Other than GMRS (462/467), what do you need the rest of this band for? I ask because I can't think of what else is in there, besides maybe business radios?
I have a magnet-mount UT-72G antenna that requires a ground plane. It works well on top of my car roof (steel). I have used it with some success on a cookie sheet as well. I'm wondering, would a sheet of aluminum foil function as a ground plane? I'm not serious about doing this, but I wonder if it would be passable?
The first thing that comes to my mind is that you can always dial the power down on a 50-watt radio, but once you hit the max on the 20-watt there is nowhere left to go.
I would think that if there is traffic on the channel, then even though you have filtering codes setup, you would still have some kind of interference such as garbled communications, spotty reception, etc. I am curious what the smarter-than-me folks on here have to say.
I finally mounted the Yaesu FTM-6000R in my car (it's been 30 years since I did an installation!) and I tested the SWR when done. Holy cow, it is awesome. I have it paired with an NMO magnet mount Tram 1181. GMRS (for emergencies) has an SWR of about 1.48. But VHF and UHF were less than 1.1 each! I couldn't be happier.