ROCCA di PAPA

IYØORP

ROCCA DI PAPA GEOPHYSICAL OBSERVATORY
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Sez. A.R.I.-FRASCATI Box 44 – 00044 Frascati – ITALY

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On August 11th 1932 Guglielmo Marconi carried out some radio experiments using microwaves from Rocca di Papa  (Rome) to Capo Figari (Aranci Gulf, Sardinia). The Rocca di Papa emitter was installed on the terrace of the Geophysical Observatory (750 meters ASL). Marconi had already carried out some experiments in the Tigullio Gulf during October-November 1931 and again in April 1932 using microwaves modulated by both telephony and telegraphy. These were repeated in greater detail during July-August 1932 between Rocca di Papa and Marconi’s yacht, Elettra, which was steaming towards Aranci Gulf, and finally between Rocca di Papa and Capo Figari (269 km). On August 10 1932 the Elettra  headed on a course joining Rocca di Papa and the Aranci Gulf.

At a distance of 63 km. morse signals were received immediately, around 1:15pm approximately, with maximum readability, and they were similarly maintained  until the power output of Rocca di Papa was insufficient for the distance and conditions involved.  During the whole period previous and successive to sunset, the signals alternated in strength.  At around 10pm the strengthening was evident and at 10:15 approximately, at 193 km distance from Rocca di Papa, meaning double the expected distance from the aforesaid station, the reception turned out optimal. The clear and easily decoded morse signals, were such as to suggest the  possibility of a regular high speed service.  However, at 1:15am approximately at 224 km the signals were hardly perceivable and then disappeared. During the morning of 11.8.1932 the receiving reflector was transported to the face of Capo Figari  (340 mt. ASL) and arranged on the terrace pointing towards  Rocca di Papa. At 4pm approximately on the same day  transmissions began from Rocca di Papa, and, after some adjustment, signals were immediately received in Capo Figari,  although not too strong. Towards 6pm approximately, their intensity increased gradually. The telegraphic signalling turned out clearer and radiotelephony was clear but with intervals. Until 7:20pm approximately usable signals were maintained.

The wind to the face was very strong from the northeast, weather fine, the atmosphere rather humid. The reflector was subject to vibrations, but they did not seem to influence the reception. Towards sunset the usual variations of intensity were noticed;  it appeared to be obvious that with the  disappearance of the solar disc from the horizon,  a strong attenuation of the signals took place After sunset the signals were weaker than during the hours of daylight. From time to time radiotelephony was intelligible and the telegraphic service, although with some difficulty, would have been possible. The experiments had terminated towards the midnight.

The emitter installed at Rocca di Papa, was composed of four  Barkhausen Kurz two valve oscillators, situated directly behind four parabolic reflectors. Measurements proved that each of the oscillators had an output power of 3.8 watt, making the total output approximately 15 watt, to which must be added the gain of the reflectors of around 40 times approximately. The receiver mounted on the Elettra, and subsequently transported to the face of Capo Figari, was equipped with similar valves to those of the emitter, and used  a unique parabolic reflector.

The transmitter and the receiver were enclosed in separate metallic boxes, placed immediately behind their reflectors, side by side, from which exited the pair of wires leading to the hertz dipoles. These dipoles (from two to four for the transmitter and one for the receiver) had a length of approximately 12 cm. and were arranged horizontally several centimeters along the focal line of the parabolic cylinder reflector. The necessary power plants for supplying  the valves were situated at a distance from the reflector and connected using packs of flexible conductors.

With thanks to the  ROCCA DI PAPA GEOPHYSICAL OBSERVATORY and Aldo, IØDJV for the above text (edited by the Webmaster)