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Hi Mick,
I didn't know that a spark gap creates FM modulation. But the secondary breakdown through the semiconducting crystal behaves like a spark gap with its negative resistance characteristic. The modulation must depend on the external circuit. The breakdown can be triggered by the base or just by reaching the breakdown voltage of the device.
Regards
Ole
---In [email protected], <mkjekyll@...> wrote :
Ole,
Thanks for the good info.
Do you know if a high speed avalanche transistor creates an FM modulation as does a spark gap?
On 12/28/2018 2:16 PM, onielsen@... mailto:onielsen@... [EVGRAY] wrote:
Hi Mick,
"Can you explain how and if avalanche currents in certain transistors can
mimic multipaction and the electron multiplication of secondary emission?"
The second breakdown https://wiki2.org/en/Second_breakdown#Secondary_breakdown acts like an avalanche that can't be stopped except by disrupting the current from outside the transistor. The first breakdown is kind of like the Zener effect while the secondary breakdown is a negative resistance characteristic where the transistor shorts.
"You mentioned awhile back a concept of power multiplication through
avalanche mode rather than resonance as the system could be much less
finicky. Could you elaborate on this concept?"
The avalanche is like a solid state spark gap and happens very fast like in a few nsec or less.
https://wiki2.org/en/Avalanche_transistor https://wiki2.org/en/Avalanche_transistor
Bipolar transistors optimized to be used in avalanche mode: https://www.diodes.com/products/discrete/bipolar-transistors/special-function-transistors/avalanche-transistors/ https://www.diodes.com/products/discrete/bipolar-transistors/special-function-transistors/avalanche-transistors/
Normal bipolar transistors aren't optimized for avalanche mode operation and their breakdown parameters may vary a lot even having the same type number. They'll still show the breakdown effect.
Understanding Power Transistors Breakdown Parameters: https://www.onsemi.com/pub/Collateral/AN1628-D.PDF https://www.onsemi.com/pub/Collateral/AN1628-D.PDF
"It is interesting to note that during multipaction events much of the
technology present is designed to limit the amplification event to
prevent damage to the devices."
If the device melts or explodes it's no longer useful. This is a good reason for limiting the effect. This means the current must be limited or cut off from the outside as the device can't do it after being triggered.
Regards
Ole
--In [email protected] mailto:[email protected], <mkjekyll@...> mailto:mkjekyll@... wrote :
Ole,
Can you explain how and if avalanche currents in certain transistors can
mimic multipaction and the electron multiplication of secondary emission?
You mentioned awhile back a concept of power multiplication through
avalanche mode rather than resonance as the system could be much less
finicky. Could you elaborate on this concept?
It is interesting to note that during multipaction events much of the
technology present is designed to limit the amplification event to
prevent damage to the devices.
Great data here:
https://en.wikipedia.org/wiki/Multipactor_effect https://en.wikipedia.org/wiki/Multipactor_effect
More intense version:
https://arxiv.org/ftp/arxiv/papers/1112/1112.2176.pdf https://arxiv.org/ftp/arxiv/papers/1112/1112.2176.pdf