Marconi's law
Encyclopedia
Marconi's law is the relation between height of antennae
and maximum signalling distance. Guglielmo Marconi
enunciated at one time an empirical law that, for simple vertical sending and receiving antennae of equal height, the maximum working telegraphic distance varied as the square of the height of the antenna. It has been stated that the rule was tested in experiments made on Salisbury Plain
in 1897. Also by experiments made by Italian naval officers on behalf of the Royal Italian Navy in 1900 and 1901. Captain
Quintino Bonomo gave a report of these experiments in an official report.
where c is some constant.
Marconi's law can be deduced theoretically as follows:
The above law is, however, much interfered with by the nature of the surface over which the propagation takes place.
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
and maximum signalling distance. Guglielmo Marconi
Guglielmo Marconi
Guglielmo Marconi was an Italian inventor, known as the father of long distance radio transmission and for his development of Marconi's law and a radio telegraph system. Marconi is often credited as the inventor of radio, and indeed he shared the 1909 Nobel Prize in Physics with Karl Ferdinand...
enunciated at one time an empirical law that, for simple vertical sending and receiving antennae of equal height, the maximum working telegraphic distance varied as the square of the height of the antenna. It has been stated that the rule was tested in experiments made on Salisbury Plain
Salisbury Plain
Salisbury Plain is a chalk plateau in central southern England covering . It is part of the Southern England Chalk Formation and largely lies within the county of Wiltshire, with a little in Hampshire. The plain is famous for its rich archaeology, including Stonehenge, one of England's best known...
in 1897. Also by experiments made by Italian naval officers on behalf of the Royal Italian Navy in 1900 and 1901. Captain
Captain (nautical)
A sea captain is a licensed mariner in ultimate command of the vessel. The captain is responsible for its safe and efficient operation, including cargo operations, navigation, crew management and ensuring that the vessel complies with local and international laws, as well as company and flag...
Quintino Bonomo gave a report of these experiments in an official report.
Description
If H is the height of the antennae and D the maximum signalling distance in meters, then we have, according to Marconi's law-
,
where c is some constant.
| c | D | Apparatus |
| 0.17–0.19 | 60 kilometres (37.3 mi) | Marconi's original apparatus |
| 0.15–0.16 | 60 kilometres (37.3 mi) | Same, with longer sending spark |
| 0.12–0.14 | 136 kilometres (84.5 mi) | Marconi's improved apparatus, with jigger in receiver |
| 0.23–0.15 | 143 kilometres (88.9 mi) | The same, but with Italian Navy telephonic receiver |
Marconi's law can be deduced theoretically as follows:
- Hertz has shown that at distances large compared with its length the magnetic force of a linear oscillator varies inversely as the distance.
- The maximum value of the current set up in any given receiving antenna varies as its length, also as the magnetic force of the waves incident on it, and as the maximum value of the current in the transmitting antenna.
- Hence, if the magnetic force of the waves incident on a receiving antenna of height and if the distance between the sending and receiving antenna, and if the maximum values of the currents in the sending and receiving antenna, we have various charging voltage of the current in the sending antenna which varies very nearly as its capacity — that is, as its height — and if the sending antenna has the same height as the receiving aerial, we have some constant.
- For any given receiving apparatus a certain constant minimum value of the maximum current in the receiving antenna is necessary to cause a signal.
- Therefore it follows that, with given receiving and sending apparatus, we must have a constant.
- That is, the maximum signalling distance with given apparatus will vary as the square of the height of the antenna.
The above law is, however, much interfered with by the nature of the surface over which the propagation takes place.
See also
- ArcoGeorg von ArcoGeorg Wilhelm Alexander Hans Graf von Arco was a German physicist, radio pioneer, and one of the joint founders of the "Society for Wireless Telegraphy" which became the Telefunken company. He was an engineer and the technical director of Telefunken...
-SlabyAdolf SlabyAdolf Karl Heinrich Slaby was a German wireless pioneer and the first Professor of electro-technology at the Technical University of Berlin .-Education:Slaby was born in Berlin, the son of a bookbinder...
(TelefunkenTelefunkenTelefunken is a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the Allgemeine Elektricitäts-Gesellschaft...
) - Electrical lengtheningElectrical lengtheningElectrical lengthening is the modification of an aerial which is shorter than a whole-number multiple of a quarter of the radiated wavelength, by means of a suitable electronic device, without changing the physical length of the aerial, in such a way that it corresponds electrically to the next...