[TowerTalk] SWR Problem Balun or lightning protection?

[Tony]

All,

The SWR on my 5 element mono band Yagi rises after I key down for a few 
minutes. The 2:1 SWR bandwidth behaves normally until the problem 
occurs. The SWR goes to normal after waiting a few minutes, but then the 
problem starts again after I key down for a while.

The only things inline are the lightning protection (polyphaser) and the 
balun which is mounted at the antenna. The antenna is made by M2 and it 
uses an M2 balun.

I'm going to bypass the lightning protection tomorrow as a process of 
elimination, but I was wondering if the problem is more likely to be 
caused by the balun?

Thanks,

Tony