> I suspect the problem might be the lack of a copper or brass shield
between
> the toroid and the conductor carrying the RF.
Directional couplers always require care to make flat, but the problem is
almost never a "shield" between the current transformer secondary and
primary.
The largest problems are almost always improper layout, connections, or lead
dress that cause ground loops around the sensing diodes.
As I recall the couplers in those amps are reasonably flat when everything
is built correctly. You calibrate around 7 or 14MHz, never at one end. In
particular you have to watch PC board grounding to the RF connector and the
shield grounding of the lead from the RF deck up to the grounding point near
the directional coupler. Be sure you did the hardware stack correctly in the
transformer, and the especially includes using a Teflon center insulator and
a insulated washer to hold the board up.
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