Page 123 - The Secret War in the Italian front in WWI (1915-1918)

CHAPTER SIX

6.10 Guglielmo Marconi visiting Treviso radio station in 1916 (ISCAG Archive)

hundreds of kilometres of distance, so that the necessary high-power radiations would reach also
the enemy’s rear. The regulation of transmitted power at levels suitable for different applications,
became gradually widespread during the war, but, at the same time, receiver sensitivity became
stronger thanks to the introduction of vacuum tubes that made it possible to detect weaker and
weaker signals, requiring larger efforts to elude interception.
A frequent change of the transmission wavelength could limit the enemy eavesdropping
opportunities. Some Italian radio stations had used this method in the period before the war, by
changing the wavelength with no fixed rule . In the same period, fixed stations of the Austro-
23
Hungarian navy implemented the wavelength changing method shown in picture 6.11, with
transmission wavelengths between 300 and 3,000 metres . The changes had to be frequent to
24
prevent interceptors from identifying the programmed sequences.
However, as discussed further on, technologies then available allowed only few radio channels
to be allocated on the limited frequency band available for field communications. Moreover,
frequency changes were not easy to perform, especially on the land front, where many friendly
and enemy transmissions crowded the same radio channel .
25
Conversely, reducing the duration of communications proved to be quite effective, especially when
the enemy was not prepared to intercept because, for instance, it could not predict the frequency that
would be used. In order to neutralize this kind of contermeasure, the eavesdropping organizations

23 Specialist Battalion of the Engineer Corps, Radio Office, Intralcio dell’intercettazione dei radiotelegrammi, (Disturbance
of radio telegram interception) 6 April 1913. There had been tests with frequency changes one or several times during the
message transmission, a technique currently called frequency hopping,
24 Office of the Chief of Navy Staff, Intelligence Office, Memorandum no. 27: AUSTRIA, Sistema di segnalazioni
Radiotelegrafiche (AUSTRIA, radio telegraphic signals warning system), 1 March 1913, AUSSME, Series F4 Services
office, env.7.
25 On the other hand, the transmitters could be tuned to very few channels or only to one channel.

121