The Warsaw radio mast () was a radio mast located near Gąbin, Poland, and was the world's tallest structure at 646.30 m (2,120 ft) from 1974 until its collapse on 8 August 1991. The mast was designed with extreme height to broadcast Polish state media around the world, including to parts of Canada and the United States, and even reaching Antarctica. The official name of the facility was Radiofoniczny Ośrodek Nadawczy w Konstantynowie (Radiophonic Transmission Centre Konstantynów), Radiowe Centrum Nadawcze w Konstantynowie (Radio Transmission Centre Konstantynów; RCN Konstantynów) or Warszawska Radiostacja Centralna (WRC) w Gąbinie (Warsaw Central Radio Station Gąbin). It broadcast Polskie Radio's Program I (unofficially referred to as "Jedynka").
Designed by Jan Polak, its construction started with earthworks for the foundations on 5 July 1969, while construction of the tower itself began on 18 October 1972 with a ceremony, and was completed on 18 May 1974. Its transmitter, whose installation started in October 1973, entered regular service on 22July 1974. The opening of the mast was met with extensive celebration and was covered by the Polish Film Chronicle. The tower was used by Warsaw Radio-Television (Centrum Radiowo-Telewizyjne) for radio broadcasting on a frequency of AM-LW (longwave) 227 kHz before 1 February 1988 and 225 kHz (1332 metres) afterwards. Its base was above sea level. Because it had a potential difference of 120 kV during operation, it stood on a insulator. It operated as a mast radiator (half-wave radiator), so its height was half of its 1332-metre broadcasting wavelength. The signals from its 2 MW transmitters could be received across essentially the entire globe. The structure's weight was debated, with some Polish sources claiming it weighed .
Upon its construction, it surpassed the height of the then-tallest structure in the world, the KVLY-TV mast in Blanchard, North Dakota, United States. Following its collapse, the KVLY-TV mast once again became the tallest structure in the world until 2009. After 1991, the tallest structure in Poland has been the FM- and TV-mast Kosztowy, tall. As of , it was the third-tallest artificial structure ever built, after the Burj Khalifa tower in the United Arab Emirates in 2009, and Merdeka 118 tower in Malaysia in 2022.
Construction The mast's location, which was finalised to be in Gąbin, was chosen because of its high soil conductivity and the need for a position in the centre of Poland. A large amount of research was used to decide where to build the mast, which included factors such as soil resistance, ownership of property, and the quality of infrastructure (especially roads).
The mast was initially constructed to replace the Raszyn radio transmitter, which had been constructed in 1931 and rebuilt in 1949. The Raszyn transmitter was designed to cover the Eastern Borderlands, and so Polish authorities did not consider reception in the Recovered Territories. When it became evident that Raszyn could not provide coverage to the entire country, the station received an increase of power to 500 kW, but this too failed. In the late 1960s it was decided to construct a new central transmitter at the geographical centre of Poland (post-WWII borders). Gąbin was chosen not only due to its central position, but also its high soil conductivity. During storms, when the mast could not operate, the signal would be temporarily switched to Raszyn, a process that was eased thanks to direct phone lines from RCN Konstantynów to both Raszyn and the energy sector.
The Warsaw radio mast was a guyed steel lattice mast of equilateral triangular cross section, with a face width of . The vertical steel tubes forming the structures of the mast had a diameter of 245 millimetres (10 in); the thickness of the walls of these tubes varied between 8–34 mm (0.31–1.33 in) depending on height. The mast consisted of 86 sections, each of which had a length of . The mast had 3 arrays of guy wires, each array attached to the mast at 5 levels: , , , , and above ground. Each guy was fixed on a separate anchor block at the ground and was in diameter. To prevent the guy wires from interfering with the radio transmissions, the guys were insulated at regular intervals. The weight of guys and insulators used to anchor the mast was . An elevator and separate protected ladders were installed in the interior of the mast to facilitate access to the various mast components, including the aircraft warning lamps. The elevator was designed by , a Swedish company, and took 45 minutes to reach the top. The lift was nicknamed "Alimak", as a nod to the company that designed it. Safety was a priority, so "Alimak" was provided with an emergency stop function, but no incidents occurred that might have required it. A maximum of 3 people could ride up the elevator, although sources claim 3 people would have felt crowded. The elevator was powered by an internal combustion engine. An area for maintenance supplies was present, in order to transport materials such as lightbulbs for the aircraft warning lights. Inspection crews travelled up it once per month to replace light bulbs, and to watch for cracks in the steel. If a crack was found, the transmitters were turned off and the Raszyn radio mast took over the broadcast. Any cracks were then fixed by welders from Mostostal Zabrze by patching them with sheet metal.
