Expert: Marc Ebelini - 3/8/2009

Question
QUESTION: why ndb is non-directional and not omni-directional, when both transmit in all direction.

ANSWER: Is this a quick question? Non directional and omni direction are the same thing. If it is omni it means in all directions. Non directional means it can go in any direction so what is the difference? If it is directional then it is not omni directional. It's like the glas is half full or half empty, they are the same. Hope you understand? Maybe you stated the question wrong?

---------- FOLLOW-UP ----------

QUESTION: its something concerned with uniform in one plane, I couldn't understand that. OR what is the difference between them OR why NDB IS called non-directional and not called omni-directional. This is the question I got in an interview and I couldn't explain the difference b'coz both transmit in all direction

Answer
It was a poor question because the writer knew what he was talking about but did not phase it properly in my view. Must assume he was writing about Omni range navigation (VOR) verus beacons. A beacon transmits in all directions for vessels or aircraft can home in on. Could be manual or automatically pointed to that stations location. Normally called an ADF (Automatic Direction Finder) where as the Omni range always lets you select a radial of your choice to home in on. Technically the omin range transmits two signals, one is omni direction and the second one is analog and is sent directionally rotating at 1800 RPM. The phase angle is measured between the omnisignal and the rotating directional signal to determine which radial you are located on. This phase angle is measured is in a way that allows you to see if you are flying to or away from the station.
As you can see the question was misleading because the Omni range is also directional when transmitting the analog signal. The reference signal is omni directional and is FM and is used to start the search at zero degrees magnetic. Now does this all make sense to you?