[AF] NDB antennas, transmitters, etc

[Dave Dunsmoor]

 > 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.

 >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".

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.

 > 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.

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

 > 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