Rod Madsen wrote:

All very true, but I think the original poster was referring to reception on
the ground (next to the airport or under the plane), not inside a cockpit.

Several years ago, I went to a ham radio shop and had them cut an roof mount
antenna for my ICOM 21. I believe I had them cut it for 128 MHz and 3/4 wave
length. I got awesome performance from my car. I could hear the ATIS and talk
with ground control five miles from the airport on the freeway. I could drive
along I-5 on the coast and talk with LA Center's RCO on Catalina Island.