Path: utzoo!telecom-request Date: Sat, 18 May 91 19:43:35 CST From: Jack Winslade Newsgroups: comp.dcom.telecom Subject: Re: Cellular Phone Use in Aircraft Reply-To: ivgate!jsw@uunet.uu.net Message-ID: Organization: TELECOM Digest Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 369, Message 1 of 10 Lines: 58 In a message of <16 May 91 20:45:26>, Ted Marshall writes: >> the navigation equipment. Most airliners now use longer range >> navigation systems like LORAN or various satellite-based systems, >> which can't be upset by FM interference. [...] > This is just plain wrong! Loran-C and GPS (satellite) navigation are > being used in air navigation, but, to my knowledge, mostly in smaller > aircraft. GPS, in particular, cannot be used 24-hours/day because > there are not yet enough satellites in place. Over-ocean operations do > use other forms of navigation, including inertial navigation, but > almost all domestic US enroute navigation is via VOR (VHF > Omnidirectional Range). Also, bad weather approaches into all major > and many minor airports are via ILS (Instrument Landing System). When I was in the Coast Guard I spent more time working with Loran equipment than I care to admit. ;-) Loran-C (the type of Loran that is used today) uses a portion of the frequency spectrum that is SO far from that which cellular phones use that unless the loran receiver is defective, it will be essentially blind to interference from any cellular transmissions on board. Loran-C uses pulse trains of 100 kHz RF. Yes, I said that right. 100 kilohertz -- that's well below the AM broadcast band and almost four orders of magnitude removed from the cellular frequencies. (Loran = 10 ** 5 Hz and cellular is ABOUT 10 ** 9 Hz.) HF transmitters in the kilowatt range are routinely used on ships that navigate with Loran-C, with the HF and loran antennas being quite close to each other. Very seldom will interference (to the loran from the radio transmission) occur in this case, let alone the case of a one to three watt UHF transmitter as in a cellular phone. Now (no grin here) for those of you who happen to live very close to a Loran-C transmitting station, this case of no interference does not hold true the other way around. These transmitters pump out RF pulses in the megawatt range and they have been known to bleed into telephone lines (sounds like an old mechanical teletype running in the background) make one heck of a racket in AM and (sometimes) FM radios, and even cause black and white horizontal 'strobe light' bars on television pictures. Good Day! JSW (Charlie-Golf 1967 - 71) [Moderator's Note: Have you ever traveled through the rural area in northern Wisconsin where the ELF (extremely low frequency) transmitters are located? They send/receive radio transmissions to submarines. The antennas are strung up and down the highway on telephone poles! The frequencies which can travel through the earth and under water are sort of special; they make it possible for a submarine to receive radio signals without having to expose at least a little of itself above water; an important feature when used in a spy operation for military intelligence ... but the base station antenna has to be about a mile in length! PAT]