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![](/images/462.jpg) | Coherer Radio Wireless Detector | Coherers predate tubes, magnetic detectors, and crystals as detectors. Their use even predates radio. It was the first detector used for radio reception. In the glass tube there is a very small opening between the two metal plugs; in that opening there are metal filings. When a radio signal is received, the filing clump together. The door bell (minus the bell) was used to knock the filings apart after they cohered when a radio signal was received. Here is an experimentor's coherer mounted on a telegraph sounder's base. The patent date on the coil is 1894. I assume this one is from the teens or 20s. |
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