VP-TAA
I don't particularly care what the FAA thinks about my 'home made' headset matching device - I fly aircraft built, registered and certified in the UK! There is life outside of the USA you know..
AND, if you look at the commercially available items for sale in the UK, for which you are charged in excess of £100, they are probably made by a 16 year old school leaver with hardware bought at the local Maplin store - hardly cutting edge technology is it?
Chill out
