Farhan, Gordon;
I have back-to-back Zeners from the final FET Gates to Ground on my DE. (No series resistors) Before installing them I tested how well they would clamp at RF frequencies, due to concerns I had about their speed. My tests using a scope and RF at 30 MHz showed that the 5 Watt Zeners I selected did in fact clamp at their design voltage.
The idea is one recommended by W1FB and at least one MACOM spec sheet (MRF275G). I have also come across sources that claim this is a bad idea.
At the time, we were all looking for the cause of final FET failures in the DE. We found low frequency spurious oscillations in the V1, caused by feedback paths in the TR switching circuit, TR Timing problems, excessive drive capability, and excessive low frequency gain. Those issues have since been addressed, reducing if not eliminating the potential for an over-voltage situation at the gates of the final FETs.
I've left the Zeners installed in my DE. As we make progress towards reducing harmonics, spurs, IMD, etc, they may end up getting removed.
73; Steve, N3SB
