A good discussion on testing using a return loss bridge should be
found wherever the old Hewlett Packard App. Notes are on the web.
A return loss bridge in its simplest application is a dual
directional coupler with detectors (or power meters) on the coupled
ports. The forward port samples the forward power on the line and the
reflected port the reflected power coming back from the load being
looked at. If you have power meters on both ports, the difference in
these power levels is the return loss of the device under test. You
can relate return loss to VSWR, of course. If detectors are on the
ports, the detector on the reflected port will have almost equal
voltage as the forward detector (for a terrible VSWR) and
progressively less voltage as the load VSWR gets better (toward 50
ohms).
Roger
W5RD
>
> Couldn't one use a directional coupler instead of a RL bridge? The
> directivity probably wouldn't be quite as good, but a surplus
coupler would
> be a lot cheaper.
>
> Bob NO6B
>
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