rjsampson
Topic Author
Posts: 216
Joined: Sat Jul 31, 2010 12:00 am

### Localizer And VOR Antenna Question

Hello,

In flight school, the mechanics of a glideslope antenna was well explained (what with two antennae on the glideslope mast sending two signals that are translated by the horizontal crosshair or chevron as to where you are on the path, etc.)

However, the mechanics of a localizer (and for that matter a VOR) station were never discussed.

Why does a localizer station have multiple antennae and, for that matter, why does a VOR have several (or much more than several) transmitting antennae? How do these stations work?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days!

tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

### RE: Localizer And VOR Antenna Question

 Quoting RJSampson (Thread starter): However, the mechanics of a localizer (and for that matter a VOR) station were never discussed.

As far as I know, the localizer works just like the glideslope, it's just rotated 90 degrees.

 Quoting RJSampson (Thread starter):Why does a localizer station have multiple antennae and, for that matter, why does a VOR have several (or much more than several) transmitting antennae? How do these stations work?

I can't speak to why localizer antennae are built the way they are, but the VOR is transmitting to signals...a main signal (the big central antenna) and an electronically rotating signal (all the little ones). The phase difference between the two defines the radials of the VOR.

Tom.

zeke
Posts: 11445
Joined: Thu Dec 14, 2006 1:42 pm

### RE: Localizer And VOR Antenna Question

 Quoting RJSampson (Thread starter):However, the mechanics of a localizer (and for that matter a VOR) station were never discussed.

These documents is more than you will ever need to know operationally as a pilot, they describe how the various systems work.

 Quoting RJSampson (Thread starter):Why does a localizer station have multiple antennae and, for that matter, why does a VOR have several (or much more than several) transmitting antennae?

Essentially it has to do with antenna design, with better mathematical models of how antenna radiate their signals, more advanced antenna designs are used to provide a more uniform and accurate radiated signal and that is less susceptible to the normal inherent errors in those systems, and the physical surroundings.

The more modern the installation, generally the more antennas you will see installed for a given function.

 Quoting tdscanuck (Reply 1):VOR is transmitting to signals...a main signal (the big central antenna) and an electronically rotating signal (all the little ones).

If you see around 48 little antennas arranged in a circle of 44' diameter, that would be a doppler VOR station which uses a doppler shift between the AM reference signal to the FM variable signal to generate the phase difference. The rotating signal generating the phase difference is used in the older conventional VORs.

If you have a cone or mast mounted in the middle of the VOR/DVOR station, that is normally a sign of a collocated DME.
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mmedford
Posts: 449
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### RE: Localizer And VOR Antenna Question

First off; we like to call ourselves Technicians/Engineering Technicians...not mechanics...

tds is right, the pure concept of space modulation is the same in free space to the aircraft. On the ground we use different antenna arrangements to build arrays that help us achieve the radiated signal we are looking for; in terms of path/course and clearances. To give the aircraft a true centerline as possible with regards to surrounding objects that can affect the radiated signal in space (eg; hangar, buildings, etc..)

There are 2 types of VOR as zeke has covered; a conventional and a doppler; Again to the aircraft it's the same deal, but to us on the ground it helps achieve a better signal with regards to accuracy, integrity and advertised service area.

But to correct Zeke; the cone or mast; is either the VOR antenna (Conventional VOR) or Monitor Antenna (Doppler VOR)...the DME uses a normal halfwave dipole.

*goes back into equipment shed*
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zeke
Posts: 11445
Joined: Thu Dec 14, 2006 1:42 pm

### RE: Localizer And VOR Antenna Question

 Quoting mmedford (Reply 3): But to correct Zeke; the cone or mast; is either the VOR antenna (Conventional VOR) or Monitor Antenna (Doppler VOR)...the DME uses a normal halfwave dipole.

The white mast in the middle is what I was referring to, I always thought they were the DME antenna.

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sfotom
Posts: 26
Joined: Fri Sep 04, 2009 9:50 pm

### RE: Localizer And VOR Antenna Question

 Quoting mmedford (Reply 3):First off; we like to call ourselves Technicians/Engineering Technicians...not mechanics...

Uh, I think he was using the term "mechanics" as understanding the way the system worked, not as a term used for those who work on that system.

Tom

Elevated
Posts: 125
Joined: Sun Feb 14, 2010 6:52 am

### RE: Localizer And VOR Antenna Question

 Quoting mmedford (Reply 3):First off; we like to call ourselves Technicians/Engineering Technicians...not mechanics...

My, oh my.

Fly2HMO
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

### RE: Localizer And VOR Antenna Question

 Quoting Zeke (Reply 4):The white mast in the middle is what I was referring to, I always thought they were the DME antenna.

It is AFAIK, but I believe the monitoring antenna is immediately under it (the white dome). Not all DVORs seem to put the DME antenna in the middle.

Here's a DVOR with the DME antenna on the left side:

You can kinda see the monitoring antenna in the middle.

Not sure what the dipole to the right is, but probably some sort of monitoring antenna as well.

[Edited 2010-09-16 10:50:57]

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

### RE: Localizer And VOR Antenna Question

The conical center antenna shown is part of the VOR itself. The rod resembling a largish cell phone antenna would be your DME.

http://www.scribd.com/doc/36326940/Vor
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Fly2HMO
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

### RE: Localizer And VOR Antenna Question

 Quoting FredT (Reply 8):The conical center antenna shown is part of the VOR itself.

Show and tell time!

A plain VOR (no DME, TACAN or any other fancy stuff):

I don't think there's any left like that around in the US anymore.

Most of all the off-airport VORs I've seen in the US look exactly like this:

The cylinder at the very top is the TACAN.

A doppler VOR would be like what my last post, or Zeke's shows, but here's a DVORTAC for good measure:

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