"The more things change, the more
they stay the same," applies to many things, and certainly does for crowding
issues in the electromagnetic spectrum. Just as with a gas in an expanding
volume, uses for newly opened regions of the radio spectrum are quickly occupied
by new users. From the beginning of the radio age, the ability to utilize higher
and higher frequencies was limited only by available technology - first vacuum
tubes and now semiconductors. Now, as then, it is the higher power transmitting
side of the communications equation that governs the upper frequencies.
Designing components which work both at high frequencies and high powers is much
more difficult than designing for lower powers. Capacitance, inductance,
electron travel times, and voltage breakdown barriers are the culprits. This
1945 article from Radio News magazine discusses some of the issues which needed
to be overcome in order to expand television broadcasting comfortably into the
UHF region. Many industry forces were behind the push in order to open new
markets and to squeeze more revenue-producing programming into existing spaces.
Somewhat unexpectedly, the advent of cable television (CATV) thwarted well-laid
plans for over-the-air broadcasting, and as history shows, UHF languished in the
shadow of cable.
The Future of U.H.F. - The u.h.f. region will become of utmost significance
in providing channels for many miscellaneous services.
This Cullercoats coastal radio station will be converted to the
ultra-high frequency operation of maritime radio beacons immediately postwar to
insure greater safety for ships and trawlers in fog and darkness.
By A. Leon Laden
Looking at the electromagnetic spectrum chart comparatively simplifies the difficult
task of forecasting with any reasonable degree of accuracy the role the higher frequencies
are destined to play in the future. It shows the saturation reached in the traditional
regions of the radio spectrum and indicates that any future expansion must logically
proceed along stereotyped lines and follow the same upward course in the utilization
of the metric, centrimetric and millimetric bands as was followed previously in
the exploitation of the long-, medium-, and short-wave bands.
Moreover, the u.h.f. and microwave bands are ideally suited to meet the channel
space requirements for the progressive relocation of existing familiar radio services
congested on lower bands and the accommodation of legitimate new services without
jeopardizing the scope or volume of tomorrow's brand-new services.
Conditioned by improvements in equipment and developments in operating techniques,
infiltration into these bands will provide many times more frequency channel space
than used at present by all the radio stations in the world or needed for some considerable
An idea of the prolific fertility of the meter and decimeter bands alone can
be gathered from the fact that the span of frequencies extending from 30,000 kc.
or 30 megacycles, corresponding to 10 meters, down to 3,000,000 kc. or 3,000 megacycles,
corresponding to 10 centimeters, can accommodate the enormous number of 297,000
stations at the present rate of elbow room assigned to broadcasting stations on
This Port Patrick coastal radio station, erected in 1937, was
the first in England to apply commercial u.h.f. multiplex radio-telephony.
But even the frequencies contained in the ultra-high-frequency band, which can
be defined as stretching from 30,000 kc. or 30 megacycles to 300,000 kc. or 300
megacycles or, expressed in wavelength, from 10 to 1 meters, is impressive enough
and can yield 1485 channels, each 200 kc. in width, for frequency modulation or
49 channels, each 6 megacycles in width, for television.
Nonetheless, the distribution of frequency bands for use by various services
between various countries is extremely complicated and the devising of workable
schemes of frequency allocation is not solely governed by mounted radio progress
in the sparsely-occupied or barren regions of the electromagnetic spectrum.
Apart from a variety of technical considerations it must, necessarily, depend
to a large extent on international good will and co-operation.
The very-short waves are neither as immune from interference nor as limited in
radiation as sometimes assumed.
Studio control room in the BBC's television station, London.
The effects of diffraction and ionospheric refraction can extend the service
areas of transmitting stations operating on quasi-optical wavelengths enormously
by returning signals to earth at distances up to thousands of miles.
(It is claimed that prewar BBC television transmissions radiated on a carrier
frequency of about 40 megacycles, i.e. 7 meters in wavelength, from the London station
covering nominally an area of some fifty miles, were received in South Africa and
in the middle of the United States.)
