A unique telecommunication link between India and the USSR  was inaugurated by the Prime Minister of India on 2nd November, 1981. This link works on the principle of propagation of Radio Waves in  the  tropospheric  medium  over  long distances. The station of Overseas Communications Service on  the  Indian  side of this link is located at Chrar-e-Sherief near Srinagar and the station on  the USSR side, near Dushanbe in the Tadzik Republic.

The propagation path between the two places passes over high mountainous terrain for a distance of about 685 kms. The radio beam emitted by the transmitting antenna from each of the terminal stations hits the mountain ridges en route which results in a small portion of the incident energy to be diffracted or bent towards the distant terminal. This is the mechanism of propagation between the two stations for establishing the link.

As the beam  passes through  the troposphere which is the  region  immediately surrounding the earth upto a few kilometers, it is subjected to the inhomogeneities of the atmospheric layers resulting in the dimunition of signal strength. This is compensated by employing frequency and space diversity   techniques. By this process, four  received signals are derived and they are combined by special techniques to obtain  a steady signal which enables reliable, good quality communication to be possible. The station at Chrar-e-Sherief near Srinagar employs two large Parabolic Bill-board Type of Antenna of 30 meters square  dimensions for transmission and reception of the signals. The Electronic Corporation   of India Ltd. (ECIL) designed, fabricated and installed the antenna at Chrar-e-Sherief  and  also  supplied similar  structures  for  the  installation  at Dushanbe. The link operates on 800 MHz/900 MHz Bands, with a transmitted power of 10 KW each on two frequencies either way. The radio equipment has been supplied by the USSR.

The International Link between Dushanbe and Srinagar is extended to Moscow and New Delhi respectively on the national systems of the two countries. The link has a capacity of 12 telephone channels to meet the future traffic requirements. The link has been operating over the past one year and is quite unique as it has demonstrated  how  great  distances of formidable mountainous terrain can be spanned by means of tropospheric techniques.

Indian Posts & Telegraphs Department is happy to issue a commemorative stamp on the first anniversary of the  inauguration  of  the  troposcatter link  between India  and  the  USSR.

Source : Information Folder issued by Indian Posts & Telegraph Department, Government of India