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#21
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"JJ" wrote in message ... The LAAS correction uplink is in the 150MHZ area. It would have been more susceptible to FM interference than a Localizer. Just another little tidbit of info. Wrong. The LAAS VHF Data Broadcast (VDB) is capable of existing on 108.00 MHz to 117.75 MHz (LOC and VOR freqs). The plan is to use VOR freqs (114.00 and up) until ILS freqs become available thru decommissioning (if it ever goes that far.) Since the VDB is a D8PSK digital signal it is not significantly affected by the interference from the FM band. Bob Noel wrote: In article , Javier Henderson wrote: except in for the problems with ILS in Europe... What's the problem with ILS approaches in Europe? Frequency congestion? yes. and interference from FM radio stations. And multipath. Terrain and new high-rise construction around airports creates multipath that puts "bends" and "noise" in the ILS path (it's an AM system). Too much of either and you can't use it for CAT III. MLS mitigates all three of those problems. There are 200 channels vs. 20 for ILS. It operates in the 5.1 GHz band so there's no high power transmitters operating near it avoiding the FM broadcast interference. And the use of a scanning beam instead of an AM differential signal greatly improves multipath rejection. Heathrow put in two new MLS ground stations and there are others scheduled to be installed on the continent. Gerry |
#22
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Stan Gosnell wrote:
Very possibly. Harmonics can do as much damage as the fundamental frequency. Harmonics, from FM broadcast radio? The FM broadcast band is 88-108MHz. The second harmonic of the lowest of those frequencies is 176MHz (the highest second harmonic is 216MHz), well above 150 MHz. The third harmonic is higher, the fourth higher yet, etc. At 108MHz, the most likely sources of interference from FM broadcast radio are spurious signals (lousy filtering at the transmitter), or front-end overload (very strong signals overloading the ability of the receiver to reject nearby frequencies). I'd be inclined to think the latter, given the transmission purity standards. --Dave -- Dave Buckles http://www.flight-instruction.com |
#23
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"Dave Buckles" wrote in message = news:vpw0c.5983$fD2.3759@lakeread02... Stan Gosnell wrote: Very possibly. Harmonics can do as much damage as the fundamental=20 frequency. =20 Harmonics, from FM broadcast radio? The FM broadcast band is = 88-108MHz.=20 The second harmonic of the lowest of those frequencies is 176MHz = (the=20 highest second harmonic is 216MHz), well above 150 MHz. The third=20 harmonic is higher, the fourth higher yet, etc. At 108MHz, the most=20 likely sources of interference from FM broadcast radio are spurious=20 signals (lousy filtering at the transmitter), or front-end overload=20 (very strong signals overloading the ability of the receiver to reject = nearby frequencies). I'd be inclined to think the latter, given the=20 transmission purity standards. =20 --Dave =20 Exactly, Dave. But if someone in the airplane is playing an FM broadcast receiver, it's local oscillator will likely be 10.7 MHz above the tuned frequency, i.e. 98.8, 99.0, 99.2, etc., up to 118.6 MHz. That's unrelated to FM stations interfering with a data channel, though. ---JRC--- |
#24
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Dave Buckles writes:
Stan Gosnell wrote: Very possibly. Harmonics can do as much damage as the fundamental frequency. Harmonics, from FM broadcast radio? The FM broadcast band is 88-108MHz. The second harmonic of the lowest of those frequencies is 176MHz (the highest second harmonic is 216MHz), well above 150 MHz. The third harmonic is higher, the fourth higher yet, etc. At 108MHz, the most likely sources of interference from FM broadcast radio are spurious signals (lousy filtering at the transmitter), or front-end overload (very strong signals overloading the ability of the receiver to reject nearby frequencies). I'd be inclined to think the latter, given the transmission purity standards. "Harmonics" from FM broadcast is a little more complicated than you describe. The transmitted signal is spread over the center frequency +/- the modulation frequency. The "purity" of the transmitted signal isn't that pure even when in compliance with FCC requirements. At close range, all sorts of signals can be detected. However, as several people noted, a signal with digitially- encode information /probably/ isn't going to be bothered much. But "probably" doesn't necessarily get you reliable operation. |
#25
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Not quite. I had lunch with one of the FAA guys, and he told me there were
some significant technical hurdles that were not adequately addressed. They were much further from fielding than anyone was led to believe. I also heard that WAAS will never get close to Cat I cert... Then again, he stated that legacy systems can't even meet the new performance specs to begin with. Looks like the bar was set too high... wrote in message ... JJ wrote: LAAS (Local Area Augmentation System) was to provide CAT 2 and 3 ILS capability at major airports by fine tuning GPS and up loading correction signals to aircraft. FAA has canceled the program. Looks like the ground based ILS systems once slated for removal by 2010 are here to stay. They finally figured out the airlines are married to ILS, both domestically and internationally. |
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