The untold story of what was once the most powerful radio station of the world


History – (by Prof.Filippo GiannettiUniversity of Pisa, Italy)

In late 1902, Guglielmo Marconi decided to build an “ultra-powerful”; radiotelegraphic station in Italy, providing intercontinental connections with the Americas and the Italian colonies in East Africa. This was the first ultra-powerful station in Marconi's home country and one of the first in the world, too. As matter of fact, at this time there were only three operational ultra-powerful stations: one in Britain, one in the U.S. and one in Canada. Coltano, a flat, swampy and scarcely populated rural area about 10 km south of Pisa, was the selected site due to a number of favorable factors.

 The wet soil has a high electrical conductivity, which eases the radiation of ground waves.

 Coltano is located located almost halfway from Rome, Italy’s capital, and Milan, Italy’s main industrial city,

near the Tyrrhenian Sea’s shoreline, in a very favorable position for communications with Italian colonies in Africa and with the Americas.

 Nearby cities, Pisa and Leghorn, have good connections with the rest of the country, by road, railway and telegraph lines.

 Coltano area was an estate of the King of Italy, Vittorio Emanuele III, who enthusiastically agreed to make it available for Marconi’s project.

The design included a main building in Tuscan style, which was to host the transmitter together with the relevant control equipment, and a couple of long horizontal-wire antennas: one for links with North America and one for East Africa. The construction started in 1905, but the work proceeded at slow pace, mainly due to the harsh and wet environment that caused the station's wooden roof to rot and metal structures to rust.

“Palazzina Marconi”, (Marconi’s House)

This also impaired the stability of the high antenna towers. The building, named; “Palazzina Marconi”, (Marconi’s House), was eventually completed in October 1910, while the whole station was ready in November 1911. The Palazzina Marconi hosted an asynchronous rotary spark gap transmitter, like that available in the Clifden station (Ireland), operating at 43 kHz (7000 m wavelength), and fed two bent antennas. Each antenna extended over 530 m and had 4 pairs of 75 m-high towers with transversal riggings that suspended 24 horizontal parallel wires. The power consumption of the station was about 300 kW, while the transmit power is estimated to be 14 kW, thus yielding an efficiency lower than 5%.

On November 19, 1911, in the presence of the King, Marconi successfully inaugurated the station by sending a telegram to the Director of the New York Times. The message was transmitted from Coltano to Glace Bay (Canada), 5360 km away, and was relayed to New York via land lines. Another telegram was sent to Clifden (Ireland), 1850 km away, and a further telegram was sent to the newly-built Italian colonial station in Massawa (Eritrea), 4160 km away. With this maiden transmission, the Coltano station set some remarkable records:

 it was the first intercontinental radiotelegraphic station in Italy;

 it was the most powerful station in the world;

 transmission from Coltano to Glace Bay set the new distance record for wireless communications: 5360 km;

 the distance between the furthest points at which the signals could be received (i.e., 10720 km) was more than one-fourth of the Earth circumference, corresponding to the coverage of one-sixth of the Earth surface);

 the transmission from Coltano to Massawa went through more than 2000 km of Sahara and was the first across a desert, proving wrong the belief that ground wave propagation is impossible over dry and poorly conductive soil.

In 1920-1923, the Italian Navy built a new radio station for trans-continental service with North America, designed by prof. Giancarlo Vallauri, a prominent scientist and director of Navy's Electrotechnical and Radiotelegraphic Institute, based in the nearby city of Leghorn. The new radio consisted of a main building which hosted the transmit and control equipment, and a huge curtain-type antenna, besides some subsidiary buildings for the accommodation of the personnel in service at the station.

The station was equipped with a couple of more modern transmitters: a 250 kW transmitter based on a Béthenod–Latour alternator, and a 350 kW transmitter, featuring two static Poulsen converters. Any of the two transmitters had nominal frequency 18.750 kHz (16,000 m wavelength) and could be selected to feed the huge curtain-antenna, having a square base with 420 m-long sides, supported by four masts; each one was 250-meter high. The antenna’s pavillon consisted of a net of phosphorous-bronze wires 3.4 mm thick and spaced about 15 m apart from each other.