But even on purely optical frequencies quickly absorbed by the water and carbon
dioxide in the air, some international agreement will be necessary to avoid severe
interference from radar, navigational, industrial, and similar equipment.
Undeniably, therefore, the distribution of frequency bands in Europe, based on
the allocations as revised at the International Telecommunication Conference held
in Cairo in 1938, is totally out of date and inadequate, as no provision was made
at the time for police, aeronautical, radio beacons and direction finders, frequency
modulation, or facsimile (which all have a place in the allocations agreed upon
at the Santiago Conference in 1940 for use in the Americas).
Before the war, too, only the U.S.A., England, France, and Germany ran television
services and the exploitation of u.h.f. for broadcasting, communication, and other
services was very limited in scope of application.
It is reasonable to expect wartime radio progress to have contributed, moreover,
materially towards enhancing the prospects of various countries claiming u.h.f.
allocations for stations post-war, especially since a huge radio-engineering capacity
will be available and skilled labor awaits employment.
BBC's omnidirectional vision transmitting aerial array.
No one can, of course, prophesy future development but it can be envisaged that
the internationally constituted governing body which will be set up at the next
Telecommunication Conference to lay down requirements of radio governance throughout
the world on a revised basis is bound to favor a framework of u.h.f. allocations
schemes integrated as a constituent part into a general worldwide radio organization.
The vast spectrum area will be re-planned and subdivided and radio services moved
about as pawns on a chessboard to balance within the great pattern of a master plan.
To facilitate discrimination, frequencies will probably be allocated in separate
latitudinal and longitudinal bands on a global scale to countries grouped into regional
zones bounded by natural and geographical limits.
Certain specifically defined groups of frequencies may well be reserved for international
traffic and assigned to geographically-spaced-out, internationally-controlled, fixed
units located in "free zones" or international civil aviation centers for operation
on shared basis. Such an arrangement would ensure, throughout the world, standardized
navigational aids, airport control, services for aircraft in flight, radio beacons
and direction finders, press traffic, and certain other services.
Another group of frequencies might be assigned to fixed stations catering for
countrywide distribution and include military, governmental, broad-casting, communication,
and other services designed for internal consumption.
Yet another group of frequencies could be allocated to fixed or mobile units
for services exclusively restricted to local needs such as county, educational,
police, fire, alarms, etc., making it possible to repeat channel assignments at
close distances permitting more stations to operate on fewer radio channels.
U.H.F. and FM Broadcasting
The spectrum utilization chart, reproduced through the courtesy
of the British Institution of Radio Engineers, amply evidences the saturated state
of the traditional frequency regions. It also indicates that progressive radio and
electronic development is bound to necessitate increasing infiltration into higher
bands and inaugurate the era of the ultra-short-waves. The wavelength units indicated
are meters, centimeters, millimeters, microns (μ), and angstroms.
Shared channel working is bound to facilitate multiplication of channels for
ultra-high-frequency services comprising sound, vision, and other complementary
or independent services in their initial stages of development.
High fidelity FM sound services reducing the level of every type of interference
and providing noise-free and static-free reception will form an integral part of
these u.h.f. services and replace in time common types of modulation.
Programs will be transmitted from stations with power outputs ranging from 50
kilowatts down to 5 kilowatts giving coverage over considerable distances free from
mutual interference and overlapping between stations, the actual range, of course,
depending on the nature of the terrain.
For example, Great Britain and Northern Ireland will probably have about twelve
stations, separated on the average by less than 150 miles, to cater for the London
and more populous districts in the Midlands and Northern and Southwestern areas.
Distribution to areas with dense populations will be by coaxial cable networks
giving shorter maximum operating range than broadcasting stations on standard wavelengths
but improved signal-to-noise ratios.
To reduce program cost-per-listener and extend territorial coverage to less populous
areas, however, closed line distribution will be discarded in all probability as
too cumbersome and expensive (coaxial cable costs about $10, 000 a mile to install)
and open aerial transmission used instead. In the course of time, this twin system
of diffusion will assume countrywide proportions ensuring almost 100 per cent coverage.
