AIR KOLKATA ANTENNA TALES

 Dr.Supratik Sanatani, VU3IFB

The super cyclone of October 1999 brought down the antenna 120 m mast of Kolkata A 657 Khz which radiated 2x 100 kw. In the words of an engineer manning the transmitter " we got a phone call that AIR Kolkata A was not audible. When we looked out, the main antenna mast simply was not there !! "The huge mast built of thick gauge metal can still be seen lying in the premises. Portions have been sawed off to make way to the newly installed 120 m mast. This incident caused disruption of Kolkata A transmissions for few days. Transmission resumed only when a new mast was put up.

The new main radiating mast of Kolkata A had a parasitic mast put up few meters down south. It was to act as a reflector and direct most of the radio signals to the north which is the populated part of the State. The southern parasitic mast was to avoid valuable signals getting lost in the Bay of Bengal to the south which is sparsely populated anyway. However, a controversy cropped up in 2011. During a tropical cyclone in July 2011 few fishermen who had ventured out to the sea were lost. There was hue and cry in the media that the disaster could have been avoided if the weather bulletins from AIR Kolkata could be better heard (http://groups.yahoo.com/group/bangladx/message/2668). The AIR authorities were under pressure when news reports originating from the fishing town of Kakdwip said that Bangladesh Betar weather bulletins were better received over the Bay of Bengal ((http://groups.yahoo.com/group/bangladx/message/2686). The AIR authorities woke up and an engineer was dispatched in a coast guard vessel to measure signal strength of AIR transmissions almost 300 km deep down south in the Bay of Bengal. He found good to strong signals all throughout the test area. However, the authorities decided to disconnect the parasitic reflector mast to put the controversy to rest. The parasitic mast still stands up mournfully though in the antenna field of Chandi some 24 km south of Kolkata.

As if this was not enough, the 120 m mast of Kolkata B snapped in May 2012. This was not due to any cyclone or gale. It was presumed that one of the guy ropes anchoring the mast that snapped and that caused a disbalance. This in turn caused a cascading effect and finally the main mast snapped. AIR Kolkata B 100 kw transmitting on 1008 kHz was disrupted for almost 20 days while a new mast, somewhat shorter in height was put up. This new mast has a loading hat on top and rhombic elements on all sides. Presently this is fed by 10 kw standby brand new RIZ mobile transmitter which is running at 8 kW because one part of the panel is not working and the engineers conversant with BEL transmitters would not risk tinkering with the malfunctioning panel of Riz mobile transmitters which is in the warranty period. They would rather wait for the authorized technicians of Riz transmitters to arrive.

Pilferage is another minor irritation which bugs the antenna fields of Chandi. Even though manned by security guards round the clock,and watch towers in the periphery the precious copper of antenna and feeder elements are prey to the thieves. Most often the pilferages would be minor e.g. one coil of some hundreds of tank circuits in the antenna support wires or few lengths of concentric feeder lines. However, these would disbalance the fine tuning required for that extra last mile for the radio signal !

Yet another element which upsetting the fine tuning is the collapsed old tower which is awaiting bureaucratic clearance for disposal . A mammoth steel structure in the antenna fields is bound to add some inductance here or there and compromise design efficiency. The same applies to the disconnected parasitic antenna mast in the south which is still there completete with the ground radials. This is bound to compromise the design efficiency.

The Engineers at the site were however very upbeat. They are proud that their signals were getting around in spite of all the difficulties and they have faithful listeners tuning in. One engineer who had just completed a stint at Orissa talked about a 90 year old faithful listener who would telephone the station at the slightest fall in transmission quality. However, he would also sympathise with the ground realtites. Talking about ground realities in India, I was reminded of the Engineer at AIR Aligarh HPT who talked about Neel Gai's (http://en.wikipedia.org/wiki/Nilgai) charging into antenna curtains and disrupting transmission.

Report by Dr Supratik Sanatani after a visit to Amtala and Chandi facilities of AIR Kolkata along with Babul Gupta, Sudipta Ghosh & Swopan Chakraborty in July 2012.