Aerospace and Electronic Systems Magazine March 2017 - 23

Giannetti
at 51.7 kHz (5800 m wavelength) and fed
the continental aerial with a current of 50
A. The refurbished Marconi station was
then used for radiotelegraphic service
with some European cities (Berlin, Moscow, Oslo, Poznan, etc.), still retaining
the call sign ICI. From 1920 to 1923 the
old radio was also equipped with a 6 kW
VLF vacuum-tube transmitter, produced
by Marconi Co. Due to its limited power,
however, it turned out to be unsuited for
long-range continental service and it was
therefore used only for links with Barcelona, Spain. Also an upgrade of the
colonial aerial was planned, but it was
not realized, due to the abovementioned
handover of the Coltano radio center to a
private company in 1924.
The IRN inquired about a location
suited for the installation of a receive
station so as to enable full-duplex radiotelegraphic connections. As a matter
of fact, according to the design criteria
of the 1920s, the receive station had to
be kept at least 20 km away from the
transmitter (i.e., outside the dotted circle
in Figure 13), so as to preserve the receivers from the massive radio frequency interference caused by the transmit
equipments. Being the service mainly
intended for North America, the location of the receive station was chosen
on a line (dashed in Figure 14) that was
Figure 12.
The 250-m high masts of the VLF curtain antenna. Left: sketch of a mast's basement, with sphericalperpendicular to the great circle connectshaped bottom end; right: upside view from the bottom of a mast (from [9]).
ing Coltano to New York [9] and in the
proximity of the sea, where reception
and then gradually raised. The picture in Figure 12 shows one of
was better. Again, the incumbent handover forced the IRN to a
the masts top towering from behind the new radio building, with
straightforward solution, i.e., to temporarily set the receive station
the marshy environment clearly visible in the foreground.
inside the Navy Academy's premises in Leghorn.
The new radio, which got the call sign ICC, became fully opAs planned, in 1924 the Coltano radio center was entrusted to
erational on Apr. 15, 1923, and was operated by the IRN until Dethe privately-owned company Italo Radio which, until 1928, procember 1923, providing intercontinental radiotelegraphic services
vided both continental services (to Prague, Budapest, Bucharest,
between Coltano and fixed points in North America, in East Africa
Sofia, and Belgrade) and intercontinental ones (to North and South
Italian colonies (Massawa and Mogadishu), and in Turkey. In adAmerica, and the Far East) [28]. Furthermore, in the subsequent
dition, the station provided telegraphic service to a limited number
years, the company did some upgrades of the Coltano transmit site,
of ships during their navigation. In this period the overall monthly
under the management of Vittorio Gori, the Director of Italo Ratraffic grew up to about 140,000 charged words per month. For a
dio's Experimental Lab since 1924 [29]. According to [8] in 1926
simple assessment of the station's traffic capacity, assume an averItalo Radio built a new curtain antenna; witnesses refer to four 180
age word length of 10 characters and recall that using a Baudot
m-high masts located in a neighboring field, north of the area occoding 5 bits are sufficient to encode a character. Then the station's
cupied by the Vallauri's large curtain antenna.7
traffic was equivalent to about 7 Mbit/month. Also, for a telegraph
transmission speed of a few tens of words per minute, the equiva7
According to a comprehensive list of radiotelegraphic stations
lent transmission bit rate was in the order of tens of bits per second.
compiled in 1927, i.e., during Italo Radio's management period,
In the early 1920s, in parallel with the construction of the new
Coltano hosted Vallauri's ICC station and two more stations,
radio, Marconi's station (dubbed the "old radio") was upgraded.
with call signs ICM and IDG (see [30, p. 1154]). It is not clear if
The obsolete spark transmitter was dismantled and replaced by a
these call signs refer to some new transmit facility that was built
50 kW Poulsen-type arc converter, made by IRN, which operated
in Coltano by Italo Radio.
MARCH 2017

IEEE A&E SYSTEMS MAGAZINE

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine March 2017