NOPR Collection:

Atmospheric Radio Noise Intensities in the Northern & Eastern Regions of India

1972-09-01T00:00:00Z

Title: Atmospheric Radio Noise Intensities in the Northern & Eastern Regions of India Authors: Ghosh, B. B. Abstract: Some of the already measured values of atmospheric radio noise· field strengths (ARN-FS) for Delhi (28°35'N, 77°05'E) and Gauhati (26°10'N, 91°40'E) have been utilized, with a modified form of the available mathematical expression, to calculate the expected ARN·FS for a number of frequencies in the range 0.3-20·0 MHz for different time blocks and seasons. The ARN-FS values thus calculated have been compared graphically with the measured values and also with those predicted in CCIR Report No. 322. They are found to be almost of the same order of magnitude and form, for all frequencies, times and seasons except that the predicted noise shows very low values in some lower hf bands of frequencies during daytime. It is pointed out that the basis for prediction at these frequencies during daytime is not quite what it should be to account for the actual conditions for propagation of ARN over the Indian landmass. Besides, in view of the fact that both the predicted and calculated ARN-FS are almost within acceptable limits for all other frequencies and times, the method of calculation outlined here is considered to be quite convenient to estimate ARN-FS existing in the northern and eastern regions of India under actual conditions, for practical applications. Page(s): 236-240

Statistical Analysis of the Amplitude of Radio Waves Reflected from the Ionosphere

1972-09-01T00:00:00Z

Title: Statistical Analysis of the Amplitude of Radio Waves Reflected from the Ionosphere Authors: Pradhan, S. M.; Srivastava, S. K.; Singh, B.; Tantry, B. A. P. Abstract: The influence of travelling ionospheric disturbance (TID) on the probability distributions of the amplitudes and the difference between the successive amplitudes of radio waves (v_τ) separated by equal time intervals (τ) has been investigated. It is shown that the varying contribution of the steady-to-random component in the received echo gives rise to different types of basic distributions in the different successive portions of the TID and the combination of such distributions yields different types of distributions including that of the M-type. The probability distribution of v_τ remains unaffected by the presence of specular component and is found to be Gaussian even in the case of M-shaped amplitude probability distribution. The probability distribution of v_τ and the auto-correlation function have been applied to determine the rms value of the random velocity of the irregularities, and the implications of the results are discussed. Finally, the effect of the speed of the TID on the speed of fading is also discussed. Page(s): 230-235

Pattern Function of Semicircular Arc Antenna Array

1972-09-01T00:00:00Z

Title: Pattern Function of Semicircular Arc Antenna Array Authors: Dey, K. K.; Misra, V. C. Abstract: The radiation characteristics of a semicircular arc antenna array have been presented. Expressions for the vertical and the horizontal field patterns have been put either in closed forms or in the form of convergent infinite series for different phase relations between the radiators. A comparative study of different vertical radiation patterns has been made for three different phase conditions between the radiators. Page(s): 227-229

Characteristics of Large Scale Ionospheric Irregularities over Delhi

1972-09-01T00:00:00Z

Title: Characteristics of Large Scale Ionospheric Irregularities over Delhi Authors: Chopra, S. K.; Tyagi, Tuhi Ram; Somayajulu, Y. V. Abstract: The Faraday fading records obtained at Delhi for 40 MHz transmissions from satellite BE-B for the period October 1964 to March 1969 and from satellite BE-C for the period May 1965 to March 1969 have been utilized for studying the characteristics of large scale ionospheric irregularities. To estimate the size of the irregularities, the irregularity height was assumed to be around 350 km based on a previous study, in which Faraday fading records taken simultaneously at Delhi and Kurukshetra were utilized. The present study reveals that: (i) during low solar activity, the frequency of occurrence is small during daytime and high during night-time, while during high solar activity the frequency of occurrence shows no preference; (ii) during low solar activity the horizontal sizes vary from 50 to 700 km, the most common size being about 175 km, while during high solar activity, the sizes vary from 5 to 300 km, the most common size being about 25 km; and (iii) the electron content of the irregularities varies from 1.0 x 10¹³ to 1.3 x 10¹⁶ m^-2 being 0.1 to 35% of the background electron content during low solar activity and from 4 x 10¹⁴ to 1.2 x 10¹⁶ m^-2, being 0,03 to 12% of the background content during high solar activity. Page(s): 224-226