
We Rediscover Spark Gap Radio by Accident - peter_d_sherman
https://www.youtube.com/watch?v=9zG_DlxyugQ
======
peter_d_sherman
Related:

[https://en.wikipedia.org/wiki/Coherer](https://en.wikipedia.org/wiki/Coherer)

>"The coherer was a primitive form of radio signal detector used in the first
radio receivers during the wireless telegraphy era at the beginning of the
20th century. Its use in radio was based on the 1890 findings of French
physicist Édouard Branly and adapted by other physicists and inventors over
the next ten years. The device consists of a tube or capsule containing two
electrodes spaced a small distance apart with loose metal filings in the space
between. When a radio frequency signal is applied [PDS: Correction, should
read "in the vicinity"] to the device, the metal particles would cling
together or "cohere",

 _reducing the initial high resistance of the device_ ,

thereby allowing a much greater direct current to flow through it [PDS: Or
some at all, as the video shows]. In a receiver, the current would activate a
bell, or a Morse paper tape recorder to make a record of the received signal.
The metal filings in the coherer remained conductive [PDS: In a low resistance
to DC state] after the signal (pulse) ended so that the coherer had to be
"decohered" by tapping it with a clapper actuated by an electromagnet, each
time a signal was received, thereby restoring the coherer to its original
state."

Anyone see a pattern with coherers?

Don't they seem similar, patternwise, to N-P-N transistors, or P-N-P
transistors?

Except for the following things:

1) Control gate (base) acts on RF, not voltage.

2) Coherer remains conductive even after the RF source is switched off.

It would be interesting if a transistor could be constructed in a similar
manner to a Coherer, that is, if metal filings (well, "metal oxide filings",
because the metal filings are typically exposed to oxygen!) between two other
metals in some configuration -- would yield a working transistor...

Now, I don't know that this could actually be done -- I'm only speculating
aloud... <g>

