Radio Stations. Installation, Design and Practice

272 Pages·1959·19.31 MB·English

by  G. A. Chappel, D. W. Fry and W. A. Higinbotham (Auth.)

RADIO STATIONS
INSTALLATION, DESIGN
AND PRACTICE
By
G. A. CHAPPEL
A . M . ( S . A . ) I . E . E . , A . M . B R I T . I . R . E . , A . M . INST.E.
P E R G A M O N P R E S S
L O N D O N · N E W Y O R K · P A R I S · L O S A N G E L E S
P E R G A M O N P R E S S L T D .
4 & 5 Fitzroy Square, London, W . l
P E R G A M O N P R E S S INC.
122 East 55th Street, New Y o r k 22, N.Y .
P.O. Box 47715, Los Angeles, California
P E R G A M O N P R E S S S.A.R.L.
e
24 Rue des Écoles, Paris V .
Copyright
©
1959
G. A. C H A P P E L
Library of Congress Card No. 59-9614
Printed in Great Britain by Wyman and Sons, Ltd., London, Fakenham and Reading
P R E F A C E
THE object of this book is to discuss various methods which are
employed in planning and designing radio stations. Inevitably, this
subject embraces a very wide field, and it would be difficult indeed
to include, in one volume, every possible aspect of radio station
installation design, for the range and scope are enormous. As a
result, a considerable part of this book embraces small station
design, since they are in the majority throughout the world.
Nevertheless, much of this work is applicable to stations irre-
spective of size or power, since the general conventions remain
basically the same.
There is a distinct lack of co-ordinated information on the subject
matter of this work available on the general market and it is the
sincere hope of the author that he has made a useful contribution to
this fascinating branch of engineering.
G . A. CHAPPEL
Nairobi,
Kenya.
vii
A C K N O W L E D G E M E N T S
The author gratefully acknowledges his indebtedness to the following
manufacturers, who so willingly and freely furnished photographs,
line drawings and data concerning their products :
AUTOMATIC TELEPHONE & E L E C T R I C C O . , L T D .
AUSTINLITE L T D .
LAMSON ENGINEERING C O . , L T D .
MARCONI'S WIRELESS T E L E GRAPH C O . , L T D .
MARCONI INSTRUMENTS L T D .
N O R S K MARCONI KOMPANI
P Y E TELECOMMUNICATIONS L T D .
T H E PLESSEY C O . , L T D .
PYROTENAX, L T D .
STANDARD TELEPHONES & CABLES L T D .
Especial thanks are due to D R . T . G. HAMMERTON who so kindly
encouraged the author to write this book, for his helpful suggestions
and for checking the manuscript.
viii
INTRODUCTION
General
THE planning, design and installation of radio stations comprise a
most fascinating branch of radio engineering, offering much scope
for ingenuity to the engineer.
The finished station must be so arranged that optimum equipment
performance is secured; at the same time, by judicious design and a
sensible layout arrangement, the routine tasks of operator and
maintenance technician alike should be facilitated. These require-
ments may be satisfied only by careful planning in the initial stages
of the design, and by employment of modern ideas and equipment.
Types of station
In large stations, it is usual to engineer the radio equipment so
that transmitters and their associated power supply equipment are
arranged side by side.
When dealing with very high power, it is often necessary to arrange
the transmitter elements in sections, thus, taking the case of a high-
power broadcast transmitter, say, in excess of 250 kW output
capability, the stabilized drive and penultimate modulator units
may be fitted into racks adjacent to the main hall. The main hall
would contain all r.f. equipment and final modulator valve unit,
whilst the modulation transformer and power supplies would be
arranged either in a hall adjacent to the main hall, or immediately
below, according to convenience.
At the other end of the scale, small stations featuring low-power
transmitters are often installed adjacent to the operating position
which, in the case of very low-power transmitters, may be a common
room.
Small stations are to be found performing various tasks, from
small point-to-point v.h.f. links serving business organizations, taxi
services, civil aviation organizations, fire, police and similar depart-
ments, to local broadcasting services. With the exception of broadcast
1
2 I N T R O D U C T I O N
services, the principle common characteristic shared by most small
stations is that of intermittent transmission, although reception may
be a continuous requirement.
