Ken wrote: > AM aircraft radio has been around since the end of spark and > steadily growing world-wide since that time. It was solidly in > place -long- before FM was a gleam in Armstrong's eye.
Er...I'm not sure how that supports an argument that transition to FM was *at any point and time* considered *by any responsible party* to have characteristics that were more desirable than AM for aircraft communications. The characterization that AM was "solidly in place -long- before FM was a gleam in Armstrong's eye" refers accurately only to the era when aircraft communications were only on medium and high frequencies... an era when long-range aircraft communications often still made use of Morse CW (hence the FCC Element 7 exam for Aircraft Radiotelegraph Endorsement, now discontinued). The transition from MF/HF to VHF for aircraft communications received its greatest push with the UK's pioneering use after 1940 of aircraft AM command sets operating in the range of 100 to 156 MHz. This sparked the allied US military's transition from MF/HF command sets to VHF command sets, one of the earliest being the Western Electric 233A set. At this point, VHF FM could have been *very easily* adopted, had it not been for its undesirable capture effect. Aircraft VHF-AM was chosen long after FM had been developed. The decision to use AM was purposely made. The adoption of aircraft VHF-AM was NOT the result of constraints from earlier legacy technology. All civil aviation eventually adopted the military standard of VHF-AM, although up to the mid-1950s many private aircraft continued to use MF/HF sets with receivers in the 200 to 400 kHz range and a transmitter on 3105 (later 3023.5) kHz...still far from a universal commitment to VHF-AM at that late date, had VHF-FM been a better choice. Further, by 1945, the US military began exploring UHF for aircraft comms. These new sets had no reason to stick with AM, if FM were superior. But FM was not superior...or as good. AM was chosen for use in the military UHF aircraft band as well. > It remains that the staggering cost of conversion to FM is the > real reason it continues today. That is a gratuitous assertion for which my decades of study in this area finds no substantiation. 73, Mike / KK5F ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
