From: "Travel Pages" <travelpages@xxxxxxxxx> Sent: Friday, January 14, 2005 6:59 PM > That business of FM ending at the bottom of FAA radiowaves is exactly the > issue still around today concerning the use of cellphones. > > Someone will know better than I, but in the 1960's I believe a TWA DC3 hit > an AA DC4 in fog over the East River in New York --- authorities allegedly > found in a child's carryon a radio in the ON position at the top of the > dial.... and that, I belive, was the beginning of the story about radios > mucking with nav equipment.... > Almost all radio receivers are superheterodynes, invented by Edward Armstrong. who also invented FM radio as it is used today. In a superheterodyne receiver the incoming desired signal is mixed with the output of a local oscillator, which is in effect a little radio transmitter. In many FM receivers, the local oscillator is on a frequency 10.7 MHz above that of the desired station. Thus when tuning in an FM station on a frequency of 101.3 MHz, the a frequency licensed for broadcasting in North America, the local oscillator frequency of such a set is 101.3+10.7=112 MHz, the low end of the aircraft band which covers 112-136MHz. Such a radio tuned to a station at 107.9 will have its oscillator running at 107.9+10.7=118.6, a frequency which might be used for a navaid. Thus the problem at Barksdale is probably not from the radio station per se, but from poorly shielded receivers close to the air base tuned to that station. Good receivers are shielded to prevent the local oscillator radiation from getting out, but many are not. > W Wilson <wlw-jr@xxxxxxx> wrote: > The radio station probably 'just' needs a tuning and a subsequent visit > from a "Flight check" aircraft to fly a series of approaches. > There is probably nothing wrong with the station. I don't know why the investigators are mystified, if my guess is correct. Gerry K8EF (Senior Member, IEEE) http://www.pbase.com/gfoley9999/ http://foley.ultinet.net/~gerry/aerial/aerial.html http://home.columbus.rr.com/gfoley http://www.fortunecity.com/victorian/pollock/263/egypt/egypt.html