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Page 1: Radio Nav - Welcome - AirStyle · PDF fileNDB Navaid and ADF Avionics Volume 1 of the Radio Nav series ... Principles of ADF operation 21 Chapter 5: NDBs ... The transmitting antenna
Page 2: Radio Nav - Welcome - AirStyle · PDF fileNDB Navaid and ADF Avionics Volume 1 of the Radio Nav series ... Principles of ADF operation 21 Chapter 5: NDBs ... The transmitting antenna

Radio Nav

NDB Navaid and ADF Avionics

Volume 1 of the Radio Nav series

by Marques Aviation

Edited by

Dr. Pascual Marqués Ph.D.

Published by Marques Aviation Ltd

Southport, United Kingdom TM

Page 3: Radio Nav - Welcome - AirStyle · PDF fileNDB Navaid and ADF Avionics Volume 1 of the Radio Nav series ... Principles of ADF operation 21 Chapter 5: NDBs ... The transmitting antenna

Marketing Director: Elena Spiridon

ISBN 978-1-907980-00-8

Copyright © 2010 Marques Aviation Ltd

Copyright policy

This manual remains intellectual property of Marques Aviation Ltd. All rights reserved. No

part of this manual may be reproduced or transmitted in any form, electronically or

photocopying, without permission from the copyright owner in writing, except for brief

quotations embodied in critical articles and reviews. Permissions may be sought directly

from Marques Aviation Ltd by email at [email protected] or via our website.

Disclaimer

The author has exerted every effort to ensure accuracy of the information presented.

Nothing in this manual supersedes any procedures specified in any operational document

issued by the Civil Aviation Authority or aircraft operators. The information presented is

intended for pilot training only. Updated and approved NDB information should be used for

navigational purposes.

Library of Congress / British Library cataloguing-in-publication data

A catalogue record of this book is available from the British Library.

Published by Marques Aviation Ltd

5, Grosvenor Road, Southport, PR8 2HT, United Kingdom

Tel: 01704 569527

[email protected]

www.marquesaviation.com

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CONTENTS

Page

Introduction 1

Part I – Principles of NDB-ADF operation

Chapter 1: The radio signal 5

Chapter 2: Radio wave propagation 9

Chapter 3: Radio wave modulation 15

Chapter 4: Principles of ADF operation 21

Chapter 5: NDBs around the world 27

Chapter 6: Using the ADF for navigation 33

Chapter 7: Applications - Intercepting track and tracking 43

Chapter 8: Applications – Position fix 53

Chapter 9: The NDB approach and holding pattern 61

Chapter 10: NDB range and ADF accuracy 73

Part II – Multiple-choice questions

Questions 83

Part III – Practical exercises

Exercises 145

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INTRODUCTION

The NDB-ADF navigation system

Radio direction finding (RDF) is a traditional navigational technique that involves obtaining

the direction of a radio transmitter. The oldest RDF navigational aid (navaid) still in use in

aviation is the non-directional beacon (NDB). The principle of NDB navigation is simple and

consists of two parts. An NDB, or ground station facility, transmits radio signals in all 360°

azimuth directions and an automatic direction finder (ADF) receiver on the aircraft detects

the direction of the incoming signals. The term non-directional is counter-intuitive but, in

truth, no specific direction is defined. The transmitting antenna consists of either a single

mast or a long aerial suspended between two masts. The conventional ADF receiver

comprises a loop plus sense aerial system, a control panel, and an azimuth card and rotating

needle display in the instrument panel (Figure 1). The needle automatically and

continuously points towards the NDB station selected for navigation. By turning to the

direction indicated by the ADF needle the aircraft ‘homes’ to the station and it will

eventually fly over the beacon. Originally, the ADF was known as radio compass because the

needle is superimposed on a compass rose. The compass card is graduated in 5° azimuth

increments from 0° to 355°. In earlier days, the loop antenna was an actual metallic loop

mounted beneath the fuselage and enclosed in an egg-shaped fairing. The loop had to be

rotated manually by the navigator to find the direction of the transmitter. In older aircraft,

the basic design of the sense antenna consists of a long wire mounted from cabin roof to tail

fin. In modern aircraft, both the loop and sense aerials are arranged in a single streamlined

housing mounted near the aircraft centreline under the fuselage. The loop antenna is

coupled with a goniometer that determines the direction of the station. The fundamental

ADF instrument is the relative bearing indicator (RBI). An RBI displays the bearing of the

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beacon relative to the aircraft’s nose, thus relative to the aircraft’s magnetic heading shown

in the heading indicator. Visualizing the situation with an RBI can be, at first, daunting.

