results in question, the conclusion may be drawn that the measurement of radio-frequencies is carried out under very satisfactory conditions, and that when a sufficiently constant radio-frequency source of any type is at disposal, the frequency of same may be determined with an accuracy of 1 to 2 per 100,000, without resorting to any present radio-frequency standard. The Radio Research Board lately considered the recommendations of the Brussels Conference of the International Radio Telegraph Union, 1928, and it was decided to collaborate by applying the decisions of Committee No. 1 on radio standards. These decisions were as follows: 1. Dr. Hoyt Taylor of the Naval Research Laboratory, Bellevue, Anacostia, Ď. C., will be communicated with for the emission of regular series of short-wave signals (15-meter wave-length or 20 megacycles p/sec.) for the purpose of making international comparisons of frequency standards in the vicinity of that wave-length. 2. Negotiations will be entered into with the British Broadcasting Corporation, and when these will have satisfactory results, the following arrangements will be made with the B. B. C.: (a) To transmit by the radio-broadcasting station of Daventry (5 G B) unmodulated waves enabling international comparison, within the range of the station, of the frequency in the vicinity of the 610 kc/s frequency (492-meter wavelength). (b) To transmit a program of modulated waves by the same station. This modulation must be made with a tuningfork operating very regularly at approximately 1,000 cycles per second. The period and the characteristic of this emission will be such as to permit the frequency comparison of a tuningfork as, for example, that at Brussels, which is used as a standard for all European broadcasting stations and of the wave-checking multi-vibrators. This modulated frequency will be measured with a great accuracy in England by the National Physical Laboratory, and at other places where absolute measurements with great accuracy on the basis of the astronomical time unit may be made. 3. Dr. Hull, formerly of the Bureau of Standards, and at present at the Radio Frequency Laboratories, Inc., Boonton, New Jersey, will be communicated with concerning the loan to the U. R. S. I. of a piezo-electric oscillator with temperature control, of such a quality that it could be forwarded constantly from one national laboratory to another. Annex 1 DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH EMISSION OF STANDARD WAVES FROM THE NATIONAL PHYSICAL LABORATORY (CALL-SIGNAL: 5 HW) Statement Made to the Press on August 17, 1926 In the course of these last three years, an emission of waves, whose length was exactly known, was made to comply with a recommendation of the Radio Research Board of the Department from the wireless station at the National Physical Laboratory in order to provide a way of checking wave-controllers and other devices. This emission was extended to 8 wave-lengths covering a band of 360 to 60 kc/s (833 to 5,000-meter wave-length). The emission was made every two weeks, on Tuesdays in the afternoon, from 3 to 4 p. m., G. M. T. After consultation with the Post Office and other interested groups, steps were taken to increase the use of this service by considerably increasing these emissions. The new emissions will include sixteen different wave-lengths. The emission will be made in two emission groups; each group will be transmitted once every month. One part will be transmitted the first Tuesday of each month between 3 and 4 p. m., G. M. T. The second group will be transmitted the third Tuesday of the month at the same hour. These emissions will take place temporarily according to the following system: (1) It will be announced with Morse signals on continuous waves, on a 1,500-meter wave-length, that an emission of standard waves is going to take place. This warning will be made at 2:55 p. m., G. M. T. (2) Each standard wave will be transmitted as follows: a. Program of short-wave emission for the first Tuesday of each month. The character N followed by a figure indicating the wave-length. This will be repeated three times, followed by a continuous dash lasting 40 seconds. Four such dashes will be thus transmitted, each preceded by the character and the figure, for identification. So far as possible, the dash will begin at the end of the first 20 seconds of the minute and will last until the end of that minute. An interval of 4 minutes will elapse before the following wave will be transmitted exactly in the same manner. b. Program of long-wave emission for the third Tuesday of each month. This emission will be made exactly in the same manner as that for short It is possible that during the intervals, dashes caused by the adjustment and the tuning of circuits on the following wave may be heard. These dashes must not be considered as belonging to the program. The warning will be made by the call CQ 5 HW repeated several times and followed by the words "short (or long) standard wave frequency transmissions, stand by." During one or two months in the year, including five Tuesdays, there will be an interval of three weeks between the emission of the third Tuesday of these months and the following emission. The frequencies transmitted will be of a great accuracy, so that it will be unnecessary to give corrections. The actual frequency will not be transmitted, because the character and the figure are used for that purpose. Note will be taken of the current of the antenna, but will not be transmitted. Information will be supplied with regard to the value of the current, upon request. Notices on the reception of these waves are as follows: RECEPTION OF STANDARD WAVES It goes without saying that the apparatus, which it is proposed to check with the aid of radio waves, is a vacuum tube piezo-resonator of easy adjustment. It is also important to have a receiving station which may be tuned w.th detection devices used in connection with the heterodyne. The most correct manner of checking is to adjust the heterodyne in such a way that the height of the beat note is the same as that of a small tuning-fork, the frequency of which is known. This will not be necessary for high-frequency waves, but for longer waves the point at which no beat note will be heard, will be greater than r. while if use is made of a fixed beat note of say 1,000 cycles per second, the sensitiveness of the receiving station will be intense and the tuning accuracy will be much greater than the heterodyne permits to notice, unless the latter is of a quite special design. The frequency of the beat note must naturally be added to or deducted from the frequency of the standard waves, according to whether the heterodyne is tuned on a smaller frequency or on the greater frequency. It is recommendable to tune the heterodyne at first on a greater wave and then on a smaller wave than the wave received. Then arrangements are made so as to obtain an equality of sound on both sides. It is not necessary to know the frequency of the tuning-fork. The average value between these two indications of the variable condenser of the heterodyne then exactly corresponds to the frequency transmitted. We admit here that there is a linear ratio between the capacity of the condenser and the frequency. If this is not so, there is occasion to make a small correction, in order to obtain the greatest accuracy. When considering emission frequencies, it will be noticed that they are not exact multiples of each other, except for several frequencies which are mutually very remote. In this way, it is possible to obtain standard frequencies which have intermediate values of those now transmitted. Thus, for the long-wave program, it has been possible to tune the heterodyne on a frequency of 33 kc/s during the emission of the standard wave of 66 kc/s. The second harmonic of the heterodyne at 66 kc/s will give beats easy to determine with the standard wave of 66 kc/s. The following intermediate frequencies can all be obtained in such a manner without any difficulty: 2nd harmonics: 33, 43, 57.5, 80, 100, 130, 150, 180, 250, 290, 350, 420, 480. 3d harmonics: 38%, 53%, 66%, 86%, 100, 120, 166%, 233%, 280, 320. If necessary other heterodyne harmonics could be taken, but the abovementioned series permits obtaining almost 50 standard points on a band of 10,000 to 320 meters. Naturally, an heterodyne of shorter waves can be standardized with harmonics of an heterodyne which has already been standardized with short standard waves transmitted. The length of the dashes and their number will permit making two tunings: first, the tuning of the intermediate heterodyne with the standard wave |