Reply to post: Re: Concrete Tornado

Hell hath no fury like a radar engineer scorned

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Re: Concrete Tornado

Tubes are tremendously disadvantaged for high frequency use. Their physical size results in high capacitance and inductance.

Normal silicon devices have a far higher output capacitance than a tube, especially at high voltage and high power given the tradeoffs involved to make silicon function semi-reliably at those voltages / powers. For quite a while, tubes were in fact the best technology for very high power, high speed applications -- in fact they still are for some applications, look no further than the humble magnetron. Where semiconductors are made to work despite the inherent problems for high RF work, it's often at a much larger power loss inside the device than would otherwise be tolerated.

Not saying that tubes are de facto better, but it's taken a LONG time to get here. Even now, the silicon devices are more fragile than the old tubes against somewhat common events such as lightning. Where silicon starts to have advantages despite these problems is in resistance to vibration, longer average service life (despite the possibility of EMP / lightning / overstress damage), and of course lighter weight / lower bulk.

Terrestrial transmitters still tend to use tubes. There's a reason for this, somewhat like smaller terrestrial power plants tend to use diesel engines but aircraft do not (power / weight ratio).

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