[AF] NDB antennas, transmitters, etc

[RichardBJohnson@comcast.net]

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Cheers,
Richard B. Johnson
Read about my book
http://www.LymanSchool.org


 -------------- Original message ----------------------
From: "Dave Dunsmoor" <mrfixit at min.midco.net>
>  > The transmitter was made by some company that is no longer in business. I
> forget its name, but Nautel was > instrumental in putting them out of the
> NDB business <grin>!  Ah yes, Wilcox!
> 
> Well, not quite. Wilcox is still in business, is alive and doing well, but
> I'm not certain whether they're producing NDB transmitters or not. Wilcox is
> however, the primary manufacturer of our (FAA) navigation sytems.
> 

I'm not sure I should answer this. You seem to think like some grade-school teacher
that likes to "correct" me, however... Please check out http://www.thalesatm.com/img/section1/navigation/ThalesATM-General-Brochure-Jan2002.pdf

You will learn that the remains of Wilcox was long ago bought by Thales.

>  >It was at the time a 1 kW 4-course radio-beacon array. It transmitted "A"
> in one quadrant and "N" in >another. It occupied a lot of real estate with
> very tall towers very near the airport (scary)! Eventually VOR >navigation
> came about and the 4-course arrays were taken down and replaced with tiny
> bed-springs > supported between two utility poles.
> 
> Again, not quite... VOR did replace the old four course radio range, but the
> VOR antenna system is four
> horizontal loops on the top of the roof of the equipment building, covered
> by a fiberglass "tipi".
>

Yes, again EXACTLY as I stated and the VOR system DOES NOT consist of anything
like you state. The VOR antenna structure consists of a number of vertical unipoles arranged in
a circle, inside a hat-shaped structure,  with an offset antenna at magnetic north located
outside the structure. A VORTAC is a larger structure with more antennas outside, around
the "brim" of the hat.  The individual antennas used to be fed from a spinning capacitor device
called a goniometer with reference to the measuring instrument.
See http://en.wikipedia.org/wiki/Goniometer Now the scanning us performed electronically.

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.
 
> The "bedsprings" antenna is fed by an NDB, the radiating element being the
> vertical wire, and the horizontal wires (the "bedsprings") are the
> capacitive tophat.
> 

So, of course.

>  > The NDBs usually transmit a CW signal on one frequency, and a separate
> carrier, 1020 Hz above it that is > keyed with the identification code.
> 
> I think I've read of this system in Canadian NDB usage (I'm not certain),
> but the US systems all are AM, modulated with a 1020hz ID tone.
> 

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. 

>  >The aircraft receiver "hears" the two signals beating against each other.
> 
> True, if this method were to be used, this would work.
> 
>  > NDB transmitters that can carry
>  > voice are made like conventional AM broadcast transmitters.
> 
> Again, true. And all US NDB transmitters (that I've ever worked on, or read
> about, or heard of)

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.

> all use AM for both ID and voice (if it's configured for voice).
> 

Most NDB transmitters do NOT have voice capability. In fact, I have been flying
since 1971 and the only voice I ever heard on a NDB receiver was from AM radio
stations. See what ICAO has to say about that. http://www.icao.int/anb/panels/acp/wg/f/WGF9/WP/WGF915.doc

>  > Early NDB receivers had a loop antenna that spun around (mechanically),
> plus an additional sense antenna.
>  > At the instant the signal from the spinning antenna changed phase in the
> positive direction, referenced to the > fixed "sense" antenna, the loop was
> lined up with the station. This was displayed in the aircraft as a
>  > needle that always pointed to the station. More modern NDB receivers have
> the same displays, but the
>  > "spinning" is done electronically.
> 
> This end of things, I've never known anything about. Glad to hear about it.
> I have an old WWII ADF loop,
> and have been wondering just what to do with it. I've considered using it as
> a receive antenna for AM station DF work, but have never gotten "a round
> tuit".
> 
> One of these days.....
> 
> Dave Dunsmoor
>