In the lower half of the mast, there was a vertical steel tube, attached to the mast's outer structure with large insulators. This tube was grounded at the bottom, and connected electrically to the mast structure by an adjustable metal bar at a height of when the tower transmitted on 227 kHz longwave and at a height of when it switched to 225 kHz on 1 February 1988. This technique allowed adjusting the impedance of the mast for the transmitter and worked by applying a direct current ground at a point of low radio frequency voltage, to conduct static charge to ground without diminishing the radio energy. Static electrical charge can build up to high values, even at times of no thunderstorm activity, when such tall structures are insulated from ground. Use of this technique provides better lightning protection than using just a spark gap at the mast base, as it is standard at most mast radiators insulated against ground.
The mast was equipped in 16 levels with arrays of six air traffic warning lights with 200 W power. At the top there was a flashing beacon consisting of two lamps of 1,000 W.
A long special overhead radio frequency transmission line of 120 ohms was used to transfer the signal from the transmitter building to the mast. Featuring an asymmetrical coaxial power supply, it consisted of the inner "hot" core of 24 copper wires connected to a small ring at each post, and each was connected by three insulated cables to the outer ring. The outer ring served as the support of another set of 24 wires, known as the "outer braid." The transmission line was monitored whenever the mast was in operation; at night the line was illuminated with street lights, to prevent trespassers from electrocuting themselves. The transmitter building had a volume of and was approximately from the mast. The transmitter consisted of two 1,000 kW units built by Brown, Boveri & Cie. An atomic clock was used to generate the transmission frequency in order to provide a very accurate, stable signal source which could be used as a frequency standard by anyone within signal range. The transmitters had the ability for each component to be turned on manually or all be started with one button. The transmitters were capable of receiving remote input, but the devices needed to use this were not implemented in Konstanynów. When high-voltage power was switched on, the transmitter was protected by two locked doors and crews were informed by way of illuminating a red lightbulb. This lightbulb was controlled by a photodiode that would additionally flash the lightbulb if a short-circuit in the transmitter was detected.
The station, which had an area of , also had a lattice tower of rectangular cross-section close to the transmitter building. This tower was used to provide a radio link for programme feeds from the studio, which ran from the Palace of Culture and Science, Warsaw via a radio relay tower at Wiejca. At Konstantynów, the signal was focused on a parabolic dish at 30 dB and was captured in a horn antenna at the focal point of the dish. Upon reaching the transmitters, a dehydrator ensured that no condensation occurred. The transmission building used a NEC radio set and the TN60 multiple telephony system. This allowed for 60 telephone lines connected to the Polska Poczta, Telegraf i Telefon fixed-line telephone network to be run off the station but the full possibilities of this system were never used.
To supply power to the station, a 110 kV substation was built. The substation was over-engineered due to the strategic importance of the station as Poland's central transmitter: although the power consumption of the transmitting station was large at an estimated 6,000 kW, the substation was capable of supplying much more. Six small towers were erected around the periphery of the station's grounds in order to support aircraft warning lamps where the guy ropes were located.
Problems Approximately ten years after completion of the mast, inspections revealed structural damage caused by wind-induced oscillations at the mast, the backstay insulators and the guys. Repair work was considered to be expensive and difficult, so replacement of the mast by a stronger construction of the same height was considered; however, this was not carried out due to Poland's worsening economic situation. Repainting was started in 1988, but could not be completed because not enough paint was available. A lack of equipment and training of maintenance teams led to a severe degradation of the mast's condition by the late 1980s. An inspection in May 1989 found that 13 strands of the upper guys had been fractured and, by the time of the collapse of the mast in 1991, seven guy wire insulators had been damaged. Another cause of the structure's deterioration was insufficient knowledge of the strains exerted on structures of such a great height. Additionally, on 23 March 1992, Adam Brzeziński, managing director of Mostostal Zabrze at the time, stated to Dziennik Zachodni that Mostostal should have prepared a technical report before starting construction on the risks faced during repair of a strained mast.
Specifications
General characteristics Weight: 420 tonnes (930,000 lb) Height: 646.38 metres (2,120.67 ft) Coordinates: 52 22 4 N 19 48 9 EWarsaw Radio Mast, Google Maps Frequency: 227 kHz (before February 1988), 225 kHz (after February 1988) Type: Guyed steel lattice mast Designer: Jan Polak
Transmitter Model and Manufacturer: Brown, Boveri & Cie, Brown Boveri SL 61 B3 Power: 1,000 kW (1 MW) Total Power: 2,000 kW (2 MW)
Transmitter building Volume: 17,000 m3 Distance from mast: Method of signal transportation: Overhead Radio Frequency Transmission Line
Elevator Model and Manufacturer: Alimak Maximum Capacity: 3 people Type: Climbing elevator Power supply: Internal combustion engine
Staff The manager of the radio station from 1974 to 1980 was Zygmunt Duczmalewski (died 2016). His successor, Witold Czowgan (1947–2017), served as the manager from 1983 to 1986.
The mast had a total of 30 engineers and technicians. It also had 15 administrative staff. Because a large portion of the staff was recruited from around Poland, a new block of flats was built away in Sochaczew to accommodate the staff. More specialised staff were accommodated in the guest rooms of the transmission building. The facility also had a complement of guards, hired directly by the Ministry of Interior, mainly from the local population of Konstantynów.
Collapse