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Earlier I wrote:
<blockquote cite="mid:48EA2FFE.3060302@cyllene.uwa.edu.au" type="cite">
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... a neon lamp has a V-I region in which it behaves as a
negative
resistance - and a neon lamp can therefore be used as an amplifier or
configured as an oscillator.<br>
</blockquote>
I think I was mistaken to suggest that a negative resistance allows one
to make an amplifier - I can't work out how to do it as there seems no
way to provide current or voltage isolation of the input from the
output with only two terminals. However it is true that a negative
resistance (or differential negative resistance) can be used to excite
a tank circuit and thus make an oscillator. Gunn diode oscillators
work in this manner.<br>
<br>
I also wrote:
<blockquote cite="mid:48EAD2A8.5030903@cyllene.uwa.edu.au" type="cite">...
But now I am starting to think that it might be the load inductor (L2
in the above schematic) and neon on the output that is the real key to
the circuits operation. Maybe the periodic negative-resistance
breakdown of the neon is sucking current through L2, reverse biasing
the collector-base junction (ie forward biasing the C-B diode junction)
and sucking pulses of current from the base tank circuit through this
path!<br>
</blockquote>
But this cannot be an explanation as neon bulb oscillators could never
work at RF frequencies - they seem to be limited to audio frequencies.
Besides the neon in Ron's circuit seems highly overdriven and very
unlikely to be doing anything except dissipating power.<br>
<br>
So I have no ideas as to how this circuit manages to oscillate except
to wave my hands around and suggest stray inductive or capacitive
coupling - which also doesn't seem very convincing.<br>
<br>
Maybe Ron could tell us whether the apparent load inductor and neon is
necessary for operation, or mainly just to indicate when it is
operating correctly?<br>
<br>
Unless Ron ends up giving a description of how a bifurcating oscillator
works, I may have to build one myself just to understand it in more
conventional terms!<br>
<br>
J.
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