JJ,
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I agree with Gordon's suggestions.? IRF520 would be a more robust part, and the TVS protection is a good idea as the driver circuit can deliver higher than the gate voltage if driven to full power.
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Also, Joel suggests that the pin diode current should be increased by 470 to 330 ohm replacements.? The bias increase is another good idea.
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Another suggestion is to add the resistors to the drain of Q101 and series with D20 and D21.? Gordon posted this here:
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You should verify the signal purity before putting it in the air.
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73
Evan
AC9TU
