On Thu, 30 Nov 2000 09:48:59 -0700 Dave D'Epagnier <DAVED@ctilidar.com>
writes:
>
> Thanks Marv, so do the articles and Orr Handbooks have detailed
>expalnations of how they work or do they just show a schematic and parts
>list? Thanks for the QST references. I'll see if I can find them.
>
> --Dave
>
Hi Dave,
I'm afraid they typically don't explain the concept; just parts
lists... and sometimes they neglect a curious bit of info like the core
material!
They function because the forward components (voltage and current) of
the signal in a transmission line are in phase and the reflected
components are 180 degrees out of phase.
A sample of the line voltage is balanced with a sample of the current,
then the two signals are added, which cancels the reflected component, to
measure "power" in the forward direction. Note that it is really the
line voltage, not power that is being sensed -- calibrate your meter
scale accordingly! And since this is a voltage based measurement, it
will only be correct at the selected line impedance.
The reflected "power" is measured similarly by using an opposite phase
sample of the current in the addition.
As far as design techniques, the voltage samplers are simple
capacitive dividers and the current sampler is a current transformer. It
should be easy enough to derive the "lost" equations.
There are undoubtedly some secondary effects, with regard to stray C &
L, that need to be considered for the unit to retain accuracy over a wide
frequency range, such as the 2-30 MHz band.
73,
Marv WC6W
*
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