Reception of FM programs will take place on low-priced automatic frequency-controlled
sets of increased dependability and performance efficiency but decreased in size,
containing a minimum amount of metal and fitted with a series of tube devices, brought
down from the academic to the mass-production level, governing oscillation and amplification
to a much greater degree than possible with conventional tube structures .
Cabinets will be made of smooth-faced, highly polished plastics without sharp
corners and knobs laying flush with the streamlined body.
But the introduction of FM will not necessarily make obsolete conventional type
sets; wavelength converters will enable such receivers to operate on the higher
Television will undoubtedly present a far more difficult problem than u.h.f.
and FM broadcasting as very wide sidebands are essential for fidelity in the reproduced
picture and the width of the band that can be transmitted increases as wavelength
It may be anticipated, therefore, that the keynote of the television services
of the future will be interchangeability. Related to the transition characteristics
of the heights and densities of the ionized layers altering under the influence
of solar radiation, such services will be capable of short-, medium-, or long-distance
operation throughout the space of the year, irrespective of erratic conditions with
525-line monochromatic services operating below 100 megacycles will probably
be established first of all as part of the countrywide u.h.f. networks; the video
portion of the distribution system connecting subscribers living in blocks of flats,
housing estates, dormitory suburbs, and built-up areas directly with the transmitting
stations as well as distributing to the remoter rural areas in the same way as the
audio portion of the network.
The pattern of future television developments, however, will be determined by
migration to higher frequencies called for by the lack of adequate channel space
and the requirements of improved services of wider video bandwidth for color television.
John L. Baird's facsimile television apparatus,
his latest invention, consists of a spool holding a roll of sensitized cinematograph
film which is passed continuously in front of a gate upon which is focused the image
of the television pictures reproduced upon the screen of a cathode-ray tube. Pictures
are reproduced at the rate of 25 per second and each picture is thus photographed
upon the continuously-moving film in 1/25th of a second. At the right is shown the
first photograph transmitted by this equipment. It is made up of 200 lines; however,
the number of lines can be increased to produce any desired picture quality.
The 300-500 megacycles or 500-1,000 megacycles regions will probably ultimately
become the permanent home of television with definition of order of 1,000-1,500-lines,
vision bandwidth up to 20 megacycles and the transmission of audio and video signals
on the same wavelength.
Multipath distortion of pictures in transit, secondary images, and other "ghosts"
will be eliminated completely as transmissions on these frequencies will be too
high to be refracted by the ionospheric layers or interfere with other stations
on same channels.
The practical difficulties associated with efficient operation with sufficient
power output on increased frequency bands and the different conditions of propagation
will involve the abandonment of single-area coverage from high-power transmitters
and their replacement by several low-power stations fed by large numbers of substations
Dissemination of the large, clear, steady, detailed, all-electronic pictures
radiated from these stations will take place without diffusion over the air by direct
or line-of-sight reception on communal aerials distributing over local coaxial-cable
networks of rigid frequency characteristics without attenuation of the very broad
In time, the cloak of mystery enveloping the upper regions of the atmosphere
will be torn away revealing the structure and properties of the Kennelly-Heaviside,
Appleton, and various other ionized layers. Means will then be found to use the
ionosphere as a transmission medium in all its moods. This, in turn, will make possible
the setting up of a long-distance television service.
Such a service could operate around 1,500-2,000 megacycles and maintain perfect
synchronization at the receiving end thousands of miles away at high rate of frames-per-second,
providing 2,000-line interlaced, broadband multicolor pictures with much higher
definition than at present.
New television receivers will be manufactured in quantity and put into the hands
of the public at a fraction of the previous cost due to standardization of components
and important developments in simplifying equipment.
Diagram for British u.h.f. services, illustrating the way in
which two British radio engineers propose to cover the populous areas of Great Britain
and Northern Ireland with 12 stations, so placed that three separate carrier frequencies
would suffice for television and FM services. The frequency bands to be used for
various regions are distinguished on the map by different shading.
Progress in the cathode-ray tube manufacturing art will bring down the price
of these tubes to a few dollars (before the war, cathode-ray tubes cost about 60s
in Great Britain; their present cost is about 20s); production facilities and improved
workmanship making coaxial cables cheaper and more efficient.
