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Re: Random TC Questions- streamer current

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

At 12:32 PM 3/19/2005, you wrote:
> Almost certainly, because the Q of the filament is so low that the
> reactance probably doesn't count below 1 MHz or so.  There are tubes
> specifically made for power measurement which consist of two identical
> straight filaments mounted in an evacuated envelope.  The power to be
> measured is fed to one filament and the current in the other adjusted
> from a separate source to give equal brightness (the eye is very
> sensitive to small brightness differences), at which point the two
> powers can be considered equal.  I've used a similar method to measure
> powers at frequencies as high as 1200 MHz and the accuracy, compared to
> a VHF wattmeter, seemed to be within 10% or better.

And the inaccuracies are probably evenly divided between the lightbulb and
the wattmeter, or due to things like mismatch.

The VHF wattmeter probably uses two resistors and thermal probes to operate off pretty much exactly the same principle too ;-))