What Is the Magnetic Detector?

The Magnetic Detector, also known as "The Maggie" or "Marconi Magnetic Detector," was a short-lived innovation in radio communication that was mostly used for transatlantic communications during a short period at the start of the twentieth century. It was perfected by the Marconi Company in 1902 and did a better job than the coherer at making radio signals more detectable at long ranges. It was soon replaced by crystal receivers and more advanced multi-element vacuum tubes.

Especially popular in maritime applications due to its reliability, The Magnetic Detector was only used for about a decade, mainly by European vessels. The first "Maggie" is said to have been installed in 1903 in the Carlo Alberto, an Italian navy warship. More reliable and sensitive than any of its precursors, the Maggie quickly became popular and soon enjoyed commercial success, which lasted roughly from its invention in 1902 until it was outmoded in 1914.

Although its lifespan was brief, The Magnetic Detector was considered a major advance in radio technology, and it became the standard radio detector on most shipboard receivers that were used during this time, including war vessels. It was also used in many cases as a backup. It was more developed than other earlier magnetic detectors because it was driven by a clockwork motor and stationary coils as opposed to only having a rotating magnet above an unmoving iron band.

One of the technical innovations of the Marconi Magnetic Detector was a seemingly endless iron band that consisted of as many as 70 strands of iron wire which were covered with a layer of silk. This band would pass over two rotating pulleys that were turned by a clockwork-style motor; then the band would pass through a glass tube in which there was a copper coil that functioned as the frequency coil for audio pickup.

Two permanent horseshoe magnets were responsible for magnetizing the long iron band as it moved through the glass tube. Using continuous reverse magnetism, which induced a weak DC current in the coil, a variation or flux could be measured, and this allowed for a translation into sound. The apparatus was connected to a telephone receiver that converted the fluctuations into audio.

Considered a rare antique and a collector's item, the Marconi Magnetic Detector is coveted and sought after by radio collectors around the world, who marvel over it's elegant antique technology. It is considered to be a valuable radio artifact, and older models are sometimes painstakingly restored, which can include cleaning and oiling the old parts, as well as replacing key wire connections, which are sometimes broken at the lug, or the easily broken wire loop that encircles the spools.