Among the fundamental tools of the navigator are radio navigational aids. There are
numerous types of radio navigational aids which generate such diverse information as position,
bearing, range, and glideslope. All radio navigational aids consist of three essential
a ground facility which transmits electromagnetic waves,
(2) a receiver in the aircraft which interprets the information transmitted by the ground
instrumentation in the aircraft to display this information to the aircrew.
Three radio navaids will be discussed in this unit: ADF (Automatic Direction Finder),
VOR (VHF Omnidirectional Range), and TACAN (Tactical Air Navigation). These radio
navaids will demonstrated or utilized during some phase of the VT-10 flight curriculum. Some
combination of these radio navaids are carried aboard all naval aircraft.
AUTOMATIC DIRECTION FINDER (ADF)
The characteristics of ADF are:
1. ADF's operate in the LF or UHF bands.
Although many new types of direction finding and homing equipment are coming into
widespread use, the automatic direction finder (ADF) remains a basic and important piece of
equipment for homing, tracking and course interception. ADF is a radio receiving system used
to determine the direction of arrival of received radio signals from a nondirectional beacon
(NDB). ADF receivers operate in different frequency ranges and are used in practically all
naval aircraft. In the T-39 aircraft, the ADF systems operate in a segment of the UHF (Ultra
High Frequency) band between 265.0 and 284.9 MHZ. The ADF position on the T-34 UHF
radio does not function.
2. ADF always presents relative bearing information.
If the ADF needle is pointing to the 2 o'clock position, the station bears approximately
60º to the right. If it points to the tail of the aircraft, it bears 180º from the present heading.
When properly functioning, the ADF bearing needle always points to the NDB station.
By adding the relative bearing (RB) obtained from the ADF bearing needle to the
magnetic heading (MH) of the aircraft, a magnetic bearing (MB) to the station can be
determined, RB + MH = MB (Figure 1).
RADIO AIDS TO NAVIGATION