must be confusion. here's a except from the link:

Reader Tip: For frequencies in the normal FM band (90-100Mhz) a length between 26 and 31 " will be fine. If you want to go smaller I recommend you use multiple of this ie 13 to 15.5" in order to maintain reasonable reception. - John the Ham radio operator and SVT driver (not at the same time :-)

so it would seem that 26"- 31" is acceptable, yet should you want to go shorter, use a mutiple of those numbers to maintain signal strength.

 

I see... so 26-31" is ideal, but if you're going to go taller you should double it and if you're going to go shorter you should cut it in half.

 

I chopped my antenna so it's around an inch higher than the roof. Did it affect my reception? I have no idea, I never listen to commercial driven AM/FM.

 

Nice fit just don't run over something as you enter the garge or you'll hit your roof.

 

I blindly cut mine down... dunno how long it is really... probably about 18" long.. gets the city stations just fine.

 

I have cut antennas in the past and have never had problems picking up radio stations. As long as you don't make it less than 10" tall, it should be ok. Like I said, make it about 1" taller than your cab and it will be fine. FM radio stations do not use the same frequencies as short wave radios.

 

i was backing out of my garage about a year or so ago when the little ball on the end of my antenna wedged into the perfect spot of the bottom of my garage door...darn near pulled the whole garage door out before the ball popped loose

i cut down my antenna to just above my cab, but didn't replace the ball for that reason