inspired by the illegal remote control car i talked about last weekend, today i decided to build a coherer! (thread)
let's start with an ordinary glass fuse! 
using pliers, i pulled one of the caps off and then yanked out the fuse wire.
let's use a file to make filings! the material is brass.
filings poured in and the fuse capped, we now have a coherer -- i hope.
this is the circuit. tuned LC with the antenna and ground connections, coherer, RF bypass capacitor, and then the light bulb that should light up when the coherer conducts.
aargh, the lamp is always on! the filings are a bit too conductive.
the literature says that you're supposed to wait for the filings to oxidize first for a few hours. 😑
for reading material in the meantime, check out this person's thesis which goes into great detail on the history of this fascinating electrical component. researchgate.net/publication/29…
ok this is shocking, TIL that the discoverer of radio was a music professor, David E. Hughes, who figured it all out 10 years before Heinrich Hertz, but didn't publish because of a snide comment by Sir George Gabriel Stokes.
incidentally, we actually have no idea *why* the coherer even works. once better radio detectors were invented, it was discarded and nobody investigated the phenomenon any further.
lol, here is Thomas Edison's approach for finding alternative materials for the carbon microphone.
this paper is EPIC. the "Goddard" referred to here is the same Robert Goddard who invented modern rocketry! apparently he "played with radio as a hobby" aka sciencest the f* out of it. i am in awe
15GHz !? wow.
this paper should be required reading for electrical engineers. i'm only in 60 pages, and there are over 300 pages to go. 😮
oh yeah here's J. C. Bose. according to our favorite internet encyclopedia, Sir Jagadish Chandra Bose was an Indian polymath, physicist, biologist, biophysicist, botanist and archaeologist, and an early writer of science fiction. 🤯
oh yeah, it works! i'm using a BBQ ignitor as a spark source.
hilariously, my $30 crappy keyboard also detects sparks from the BBQ ignitor. they must not have bothered to test ESD. 😂
resistance is normally pretty high but all over the place. when it coheres the resistance drops to about 200 ohms, sometimes less. it's very finicky.
