http://obsoleteskills.wikispot.org/Crystal_set_radiosRecent Changes of the page "Crystal set radios" on Obsolete Skills Wiki.en-us http://obsoleteskills.wikispot.org/Crystal_set_radios2008-03-09 01:20:14 <div id="content" class="wikipage content"> Differences for Crystal set radios<p><strong></strong></p><table> <tr> <td> <span> Deletions are marked with - . </span> </td> <td> <span> Additions are marked with +. </span> </td> </tr> <tr> <td> Line 1: </td> <td> Line 1: </td> </tr> <tr> <td> </td> <td> <span>+ ||&lt;bgcolor='#E0E0FF'&gt;'''Field'''||<br> + || radio, electronics ||<br> + ||&lt;bgcolor='#E0E0FF'&gt;'''Went Obsolete'''||<br> + || Generally, about the 1930s, when ||<br> + ||&lt;bgcolor='#E0E0FF'&gt;'''Made Obsolete By'''||<br> + || Tube radio sets ||<br> + ||&lt;bgcolor='#E0E0FF'&gt;'''Knowledge Assumed'''||<br> + || Basics of radio transmission ||<br> + ||&lt;bgcolor='#E0E0FF'&gt;'''When useful'''||<br> + || When you need to listen to radio broadcasts using no power. ||<br> + <br> + Commercial radio broadcasting began in the US in 1920. Commercially manufactured radio sets were expensive, and many people built "crystal sets" out of readily available materials.<br> + <br> + A crystal set radio consists of a very simple coil and capacitor tuner, a rectifier and a set of headphones. In early homemade versions, the antenna served as the capacitive element, and people wound their own tuning coils. The crystal set required no power - the rectified signal from a sufficiently powerful AM transmitter could drive headphones at enough volume that you could hear it.<br> + <br> + In early crystal sets the rectifier (or "detector") was a natural mineral crystal (commonly galena) with a thin wire called a "cat's whisker" which lightly touched the crystal, and actually formed a primitive semiconductor junction. This device was inherently unstable, and the operator had to continually adjust it to find a good spot on the crystal, and obtain the right touch with the wire. It took some practice to be able to do it consistently.<br> + <br> + Thus, we have two skills - building the thing, and adjusting the cat's whisker to be able to use it.<br> + <br> + If you wish to build a modern version, you will probably use a germanium diode instead of the crystal (around $0.20 each, but you'll probably have to buy a pack of them for a couple bucks). Of course, I suppose this is no longer a "crystal" set, but the name persists.<br> + <br> + == Other references ==<br> + <br> + A (commercially made) crystal set from 1925:<br> + <br> + http://earlywireless.com/gecophone_junior_picinfo.htm<br> + <br> + A modern version with a coil wound on an oatmeal box, a variable capacitor and a germanium diode:<br> + <br> + http://www.streettech.com/archives_DIY/crystalSet.html<br> + <br> + * list other references about this skill here<br> + <br> + [[Comments]]</span> </td> </tr> </table> </div>