Hi Peter Li,
I think the Zeners will provide some protection against SWR that results in high voltage, not in SWR that causes excessive current.? A bad SWR can cause either, depending on the impedance.? So, yes, 50% of the time, it will help ride through a bad SWR.
I do not equate the TN0110 and Zener combination to be the same.? I have measured spikes over 100 volts on the bench when testing for the Ldi/dt issue that the diode eliminates.? The spike is still there.? The TN devices are just better able to handle it.
At some point, the capability of the Zener to handle the excess energy could be exceeded.? When it does, hopefully, the failure mode is a short (most common for Zener failures) and protects the rest of the QDX.? It is easy enough to replace the Zeners.
Reducing the power to handle SWR mismatch better is a tentative alternative.? There is a minimum power the ATU needs to be able to operate.? A signal above that, yet low enough to prevent damage, is the juggling that needs to be done.? Reduced power for ATU tuning is what all of the commercial rigs do.? They have other protection mechanisms in place as well.
73
Evan
AC9TU