An enormous number of these small stations are installed in
various parts of the world. In certain countries, particularly in
under-populated territories, the distances covered are vast and it
quite often happens that alternative communication facilities are
restricted. In such territories, we may find small stations which
are employed for international telegraph or telephone services by
day, and local broadcast duty, on a regional basis, by early and late
evening. The public telephone services are often routed over v.h.f.
multiplex circuits, or have such a system as a standby to the main
overhead telephone line.
The general tendency at present is for manufacturers to produce
transmitters in one unit, or within a single enclosure, so far as
possible, rather than in separate units as was the older practice.
Radio receivers may consist of the well-established tuneable
versions or, where one or more fixed frequencies are dealt with, either
a bank of single channel crystal controlled receivers are installed or,
if desired, several switched channel receivers may be employed.
The current trend is to produce tailored installations, to suit
individual needs. Such installations make it possible for the station
to be commissioned with the least expenditure of highly skilled—
and consequently expensive—man hours on the site.
Standardization of plans
Wherever more than one installation of one type design is to be
installed, it is distinctly preferable to establish a standard set of
plans. This will save much time and trouble in the long run.
Accommodation of the equipment
Unlike the larger stations, the small station almost invariably
has to be fitted into an existing site. This state of affairs is particu-
larly applicable in the case of small aerodromes where either an
economic installation is made within the terminal building, where this
is physically associated with a control tower, or in a building adjacent
to the control tower, the relative distances between being determined
by a variety of factors, each of which is dealt with under its chapter
heading.
I N T R O D U C T I O N 3
Similarly, communications equipment for administrative control
often has of necessity to be engineered adjacent to, or even within,
existing offices which, in town, is apt to present specific problems.
Yet a further situation arises where existing buildings require to
be converted to house the equipment.
Special considerations
Under certain circumstances, in particular territories, the desir-
ability of ensuring the minimum possible run of underground cable
and the virtual exclusion of overhead lines for control purposes is
dictated, greatly, by the degree of honesty of the populace in the
near vicinity of a route. Such a situation, whilst rarely arising in
modern highly-developed countries, is a very real factor which must
be taken into account in certain under-developed territories.
The operating position
The importance of providing adequate and suitable faculties for
the equipment operator is one often overlooked, but one which
imposes a very real demand on the conscientious designer.
The object is to fulfil the following general requirements:
(a) The equipment must be reduced to a minimum, in order to
facilitate ease of handling, without being too austere or,
conversely, over cumbersome.
(b) Efficient operation must be the keynote of the layout.
(c) It will be realized that efficient traffic handling may only be
obtained by ensuring the utmost freedom from fatigue of the
operator.
(d) Any signals message distribution scheme employed should
be such that the operator does not have to rise from his seat,
but should be arranged to fall within the radius of his arm,
when seated comfortably—though of course, not relaxed.
(e) The minimum number of physical movements must be em-
ployed, together with the minimum number of operational
functions to operate the equipment. Footswitches for actuat-
ing the equipment should be employed whenever the demand
arises.
(f) All control equipment must be positive in action, strictly
functional, and not over-complicated.
4 I N T R O D U C T I O N
(g) Lighting should be adequate and efficient.
(h) Ventilation and heating, where required, must be adequately
provided for. The efficiency of the operator will depend to
a surprising degree on attention to such detail.
(i) The overall layout should be so arranged that the speedy
exchange of equipment may be facilitated, without the
servicing technician having recourse to interrupt the operator,
if it can be avoided in any way, or without causing a major
disruption of services.
The transmitting position
What has been stated for the receiving position also holds good,
generally, for the transmitting position, with particular emphasis on
accessibility.
Unless the transmitting equipment be accessible, then not only
is the possibility of speedy servicing and inspections precluded, but
the minimum disruption to services cannot be achieved.
Cramped conditions are not conducive to safety of servicing
personnel.
Similarly, inaccessibility invariably results in very rapid fatigue
being experienced by the servicing personnel. Nothing is worse than
if one has to crouch at the rear of a transmitter for extended periods,
sandwiched between the equipment and an adjacent wall.
Special emphasis must be placed on the necessity for adequate
lighting, both natural and artificial, not only for use during normal
adjustment to equipment but also to ensure that an adequate lighting
intensity is available during servicing of the equipment. Much
economy may be effected by employing suitable paint finishes to the
building interior.
