How exactly does an NDB work?

[Andy Neill]

sexton- you mean SEXTANT?

Since a sexton is a church officer or employee who takes care of the church property and performs related minor duties (as ringing the bell for services and digging graves), I think he meant sexton.

It's like flying a 777 with a sexton.

"Uh, Brother Fisher, I need to check my position as we're going into Gatwick. Would you mind getting an updated fix?"

 

[cl-65link]

http://www.cogtech.com/EXPLORER/sextant.htm

 

[RedheadCFI]

NDB's should be a thing of the past because they DON'T work half of the time. The only thing they're good for is outer markers. Its always been my understanding that they work off the PFM theory. (Thats Pure Fu*king Magic for anyone un-familiar)

 

[80/20]

ktulu34535 are you asking how the NDB ground station works?
Transmitter, oscillator, carrier wave, modulation, ident, antenna mast shapes and so on?

 

[ktulu34535]

would be great

Well the avweb article explained what I was wondering about as far as the loop and sense antennas and what kind of waves are produced and how the ADF interprets them.

But if you are willing to explain how the ground transmitter works I would love to add that to my notes.

Thanks

 

[80/20]

NDB GROUND STATIONS

The NDB transmitter is a very basic transmitter with a simple radio frequency oscillator that produces a carrier wave. The oscillator "filters" out all undesirable frequencies and will only allow one selected frequency to pass through. It produces a carrier wave, which consists of two electromagnetic fields: an electric field called the E-field and a magnetic field called the H-field. The H field, I believe, is named after the American physicist Joseph Henry who discovered the induction of electromagnetic fields.

See the VNugget's recommended link about how the ADF loop antenna works

Modern NDBs use an audio morse code for identification. Audio can not be transmitted directly through space and it is modulated onto the carrier wave in a modulator. After being modulated the signal is sent to an amplifier where it is boosted to the final transmission power. The power of an NDB is based on its intended use. It may vary from 15 watts to several kilowatts. The signal continues to the antenna, which radiates the electromagnetic energy in all directions. NDB antennas may be a single mast or wires strung between masts.

NDBs have an automatic shutdown feature if tone, modulation, power or other essential functions deviate beyond a set level. Modern stations have dual transmitters where a shutdown signal initiates a transfer from the primary transmitter to the secondary transmitter.

Teach all this when introducing ADF?
Too much information can be just as bad as too little. It is difficult to learn NDB tracking. I would keep it short and simple, focus on the practical flying and basics. Use some simple rules about how to track a bearing to and from the station. When the student is ready for more I would focus on the many limitations and factors that can make NDBs inaccurate. I would save this "nice to know story" about NDB stations for the student that wants to know more or for a more advanced program.

 

[wil]

Andy- that was classic!!!!

 

[HerrJeremy]

Sorry for resurecting an old thread, but we spent an inordinate amount of time trying to explain this in CFI ground lab last night, and i'm still a little confused.

I understand that induction lets the loop antenna determine that the NDB is in one of two locations, 180degrees apart. what I dont understand is how the sense antenna diferenciates between them.

 

[F70pilot]

PFM=Pulse

Frequency
and
Modulation

 

[Humty72]

NDB's should be a thing of the past because they DON'T work half of the time. )

yea.. some of you folk may remember this one ...

http://www.myairplane.com/databases/approach/pdfs/05034ND21.PDF

that would take you right for that hill to the N of the approach course..