Plasma wire -- turning an antenna on and off very quickly

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Discussion Overview

The discussion revolves around the concept of using plasma in a wire to control an antenna's conductivity rapidly. It explores the feasibility of employing a fluorescent light bulb as an element in the antenna, particularly in the context of switching the antenna on and off quickly.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that using a fluorescent light bulb in an antenna could allow for rapid switching between conductive and non-conductive states when high voltage is applied or removed.
  • Others argue that this concept is analogous to the behavior of lightning, where plasma channels conduct electricity during discharge.
  • A participant notes that early radar systems utilized gas discharge tubes for similar purposes, allowing for switching at frequencies around 10 kHz.
  • Concerns are raised regarding the limitations of this approach, including the operational frequency constraints of the tube, potential RF power issues, and the introduction of high noise levels when receiving signals.

Areas of Agreement / Disagreement

Participants express differing views on the practicality and effectiveness of using plasma in antennas, with some supporting the idea and others highlighting significant limitations. No consensus is reached on the viability of the proposed method.

Contextual Notes

Limitations include the operational frequency of the fluorescent tube, the RF power levels required for effective operation, and the noise characteristics associated with using such tubes in receiving applications.

arydberg
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Someone asked if it was possible to conduct electricity through a wire with a plasma. I ran across a article about a inventor who wanted to turn a antenna on and off very quickly. He said it was possible to do this by using a florescent light bulb as a element in the antenna. When a high voltage was applied to the tube it became conductive but when the high voltage was turned off it became non conductive.
 
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Sounds accurate, that's what happens with lightning in the atmosphere, when the trails are forming they cause plasma channels which conduct the main discharge.
arydberg said:
I ran across a article about a inventor who wanted to turn a antenna on and off very quickly.
If you want more information you would have to supply a link or a specific reference...
 
The transmit/receive switches in early radar sets were based on small gas discharge tubes that conducted during transmit. The impedance mismatch created by the gas discharge in the line to the receiver reflected energy and so protected the sensitive receiver mixer diodes from the transmit energy. Those TR switches could switch on and off at 10kHz.
https://en.wikipedia.org/wiki/Duplexer#Transmit-receive_switch
 
arydberg said:
Someone asked if it was possible to conduct electricity through a wire with a plasma. I ran across a article about a inventor who wanted to turn a antenna on and off very quickly. He said it was possible to do this by using a florescent light bulb as a element in the antenna. When a high voltage was applied to the tube it became conductive but when the high voltage was turned off it became non conductive.
This idea has a number of limitations.
1) The tube can only operate at a few kHz, whereas transmitters can often be pulsed much faster than this - so why do it?
2) The RF power itself would fire the tube at power levels above a few tens of watts.
3) If used for receiving, the tube will introduce a very high noise level. In fact these tubes are used as noise sources.
 

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