Hello Marco,

The J310 is a sturdy device.
In a strong RF field the gate starts to conduct and the gate voltage does not 
rise any higher.
The device protects itself so to speak.

Due to the small size of the 'PCB-antenna' of 30 x 40 mm, voltage build up due 
to nearby 
thunderstorms is low compared to e.g. a 1 meter long whip antenna. Hence 
reports of defunct 
antennas due to lightning are rare.

The most common cause of failure is accidentally sending 100 W RF or more up 
the feed-line! 

73,
Roelof, pa0rdt