Dr. Supratik Sanatani, VU3IFB
It was an odd combination of fixtures which greeted us as we entered AIR Kolkata transmitting station at Amtala. There was a table tennis table laid out in front of the retired Westinghouse transmitter panels. This transmitter was already decommissioned and we could locate the number plate tucked away at one corner “ 2.5 kW Westinghouse May 1948 DWG NAA11560 So FEZ65900 Westinghouse NP 2145413”. This building had two wings, the one on the left housed the 100 kw MW transmitter and the one on the right housed the 50 kW shortwave transmitter. Soon the Westinghouse transmitter would give way to equipment for DRM simulcast on existing AIR Kolkata frequencies. The bulk of the DRM equipment would be voltage stabilizers and power supplies which would be housed here. In future we would see neither the table tennis table nor the Westinghouse transmitters!
We arrived while the shortwave transmitter was off the air between morning and afternoon transmissions. This window allowed the helpful engineer to take us on a tour of the transmitter facilities. The water cooled valves gave us a peek into the complexities of handling high power. The power supply area was at the back of the transmitter room which housed large transformers. I could locate at the back of the transmitter the serial no 016 for this BEL HMB 144 make transmitter of year 90-91. In the front panel a number of typed sheets displayed the operating instructions and one paper had the new frequency schedules written on it in pencil where 4820 kHz had replaced 7210 kHz for the 0230- 0410 UTC broadcast. At 0720 UTC the carrier with pure tone was switched on. The frequency counter showed 7.2099982 kHz. Fixed on the front panel was a Sony ICF7600 receiver for monitoring purposes. The change of frequency was through motorized devises attached to thick copper coils. The output power was 40 kw as displayed by the panel instruments.
The medium wave transmitter was located on the left half of the building. This was a BEL HMV 140 transmitter serial no 003 but was presently non functioning. Ever since the 120 m antenna mast connected to this mw transmitter collapsed, transmission had been going on from a 2×10 kW mobile transmitter made by the Croatian company RIZ. The mobile transmitter came in two neat containerized units which were placed at the back of the transmitter building. One container was the power supply and the other one was the transmitter unit control panels and even a crammed up quarter for the personnel. The antenna which came with this unit was commissioned close to the place where the former antenna mast had collapsed in May. The new mast is smaller in height, has a loading hat on top and rhombic elements all around. The older antenna mast had a large room housing the antenna tuning unit at its base. The new antenna had a smaller antenna tuning enclosure. The new Riz transmitter is DRM capable and preparations are under way for DRM simulcast. They were waiting for the new power supply transformers to be installed. Brisk civil construction was already under way.
The antenna field at the back of the transmitter building had the MW mast to the left and the dipoles for the shortwave transmitter to the right. There were two dipoles, one for the 41 mb and other for the 60 mb. To us DXers they were of special interest. The antennas were oriented south southwest. They were suspended from huge towers, for antenna impedance adjustment, the dipoles could be lowered or raised.I guess the height of the antenna also determined its firing angle. No wonder that Kolkata 4820 kHz at 1800 UTC which struggles under China Lhasa at South Kolkata was loud and clear Goa in west coast of India. We were at the Amtala site and from there we could see the Chandi site at distance some 500 m away southwest on the same Baruipur Amtala road. It is the Chandi site which houses the legendary Kolkata A transmitters .
At Chandi transmitter site we were greeted by a huge dish antenna for down linking signals from AIR studios at Eden Gardens Kolkata. The transmitter building had a FM antenna on top for studio link. Besides these two studio links there was a E2T2 cable link as well as a telephone link through BSNL cables. The Chandi site used the satellite link while Amtala site used the E2T2 link. Both of the sites had very rudimentary studio facilities for playing taped fillers in the event of all link failure from the studios. They were seldom needed nowadays while in the past, during the days of telephone link only, it was no unusual for us to listen to filler music during periods of link failure.
The main building had two parts. The left part housed two 100 kw transmitters running in tandem for 657 kHz Kolkata A. This is the prime radio channel in the whole of this region and one of the oldest. Living up to its reputation, the 100 kw transmitters were running close to 120 kw. The right hand part of the building had the 1323 kHz commercial broadcast transmitter with 20 kW. The technical persons were divided to both part of the building. Apart from us there were another set of visitors – trainees from engineering colleges. They were, however, sulking because they had sit in one part of the building where the ac was malfunctioning. In contrast we were overjoyed that a helpful engineer was taking us through a guided tour of the iconic radio station – something most Bengalis of this part of the world have grown up to be familiar with.
The feeder lines were coaxial fashioned out of a set of copper rods arranged in one inner ring and another outer ring. The outer ring was grounded and was therefore the “shield” The inner ring was the active element. The desired feed line impedance could be obtained by arranging the elements in desired number and desired distribution. Supported on insulators and poles these coaxial distribution of elements ran out to the antenna field to the antenna tuning unit which was housed in an enclosed building at the base of the 120 m antenna mast. That was far cry from the RG 58 coax and a small box of antenna tuning unit we DXers are familiar with.
As we returned to the main transmitter building to take leave, it was late afternoon and through the transmitter monitors we could hear the unmistakable opening tune of the popular women’s programme – “ Mahila Mahal”. I wonder if the helpful Engineer realized how much this visit meant to us DXers, some of whom have been tinkering with the radio dials for close to 45 years. As young boys we woke up to the signature tune from these transmitters, as hobbyists we saw the tubes , transistors, jammers , DTH and SDR’s and now we are here to see the AIR DRM compatible transmitters coming while so many broadcasters such as DW and Radio Nederland are closing shop.
Dr Supratik Sanatani reports after visiting Amtala and Chandi in July 2012 with three other IDXCI members Babul Gupta, Sudipta Ghosh and Swopan Chakraborty
Photo’s courtesy www.riz.hr