TACAN (TACTICAL NAVIGATION SYSTEM)

General:

TACAN is a military system combining the bearing capability of VOR with the distance measuring capability of DME

It is also designed to be transportable so that it can be used in combat areas, hence the name tactical

TACAN (TACTICAL NAVIGATION SYSTEM)

Principle:

TACAN is based on DME in that it uses the DME antenna and the DME pulse format.

Thus the distance measuring is inherent

TACAN Bearing Function:

Two concentric drums are placed around the DME antenna

The parasitic elements distort the DME antenna pattern

The drum structure is rotated at 900 rpm (15 Hz)

TACAN Bearing Function:

The resulting pattern has one main lobe caused by the inner parasitic element, and 9 secondary lobes caused by the outer elements

TACAN Antenna Installation

TACAN

Thus the TACAN signal consists of 2700 pulse-pairs/second whose amplitude is modulated by a 15Hz signal and a 135 Hz signal

These constitute the variable part of the TACAN signal

TACAN

The reference part of the TACAN signal consists of coded sets of pulses called reference groups (or bursts)

The MAIN reference group (MRG) consists of 24 pulses with alternate spacings of 12 and 18μs. This is transmitted when the antenna pattern main lobe reference point passes the North reference

The AUXILIARY reference group (ARG) consists of 12 pulses with of 30 μs spacing. This is transmitted when each of the auxiliary lobe reference points passes the North reference

TACAN The lobe reference point is the

NEGATIVE-GOING ZERO CROSSOVER

TACAN RECEIVER

TACANSince TACAN is not a civilian system it does not have to conform to normal aviation requirements

However, since military aircraft use the same airway structure as civilian aircraft, there are TACANS collocated with VORs on most airways. and these conform with the civilian standards for VORs

These facilities are called VORTACs

TACAN