bright antennae bristle with the energy

GeorgeC

GeorgeC

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GeorgeC
So it begins. There's a STEM event at school next weekend, so I made a crystal radio. It's For The Children(tm).

The form was made from a 48" long pine 1x4, cut in half, notched, with slots hacksawed in the ends with 1/4" spacing. 10 turns of 24awg magnet wire was sufficient to make an indoor loop antenna. I used a BAT41 Schottky diode as the detector and a set of Brandes Superior Matched Tone headphones from 105 years ago. It sounds great!

crystalset2.jpg

selected bibiography:

https://www.nutsvolts.com/magazine/article/remembering-the-crystal-radio
https://earmark.net/gesr/loop/
https://aa7ee.wordpress.com/2025/06/17/a-crystal-set-with-no-external-antenna/
https://forum.digikey.com/t/substitution-for-the-1n34a-diode-for-crystal-radios/43366
https://hobbytech.com/high-perf-tips
https://mikeselectronicparts.com/product/solderless-crystal-radio-kit-5/
https://analogdial.com/PO-101/PO-101.html
http://www.thelen.us/1crystal.php
https://www.4mcveys.net/2018/10/05/a-very-efficient-loop-antenna-for-am-broadcasts/
http://www.networxcomputer.net/amloop.html
https://www.lwca.net/library/articles/ywk/looptheo.htm
 
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I made one of those when I was 8, thought it was great fun.
 
Might be fun to try using an oxidized razor blade in place of the diode.
 
As a kid, I remember having a Radio Shack N-in-1 kit; my dad and I built a shortwave radio with the included prewound ferrite coil. It's more fun when you have a nanovna and an oscilloscope...

I started playing with meshtastic as well. Kinda neat, but not quite useful in an urban environment.
 
Similar here. I had a kit for a crystal radio that dad helped me assemble. Dad strung an antenna wire from the house to a telephone pole out at the street. The radio worked pretty well, especially at night.
 
Great build, but I can't help myself - the plural for radio antenna is antennas.
Antenae only applies to bugs (of the biological kind).

Also, call the radio station and ask them to play this during your demonstration (or set-up your own AM transmitter):
 
The STEM event was great! Kids and adults alike were amazed that it did not require an external power source.

This one could only get the top half of the AM band. The next one will be larger in area and with more turns of wire. The Litz wire juice is probably not worth the squeeze. I may try a separate pickup coil so I can more easily control how much the diode loads down the antenna loop.

GeorgeC said:
I started playing with meshtastic as well. Kinda neat, but not quite useful in an urban environment.
Click to expand...
Meshcore seems more suitable.
 
GeorgeC said:
The STEM event was great! Kids and adults alike were amazed that it did not require an external power source.
...
The next one will be larger in area and with more turns of wire. The Litz wire juice is probably not worth the squeeze. I may try a separate pickup coil so I can more easily control how much the diode loads down the antenna loop.
Click to expand...
I was invited to do an encore doubleheader for the 3rd grade science classes.

I switched to Litz wire and added an impedance matching transformer.

I did some experiments with a spiral wound antenna on a 3' frame. The larger aperture helped. I also experimented with tapping the coil, which sometimes dramatically improved performance. I did not have much luck with pickup coils, probably because I was doing it wrong.

crystalset.jpg
 
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