Figure 1: The NDB transmitter and ADF avionics

The NDB is primarily a short-distance navaid. However, in many parts of the world the NDB

provides navigational aid for long-distance en-route tracking. The NDB enables the pilot to

track to or from a ground station, to determine aircraft position (to obtain a fix), to take

delaying action by entering a holding pattern and to perform an NDB letdown in instrument

meteorological conditions (IMC) or at night. IMC conditions involve limited visibility in poor

weather and low ceilings. An NDB letdown is a non-precision instrument approach to an

airfield, thus an approach assisted by lateral course guidance but characterised by the

absence of glideslope vertical guidance. NDB-ADF navigation suffers from the same signal

disturbances common to amplitude modulated (AM) radio broadcasting which influence the

promulgated range of the beacon and the accuracy of ADF indications.

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To convert magnetic bearings to true bearings use either TB = MB + east magnetic variation

or TB = MB - west magnetic variation. True line of position from the NDB station (coded as

QTE) is used to obtain a position line from the station to the aircraft on an aeronautical

chart based on QDR. QTE is in fact the reciprocal of TB to station. East variation is added to

QDR and west variation is subtracted. In the UK magnetic variation is west, for example QDR

105 - 4° west variation = QTE 101, which is the reciprocal of TB = 281°T (Figure 29).

Figure 29: Determination of true heading, true bearing and QTE

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Figure 38: Position fix using two NDBs

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Chapter 3: Radio wave modulation

Q28 The designation for an on-off keyed carrier is ________ and that for a keyed

amplitude modulated carrier is ________.

a) NON, NON A2A c) NON A2A, NON A1A

b) NON A1A, NON A2A d) A1A, A2A

Q29 Beating is caused by the ________ and________ interaction between signals of

________ frequency.

a) constructive, destructive, different

b) constructive, destructive, equal

c) modulated, constructive, different

d) modulated, constructive, higher

Q31 A beat frequency of 1.4 kHz is produced when the BFO is set to 420.5 kHz. What is

the frequency of the NDB?

a) 419.1 kHz b) 1.4 kHz c) 420.5 kHz d) either 419.1 kHz or 421.9 kHz

Q32 An NDB radio wave has a frequency of 630.5 kHz. To obtain a beat frequency of

2.1 kHz, the two possible BFO frequencies are

a) 628.4 kHz and 632.6 kHz c) 630.5 kHz and 632.6 kHz

b) 2.1 kHz and 630.5 kHz d) 628.4 kHz and 630.5 kHz

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Q102

Q103

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ANSWER - Exercise 10

Current heading is 280. To intercept track 295 (radial 115) using an intercept angle of 45°

the aircraft alters heading to 250 (295 - 45°; aircraft 2). As the aircraft flies towards the

interception point, the RMI needle falls gradually towards MB 295. Just before reaching MB

295 the pilot turns right on heading 295 and flies inbound (aircraft 3). In a crosswind, due

allowance for expected drift would be required in order to maintain a constant track.

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GLOSSARY

A

Abeam Direction of the NDB station off one

wing tip at 90° degrees to the aircraft

longitudinal axis.

Aeronautical chart Map designed to assist in

air navigation that includes topographic

features, hazards, obstructions, navaids,

routes, designated airspace and airports.

Aeronautical Information Publication

Manual containing regulations and

procedures of a lasting character essential to

air navigation.

Airway Route in the air laid out between

navigational aids, such as NDBs and VORs.

Alternating current Electric current that

periodically reverses its direction of flow in a

back-and-forth motion.

Amplitude modulation Modification of the

amplitude of the carrier wave to convey audio

information.

Antenna Metallic wire or rod that radiates or

receives electromagnetic energy.

Approach plate Chart that provides a

graphical representation of instrument

approach procedures including radio

frequencies of the constituent navaids, course

headings, waypoints, altitudes, minimum

visibility requirements, communications

information and a sketch of the airport.

Area Navigation Navigation method under IFR

that permits the aircraft to follow any course

within a network of navigation beacons by

removing the need to fly directly to or from a

navaid.

Attenuation Weakening of a radio wave as it

travels over the ground or sea surface

(groundwave) or enters an ionospheric layer

(skywave).

Automatic direction finder Equipment on the

aircraft that detects the direction of the

incoming radio signal transmitted by an NDB.

Azimuth Horizontal angle in degrees

measured clockwise from north as reference

datum.