The Marconi Museum

 

Remnants of Marconi's Original Antenna Wires

These wires were found in a pine tree adjacent to the Villa building. It is known that Marconi used this tree for one of his antenna supports, and it is assumed that these wires and egg insulators were those that he used in his original experiments.

 

An early Coherer Receiver

The Coherer is located at the centre front. This particular receiver did not have the mechanical vibrator to "de-coherer" the metal filings after they had stuck together and formed the electric circuit.

The coherer is essentially a switch which "latches" in the presence of an applied high-frequency signal. In some aspects, it's operation may be liken to that of a modern day thyristor. Both the thyristor and the coherer present a high resistance path until latched by an external influence - a dc control current in the case of the thyristor and a high frequency signal of only a fraction of a microwatt in the case of the coherer.

Resetting the Coherer is similar to resetting a thyristor - the thyristor remains latched until the dc control current and the current flow (from anode to cathode) is reduced to zero. The coherer remains "latched" until the rf signal is removed and the metal filings within the coherer are vibrated. In it's latched state the coherer's detecting action is lost.

A later version of the Coherer receiver

The Coherer is the white horizontal tube-like device to the right of the photo. Here the coherer is mounted on a electrical vibrator to "de-coherer" the metal filings in the coherer tube. All Marconi's early receivers used an electric bell to as a sounder. They were constructed to detect the presence of a wireless signal rather than decode it.

The other components within a coherer receiver in addition to the coherer and the vibrator for the coherer, were typically a sounding device, e.g. a bell, and a battery and a sensitive relay to operate the bell. The coherer could not sustain the full operating current taken by the bell or the coherer vibrator.

Circuit Diagram of the Coherer Receiver

The terminals of the coherer "N" are directly connected to the dipole antenna A and A'.

Battery P, the coherer N and relay R are connected as a series circuit via chokes n and n'. The presence of an hf signal causes the coherer to conduct and hence relay R closes. Relay R in turn operates the bell M and the coherer vibrator S.

Diagram of the Coherer

The metal filings are between the two "pole pieces" in the centre of the horizontal tube. The "leg" is where the tube is evacuated.

 

A Display of Receivers

The Coherer can be clearly seen mounted on the electrical vibrator in the receiver in the foreground. The batteries provide power for the bell.

The third receiver from the front is a Rutherford-Marconi Magnetic Detector which was invented in 1902 and rapidly replaced the coherer. The magnetic detector offered considerably improved reliability and sensitivity over that of the coherer and was the mainstay of wireless receivers until about 1914. The rectifying detectors, such as the cat's whisker were relative latecomers on the Wireless scene being invented by B.F. Miessner in 1910.

 

An early Spark Coil Transmitter

 

A typical ship's wireless installation c.1910

 

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Last update 6 Oct 2003