[AF] NDB antennas, now VOR, DF, etc.

[Dave Dunsmoor]

> I'm not sure I should answer this. You seem to think like some
grade-school teacher
> that likes to "correct" me,

As it happens, I work on these systems and have been doing so for about 28
years, so I feel that I know about this stuff to the degree that I can with
accuracy and authority, make the statements that I have.

>however... Please check out
http://www.thalesatm.com/img/section1/navigation/..........
> You will learn that the remains of Wilcox was long ago bought by Thales.

Yeah, I know, Wilcox was bought out, but that's a recent development, and
you are correct.

> Yes, again EXACTLY as I stated and the VOR system DOES NOT consist of
anything
> like you state.

Well, here you are mistaken. I've been maintaining and certifying them for
many years now. But, if you've never worked on one, or ever seen one, this
might be an easy mistake to make.

>The VOR antenna structure consists of a number of vertical unipoles
arranged in
> a circle, inside a hat-shaped structure,

No, the 16 antennas that you think are vertical unipoles are actually
horizontal dipoles (enclosed inside a fiberglass shield), and are the
system's receiving monitoring antennas.

> with an offset antenna at magnetic north located
> outside the structure.

This "offset antenna" is not part of the VOR, but part of the TACAN (again,
monitoring), and is typically located at 315 degrees, not 360 (north).

>A VORTAC is a larger structure with more antennas outside, around
> the "brim" of the hat.

Ah, I think you're referring to a Doppler VOR. They do have about a jillion
radiating antennas around the perimeter of the counterpoise. They are not
common, only placed in service where the regular VOR won't work due to
reflections, etc.The term VORTAC however refers to a VOR co-located with a
TACAN.

>The individual antennas used to be fed from a spinning capacitor device
> called a goniometer

Yes, the goniometer was one of the part of the system, the rest of it
resembled a standard AM transmitter, as are the current versions. The AM
transmitter and the goni each fed the four Alford loops in such a way that
the AM was radiated equally from all 4, and the goni radiates two sideband
only signals phased at 90 degrees to each other to opposing pairs of
antennas. The end result is a signal that contains both AM and FM, the phase
relationship of one to the other describes the azimuth the where the
receiver is located.

The current versions use a goni also, but like all the other signals that
comprise the system, it's done electronically, as you stated.

> The crossed loops that you might have seen are for a receiver
direction-finder antenna.
> It used to be possible for a "lost" pilot to call FSS and request a "DF
steer." That's what
> was used.

No, the old DF system (and the "new" DF as well) used 16 vertical dipoles
mounted on a mast about 12' high out in the middle of the field. Yes, I've
worked on both of those systems, too.And both have been mostly
decommissioned.

Now if there was a "crossed loop" antenna DF, that was before my time, and
all the old timers that might have been around to see it are now long
retired. I started on a version that used nuvistor tubes, and those were old
when I started.

> No. the word ALL is wrong. In fact MOST low power NDBs, the ones used as
> "compass locators," co-located with the 75 MHz outer-marker transmitters
> are offset carrier devices.

Well, I've never seen or heard of one like that. None in our inventory that
I'm aware of. Nautel doesn't make any like that, neither does Scientific
Radio. However, it could be, but again, I work on them, and have been doing
so for quite a few years, and have never seen one.

> Of course it's true. Do you think I make these things up? You are not,
> repeat, NOT, my grade-school teacher who should continually "correct" me.

No, I'm just the guy who works on all these systems. I know how they are
built, and how they work.

> Most NDB transmitters do NOT have voice capability.

I too have never heard voice on an NDB, however, they all have the voice
input terminals, so, technically, have the capability. Just not used.

Dave