Power on or power off, the front end will still see the RF power and you will do the damage.
Not having been the owner of a scanner in my some 40 years playing with servicing radios, my
first thought would be to go back and tell GRE and the other scanner mfg to spend the 50 cents
and add the protection. They only look at the bottom line to make the max profit from each sale.
To my electronics and radio brain, they have designed an inferior product that doesn't stand up
to the normal use in a high RF environment. They are the ones that need to make the change.
If their management is smart, they would offer to make this mod for no charge to those that request
it. I guess you could wait until the warranty has expired and just go do it yourself.
Jim
Would I be correct in presuming if the scanner is powered off while the radio is transmitting, you don't have a worry with blowing out your scanner?
I've thinking about a homebrew deal that powers down the scanner whenever I remove the radio microphone. Usually I remember to manually turn the scanner off before transmitting, but I'm human and miss sometimes.