Same thing as an NDB, just a differentname. When a nondirectional beacon is co-located with the outer marker of an ILS system, it’scalled an "outer compass locator" or LOM. Some NDBs also broadcast voice,often transcribed weather.
FLIGHTGEAR RADIO TUTORIAL CODE
Aviation NDBs have a two- or three-letter identifierbroadcast in morse code at an audio frequency of 1020Hz. Most ADFs also receive the standard AMbroadcast band at 550-1600 Khz. Nondirectional beacons foraviation use broadcast between 200-415 Khz. The tuning knobs let you select the desired NDB frequency. A slaved compass card is expensive, but sure makes it a lot easierto fly an ADF approach. The compass card may be fixed,manually rotatable with a knob, or (in more expensive RMI systems) slaved automatically tothe aircraft heading. The needle points to thestations when the receive is in "ADF" mode.
The ADF indicator consists of a needle and a compass card. If it doesn’t, then thisfunction is usually activated by switching to "ANT" mode. If your ADF is has a "TEST" button, this should cause the needle to slew tothe 90-degree position whenever the button is pressed and held. This featureis is seldom used in the United States except for a few marine beacons, but can be veryuseful when flying in other parts of the world. "BFO" stands for "beatfrequency oscillator" and what it does is to generate an audio tone to let youidentify beacons that identify themselves using interrupted-carrier keying. In the "ADF" mode, the pointer is activated and the ADF tries to point to thestation. On King ADFs, the needleshould park in the 90-degree position when the receiver is in "ANT" mode otherbrands may work differently. This mode provides the clearest audio reception, so you’dnormally use it to identify a station or listen to Rush Limbaugh. If the"ANT" mode is selected, the loop antenna is disabled and all receiving is donethrough the sense antenna. Most ADF receivers have several modes that the pilot can select. By the way,these antennas typically cost $800.00 so go easy on them when cleaning or moving.
FLIGHTGEAR RADIO TUTORIAL INSTALL
The combinedloop/sense antenna usually goes on the bottom because it’s easier to install there, and ifyou forget to lower your gear, it will be the first thing to get ground away.
FLIGHTGEAR RADIO TUTORIAL PLUS
It works far better than the oldsystems, plus it has less drag and is much less vulnerable to icing. More recent ADFs have a combined loop/sense antenna. (On larger aircraft, the sense antenna may be located on thebottom of the aircraft.) The loop antenna is a flat antenna usually located on the bottom of theaircraft, while the sense antenna is a long wire that often runs from top of the tail tothe top of the of the cabin. With the older ADFs, they are twoseparate antennas. The ADF can tell from the loop antenna signals that the NDB is one of twopossible directions, 180 degrees apart, and the sense antenna lets it figure out which ofthe two is correct.Īll ADF systems have loop and sense antennas. In addition to the loop antenna, all ADFs have another antenna called the senseantenna. (We could go into the sine and cosine theory here, but who really cares aslong as it points to the proper direction?) Two antennas By measuring thephase difference between these two windings the ADF is able to determine the direction ofthe beacon. The loopantenna consists of two perpendicular windings on a square ferrite core. The H-field induces a voltage into the windings of the ADF loop antenna. NDBs transmit a vertically polarized wave which means the E-field is vertical andthe H-field is horizontal. These fields are perpendicular in space, and their amplitudes vary sinusoidally withtime. (Why isn’t the magnetic field called the M-field? Nobody seemsto know.) The radio waves from an NDB consist oftwo electromagnetic field components: an electric field called the E-field and a magneticfield called the H-field. It’s easier for me to explain to my wife why I was seen out with a redhead than toexplain how the ADF works but I’ll give it a shot. Yet believe it or not, the ADF is one of the most complicated avionics systems inour aircraft. The purpose of the ADF is to point to a non-directional beacon and that is the onlypurpose.
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