Guglielmo Marconi

The net was reinforced with steel cables for the outer wires, yielding a total weight of about 4 tons. The new radio provided intercontinental radiotelegraphic services between Coltano and fixed points in North America, in East Africa Italian colonies (Massawa and Mogadishu) and in Turkey. In addition, the station provided telegraphic service to a limited number of ships during their navigation.

From 1924 to 1928 the management of the new station (referred to as the "new radio") was entrusted to the private company Italo Radio, which provided both continental and intercontinental ones radiotelegraphic services. In 1929, the site of Coltano came under the direct management of the Post and Telegraph Ministry which decided to upgrade the transmit equipment from long- to short-waves (SW) for long-range service to merchant ships.

The station was renewed under the technical supervision of the admirals Gino Montefinale and Giuseppe Pession, two qualified Navy’s scientists. Vacuum-tube transmit equipments were installed in  Coltano for both oceanic and coastal service and a SW antenna was erected. This consisted of 4 omnidirectional Franklin-type vertical aerials, one for each frequency of the main service, hanging from a 180 m-long horizontal rigging, suspended between two 60 m-high towers. The SW transmitters were activated on July 1st, 1930, and ensured long-range radiotelegraphic service to merchant ships.

The most spectacular event of this period happened on October 12, 1931, on the occasion of the 439th anniversary of the discovery of America. That day, Guglielmo Marconi, from his office in Rome, remotely switched-on the lights of the great statue of Christ the Redeemer in Rio de Janeiro, Brazil, 9200 km away.

Marconi pressed a key that sent the command via landline to Coltano, then, a 2 kW SW transmitter sent a signal to a radio station in Rio. There, the command was eventually transferred via landline to the flood- lighting switchgear, on the Corcovado Mountain.

In late 1931 the main SW transmitters were upgraded by adding amplitude modulation functionality, which enabled radiotelephonic service, too. For almost a decade (1930÷1940), Coltano was the key Italian (and one of the main European) long-range radiotelegraphic and radiotelephonic station providing wireless connections with both ships and fixed points all around the globe. Since 1932 regular public connections were held with the Italian concession in Tianjin, China, 8250 km away. In the same year, the first public service from land to vessels was activated.

map of Coltano station

The first served ship was the Italian liner Conte Rosso which kept regular contact with Coltano while sailing to Shangai, 9200 km away. The service was soon extended to the Rex and the Conte di Savoia liners, sailing to New York, 6650 km away, and to the Duilio and the Giulio Cesare liners, sailing to Cape Town, South Africa, 8670 km away. In 1935, two new shortwave transmitters, supplied by Marconi Wireless Co., were installed: a 56 kW transmitter for radiotelegraphic services and a 35 kW transmitter for radiotelephonic services.

During WWII, on June 14, 1944, withdrawing German troops blew up the building of the new radio and all the antenna towers of the radio center. The building of the old Marconi station, which had not been operated for a long time, was instead spared. After the war, the radio center of Coltano was finally abandoned. From 1955 to 2008, a U.S. military radio site was set in the proximity of the old radio center. Since 1952, Coltano hosts a MW transmit site of the Italian public broadcasting company RAI. Also, the Pisa section of the Italian Amateur Radio Association (A.R.I.) occasionally operates a commemorative radio station (callsign IY5PIS) from Coltano.

Today, the only remaining vestiges of the historic radio center are the concrete basements of the great antenna towers, a few small portions of brick walls of the new radio building, the quarters of the service staff and the Palazzina Marconi of the old radio. The latter is the most important relic surviving WWII’s devastation. Unfortunately, it badly suffered the effect of time and, currently, this historic building is in disrepair.