By day, this condition may be satisfied by correct positioning of
windows and roof lights, whereas, by night, the ideal arrangement is
to ensure that wall-mounted bulkhead lighting fittings be so arranged
that the minimum shadow is cast. These should be supplemented
by provision of a mains outlet socket for the plugging in of an
inspection lamp, such sockets being installed in the ratio of one
between every two transmitters or items of major equipment.
The above factors are equally important, whether the installation
be for a single piece of equipment or a multiple installation.
I N T R O D U C T I O N 5
Planning a station layout
When planning a layout, it is advisable to experiment with a mock-
up of the actual station, if possible.
For small installations, either single or multiple, the actual
equipment may be set up in a convenient place, using chalked
boundaries, if necessary, to approximate to the actual physical sizes
which will be met on site. One receiving position and one transmitter
will be required, for each type proposed. This effort invariably
results in a very well-planned, economic layout. Models or wood
patterns may be made up, to a common scale of size, if desired.
A cheaper method—and one which has to be used for the larger
equipment installations—is to use squared paper. Surprisingly,
relatively little use is made of this system and it is felt, therefore, that
some comment on the method of use will not be out of place.
Having determined the size of accommodation available, the next
step is to obtain a supply of graph paper. This should be printed in
1 in. squares, graduated in twelfths where British units of measure-
ment are employed, or tenths in the case of the Metric system.
The selection of a suitable scale will, of course, be determined
by the size of the layout required, but, as a general guide, the scale of
1 in. = 1 ft. will be found suitable for the majority of needs.
The next step is to cut, from a similar sheet of graph paper a
floor plan of every single item of equipment proposed for the installa-
tion, to the same scale as that already chosen for the building
accommodation.
These may then be placed on the floor plan and arranged intelli-
gently to give the best possible layout.
In installations where servicing workshops, stores, engine-driven
power plant, etc., are proposed, then, having determined the eco-
nomic sizes for each room, the main plan may be marked in pencil
to show the selected positions of each item of equipment, bench, desk,
shelves, etc., and the plan cut up, by rooms, thus permitting experi-
mental arrangement of the different sections of the building to be ob-
tained—often with improvements resulting over the original layout.
It should be borne in mind that the cost of the building will be
minimized if the rooms are chosen to be of a standard width for the
plan being examined and a straight run employed.
The requirement of other than simple roof designs invariably
enhances the cost of building enormously. Moreover, unless one is
6 I N T R O D U C T I O N
particularly careful with the planning of such a layout, there may
be severe limitations imposed on the extension of the building at a
later date, should this be desired.
Having determined the ideal layout, the next stage is to draw out
the site plan, employing squared paper as before, and drawing thereon
the building plan outline, together with any features already existing
at the site, inclusive of boundaries. The relative siting of the building
will be dictated by many factors, all of which are dealt with in the
following chapters.
Having selected the desired aerial and earth systems to suit the
requirement, the masts and/or towers may next be drawn on the site
plan.
It very often happens that, owing to site restrictions, several
attempts may have to be made before a satisfactory arrangement is
arrived at. This may even necessitate a slight re-arrangement of the
equipment within the building.
It is not a good convention to make the arrangement of aerial
systems subservient entirely to the restrictions of a site and, under
certain conditions, it may even be necessary to review the availability
of alternative sites, for the efficient performance of each aerial
system is as important as the equipment which it serves. Moreover,
the possibility of expansion at a later date must be remembered,
equally as in the case of the equipment building.
Economically, the attainment of a gain of the order of several
decibels may often be conferred to the installation by relatively small
expenditure on the aerial systems. This naturally dictates the
minimum possible site restrictions for the aerial systems.
On the other hand, however, the attainment at the transmitter
of an output increase of even 5 dB over the existing power output
capability may incur considerable expenditure, as compared with
the capital cost of the initial installation, since not only will the
fitting of a larger equipment be demanded but also relatively ex-
pensive additions for mains power supply, standby power plant, etc.,
may require to be entertained. This increase is found to be propor-
tionately greater as the transmitter power increases.
It will be evident that there is both a technical and practical
limit to the degree to which aerial systems of increasingly higher gain
may be employed, but consideration is demanded to a careful analysis
of the problem in each case.