JoseLopez99
Topic Author
Posts: 1
Joined: Wed Jan 08, 2020 4:39 pm

Instrumental Landing system

Wed Jan 08, 2020 4:43 pm

Hello everyone,

I’m doing a report about the Instrumental Landing System, and I have a question.

The Instrumental Landing System is a worldwide used system to assist airplanes to land. It’s operation principle it’s explained here:

https://landingsystem.com/

My questions are, could someone tell me if is there any difference if the localizer signal is sent in log-periodic type or dipole antennas?

And, In the localizer, a signal can be sent to confirm whether or not the information is properly received(NAV signal) . Does somebody know how is this clearance signal sent?

Thanks a lot!
 
Yikes!
Posts: 348
Joined: Sat Oct 13, 2001 4:51 pm

Re: Instrumental Landing system

Sat Jan 11, 2020 5:36 am

Best I can find to answer your query:
https://en.wikipedia.org/wiki/Instrument_landing_system
 
timh4000
Posts: 320
Joined: Fri Dec 07, 2018 1:14 pm

Re: Instrumental Landing system

Thu Jan 16, 2020 5:22 am

Sometimes when I find something so hard to deal with and explain, I try to work around it.Only IF it can be done in a way that gives the reader the info they need.
 
User avatar
rjsampson
Posts: 396
Joined: Sat Jul 31, 2010 12:00 am

Re: Instrumental Landing system

Thu Jan 16, 2020 6:07 pm

I know this has been answered before, but I cannot find it on the forum, or the internet for that matter... the GS antenna has essentially 2 physical transmitters on the different frequencies to create the slope. I'm STILL not clear on while the localizer antenna has a 12-18 transmitter array by comparison. Could someone please explain?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
User avatar
Florianopolis
Posts: 325
Joined: Sun Mar 29, 2015 2:54 pm

Re: Instrumental Landing system

Fri Jan 17, 2020 12:30 am

rjsampson wrote:
I know this has been answered before, but I cannot find it on the forum, or the internet for that matter... the GS antenna has essentially 2 physical transmitters on the different frequencies to create the slope. I'm STILL not clear on while the localizer antenna has a 12-18 transmitter array by comparison. Could someone please explain?


I've always been curious why they were so different, and this is all I could come up with...

- You could take a localizer antenna array, put it up vertically, lean it back 3 degrees, and put it next to the runway's TD zone. But then you've got a 100 foot tall obstruction right next to the runway. And the earth being on one end of it would make for some nasty reflections. (Imagine what a big reflecting plate installed on one end of a localizer antenna array would do to L-R guidance. Or even a vehicle near it.)
- The glideslope signal extends all the way into the ground. The signal appears to come out of the ground because the antenna is bouncing half the signal off the ground in front of the GS antenna*, so the airplane "sees" the glideslope signal all the way to touchdown. If you used the localizer setup idea described, the glideslope would stop 50 feet from the ground.

TLDR: they're both built to provide good signals without being too tall, or the earth causing reflection problems.

* This describes your standard "image type" GS antenna. An "end-fire" GS antenna don't bounce a signal, which is important where the terrain in front of the GS antenna isn't level and smooth (the "fresnel zones").
 
N47
Posts: 61
Joined: Tue Sep 26, 2017 7:38 pm

Re: Instrumental Landing system

Fri Jan 17, 2020 4:18 am

Here is a really good link i often refer to, its fairly technical but it does a great job at explaining the wizardry behind ILS. It also has a good bit about clearance signal in there as well:

https://youtu.be/8g6ZMdjnIDw

As for the # of elements in LOCs. In the US the standards 8, 14, 14/10, and 20/10 (the /10 signifies that the clearance signal is radiated from the inner 10 elements). 8 elements have wider beam more prone to multipath from hangars terminals etc. which degrades peformance. The higher the natrower the beam the more resilient to multipath and the better performance. IIRC CAT II/III have to at least be 14/10 or 20/10. Again this is US, in europe and elsewhere they may have different set ups.

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