I have the Boom Audio hidden antenna. I did not notice any drop in reception.
TIP: I mounted mine against the inner fairing. Zip tied the very ends to the braces. This way I don't have to mess with unplugging it when I remove the outer fairing.
Go to Advance auto parts,auto zone and buy a shorty powered antenna (20.00 bucks) and install it in the fairing length wise up near the windsheild works great for me.....
I have a 2000 flhtpi and just bought an $8.00 mast at auto zone and put it in the fairing, extended it and siliconed the ends where they laid . works great!!
I have the Biketronics one, pretty much sucks. I also noticed that with my retro radio kit there is a antenna cable with a yellow wire, where does that hook up to.