FAA pulls funding for LAAS landing systems

"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

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

"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---

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.

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.