India Radio Research Articles

On the Need for Revision of Noise Grades for India

AbstractMeasurement of atmospheric noise in the frequency range 2·5–9·5 mc./s. has been in progress at the Research Department of All India Radio, New Delhi, since November 1955. The measured data have been compared with the predicted ones for Delhi from C.C.I.R. Report No. 65. It is observed that the predicted values are invariably low and the difference between the two has, at times, exceeded 40 db. It is concluded that the noise grades predicted in the C.C.I.R. report do not represent conditions prevailing in India and there are sufficient justifications to warrant their revision.

Ionospheric Absorption Over Delhi

An automatic method of measuring ionospheric absorption on vertical incidence pulsed transmissions has been developed at the Research Department of All India Radio. The equipment and some preliminary observations have been described earlier. Regular measurements by this recorder were commenced in June 1954 and are still in progress. The present paper deals with the analysis of further measurements made till October 1957.Absorption was measured on 5 mc./s. every day at midday and at different times on other occasions. The analysis of data reveals the following: (a) Running average of the monthly midday absorption is well correlated with corresponding running average of sunspot numbers; (b) the diurnal variation factor n has been evaluated on some occasions and has been found to lie within the range 0·33–1·13 with more than 80 per cent of values between 0·33 and 0·9; (c) in the evaluation of relaxation time two maxima of absorption, one in the forenoon and the other in the afternoon, have been occasionally observed although there are a few clear instances of only one post-noon maximum; (d) attempt has been made to work out seasonal variation of midday absorption from the measurements. The results described in the paper are rather tentative as measured values of ionospheric absorption spread over a large number of years are required for arriving at definite conclusions.

Automatic Reverberation Time Recorder

AbstractThe method of measurement of reverberation time by tracing decay curves is tedious though accurate. Occasions frequently arise when the need for a quick determination of reverberation time vs. frequency curve is felt. An equipment constructed in the Research Department, All India Radio, which can plot the reverberation time vs. frequency curve of an enclosure under test, in a relatively short time, is described. The time taken for 40 db decay is measured and is taken as two-thirds the value of reverberation time, assuming an exponential decay of sound energy. The value of reverberation time thus obtained is indicated on a calibrated meter and also plotted on waxed paper as a straight line whose length is proportional to the value of reverberation time. A number of such lines is obtained automatically at close intervals, each line representing the value of reverberation time a frequency slightly higher than the frequency corresponding to the previous line. Since all these lines have the same zero a...

All India Radio and the First Five Year Plan

All India Radio and the First Five Year Plan

Peak Limiting Amplifiers

AbstractA discussion of the requirements for controlling the wide range of amplitude of signals, encountered in broadcasting and other similar telecommunication services, is at first presented. It has been found that a combination of manual and electronic control is found necessary to keep the modulation high without overloading the system. The electronic control is carried out with the help of variable gain amplifier, commonly known as peak limiting amplifier. A limiting amplifier based on some desirable performance characteristics, as evolved here, which has been designed and constructed in the Research Department, All India Radio, is described, in detail, with particular reference to its dynamic behaviour.

Measurement of Soil Conductivity by the Wave-Tilt Method

A number of measurements of soil conductivity by the wave-tilt method were carried out in and around Delhi utilizing medium-wave signals from the Delhi transmitters of All India Radio. The results of these measurements are presented in this paper. It is of interest to note that, except in the case of rocky soil, the soil was everywhere found to be inhomogeneous.

Thermal Expansion of Ionospheric Layer and Temporary Morning Disappearance of Radio Signals

IT is usually assumed that under normal conditions of the ionosphere, if a radio signal is received after ground sunrise, it is likely to maintain its strength until absorption in the ionospheric region becomes pronounced during the day. It has often been found, however, during our observations of fading, that the reception of signals on shorter wave-bands completely ceases for about an hour or more after ground sunrise. The present communication is to show that thermal expansion of the F2-region may be sufficient to overcome the enhancement of ionization caused by increase in solar altitude with advance of the day. To quote a few typical examples out of many occasions, the signals transmitted from All India Radio, Delhi, on December 28, 1946, on 19-m. band were received in Benares (678 km.) until 0711 hr. I.S.T., when they disappeared for about an hour. A similar disappearance of signal on the same waveband was observed on April 11, 1947, at 0750 hr. I.S.T., lasting for about two hours.

Weather Forecasts for Indian Farmers

AN article in Indian Farming of July 1945 by Dr. L. A. Ramdas describes the preliminary steps that have been taken in the Indian Meteorological Department for the establishment of a service of weather forecasts for Indian farmers. Dr. Ramdas is able to bring to bear on it the experience he has gained as agricultural meteorologist at Poona. The essence of the problem is how to enable Indian farmers and official weather forecasters to co-operate so that farming operations may, so far as is possible, be timed in such a way as to make the best possible use of periods of favourable weather and avoid the worst consequences of unfavourable weather. The official forecaster is often able to supplement the fanner's local knowledge of weather by diagnosing the significance of air movements and changes of cloud over a wide area ; but he in turn must know what crops are being grown in different parts of the country and what are the critical periods of their growth and harvest. Here it is the turn of the farmer to help the forecaster. Dr. Ramdas describes fully a long series of questions that have been put to the agricultural departments in the Provinces and the Indian States, and outlines the scheme of wireless forecasts to be used. The forecasting will be done from seven regional centres, and will be broadcast daily by the All India Radio Broadcasting Stations. The scale of the intended system is much greater than that of any seen hitherto in India.

Manufacture of Radio Equipment in India

THE August issue of the Journal of Scientific and Industrial Research published in Delhi contains an article by S. P. Chakravarti entitled “Manufacture of Wireless Apparatus in India”. The growth of radio in India began in 1926, when two low-power broadcasting stations were set up in Bombay and Calcutta. In the following seven years radio telegraph and telephone beam stations were installed linking India with Great Britain and later with Japan. Since 1936, a broadcasting service has been operated on progressive lines under a separate department known as All India Radio. In spite of these developments, however, the production in India of radio equipment, including broadcasting receivers, prior to the outbreak of war in 1939, was confined to the assembly of sets from imported parts and components. In the following years these imports became increasingly difficult to obtain, and many firms had to abandon the manufacture of radio sets. In 1942, a systematic examination of the manufacturing position was carried out by the Government of India in connexion with the development of military radio sets. Investigations leading to the development of certain components from materials available in India have since been carried out under the auspices of the Radio Research Committee of the Board of Scientific and Industrial Research. It is now known that sufficient facilities for the manufacture of all components except valves exist in India, and that the organisations-some twenty in number-possessing manufacturing facilities are in urgent need of special basic materials and appliances.