Ed wrote: "the arn-7 is kind of boring as the loop is sealed I think" Hardly boring. And there is an unsealed loop that's compatible with the ARN 7 and SCR 269. It's called an LP 31. The LP 21 is sealed in a streamlined housing. You can see an LP 31 accurately recreated in the transparent nose of Howard Hughes XF 11 as depicted in the movie The Aviator. 73 Mark AF6IM