Probably not as much as when the widespread use of "ham" radios came into popular use in the early 1900's. Crystal sets utility was mainly limited by their relatively short range of passive reception from strong carrier signals from radio stations. Ham radios, on the other hand, had strong enough carrier waves to be received hundreds of miles away from their source. Even today, ham radios often play a significant role in maintaining emergency communications among first-response providers and public audiences, as was the case in New Orleans during Hurricane Katrina, when large-scale commercial radio stations lost power. Of note, however, was the valuable role that crystal sets played during World War II. Because the German army could detect carrier waves from their source, portable radios were prohibited. Allied troops found that homemade crystal sets known as "foxhole receivers" (made from a coil of wire, a razor blade and a pencil lead) at least allowed troops and civilians to hear (albeit one-sided) communications from the BBC. Their lack of need for external power sources made them valuable during brownouts or when batteries were unavailable. Not to overlook the intangible value of often being the first introduction to electronics for many children, whose developing curiosity may lead to eventual careers in science!
To change the frequency on a radio controller car, you change the crystal in the transmitter and receiver.
fudge
At the Radio Tower.
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crystal and crystal Edit: Ignoring the above nonsense... there is a comprehensive article on Wikipedia (see related link) detailing the components of a crystal radio - and how they work.
The address of the Crystal Falls Museum Society is: Po65, Crystal Falls, MI 49920
The address of the Crystal City Historical Society is: Po Box 654, Crystal City, MO 63019
You must obtain a radio card from the receptionist at the radio tower
The phone number of the Crystal City Historical Society is: 636-586-6269.
The address of the Crystal Lake Historical Society Inc is: Po Box 1151, Crystal Lake, IL 60039-1151
Radio Music Society was created in 2011.
Irish Radio Transmitters Society's motto is 'Amateur Radio in Ireland'.