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Current through coils
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March 14th 06, 11:36 PM posted to rec.radio.amateur.antenna
Owen Duffy
Posts: n/a
Current through coils
On Tue, 14 Mar 2006 17:03:49 -0600,
(Richard
Harrison) wrote:
Tom, W8JI wrote:
"A traditional directional coupler works by comparing voltage across the
line at any one point to current in the line at that same point."
Almost. It compares a voltage sample to a current sample, both of which
have been converted into d-c voltages. These have been carefully crafted
to be exactly equal d-c voltages regardless of the power level in the
line.
When you convert a sample of the RF voltage at a point to DC voltage
you have a DC voltage proportional to the magnitude of the RF voltage
at the point.
When you convert a sample of the RF current at the same point to DC
voltage you have a DC voltage proportional to the magnitude of the RF
current at the point.
You cannot use these two samples to determine generally the magnitude
of the reflection coefficient (and hence VSWR), much less independent
samples of the travelling waves.
No, neither a directional coupler nor a common reflectoter work as you
describe Richard.
Owen
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