Relaying is a relatively old branch of radio which in its various modern applications
will undoubtedly play an ever-increasing part in tomorrow's u.h.f. network systems.
Relay units will be called upon to fill the gap wherever line coverage of aural
and visual signals will be impracticable, uneconomical, or unreliable.
These units will consist of strategically-located substations deriving power
from public supply mains or independent Diesel electric power plants employing high-towered
aerial arrays for local distribution of programs. Associated with them, satellite
installations of unattended and battery-fed amplifying equipment will effect point-to-point
transmission along defined routes without wasting a large part of power in indiscriminate
To minimize interference between transmitting and receiving signals, different
carriers will be used and the plane of polarization of the waves emitted by the
transmitting section of the aerial will be at right angles to that of the waves
received by the receiving section of the aerial.
On occurrence of a breakdown in any part of such a unit, spare apparatus will
be brought automatically into operation and a fault signal given to a central remote-control
The manifold possibilities of relaying will be recognized in time, adding a powerful
tool to ultra-high-frequency utilization.
Conditioned by physical and geographical factors, u.h.f. relaying will, at relatively
small expenditure, gradually be extended to span continents linking-up with a worldwide
system of radio girdling the earth.
This will make possible regular transoceanic transmissions hooking up Europe
with other continents by the aid of remote-controlled relay units either anchored
to the ocean-bed or afloat but self-propelled to maintain a defined position.
Single-network world coverage would thus be provided, effecting great" economy
in radio spectrum utilization.
Within the worldwide framework, monitoring stations will be set up to relay automatically
field strength recordings and propagation prediction with stations forecasting reception
conditions well in advance on the basis of round-the-clock observations of ionospheric
variations while statistical tables of the 11-year sun-spot activity-cycle will
assist in correcting any marginal errors that might occur.
One of the British General Post Office's rotating arrays, illustrating
the straight-forward construction of a beam antenna. It is part of the Leafield
radio stations' telegraph transmitter, operating around 28 megacycles or about 10
Block diagram showing typical general arrangement of an automatic
radio relay station.
Circuit diagram of combiner and recording unit.
Courtesy Cable & Wireless
Ltd., London, England
Based upon the worldwide relay network and operating on the principle of different
propagation conditions and time differences existing throughout the world, multichannel
ultra-high-frequency communication systems will evolve for use in all cases where
it is desired to transmit signals with maxi-mum reliability and minimum interference.
These systems will enable limited point-to-point communication as well as long-distance
dialing without the intervention of exchanges.
By the use of line-finder equipment, call connections will be effected automatically,
permitting dozens of conversations to take place simultaneously on the same trunk
lines resulting in a tremendous saving of time and labor.
By the application of television principles to photo telegraphy, the fastest
method of picture transmission will become available for the sending of photographs
from point to point and capital to capital with the least amount of delay.
Apart from facilitating picture transmission, the introduction of this new method
on a broadcasting basis will also simplify presentation and distribution of news
and photographs by linking up with visual and aural facsimile services.
Once these new services are grown up and firmly established in the public eye
as reliable media, they unquestionably will provide more receiver hours than frequency
modulation or television and certainly at a far lower cost-per-hour.
Newspapers will undergo a major transformation in format and contents by the
establishment of the novel forms of news dissemination; world-wide daily papers
- the dream as well as the nightmare of every newspaper-man - published simultaneously
in widely separated centers at greatly reduced cost will probably outrival one day
Television, extended to the telephone, will enable visual as well as aural contact
to be maintained at will by the provision of a switch-off arrangement fitted to
Perhaps one of the major u.h.f. utilization offshoots destined to grow into healthy
and indispensable auxiliaries in the future will be in land, sea, and air transportation.
Trains, ships, and planes will be operated, steered, and controlled automatically
along beam traffic lines facilitating all-weather travelling, sailing, and flying
in complete safety.
Prominent among tomorrow's other uses will be medical science; u.h.f.-operated
medical apparatus adding a number of new therapeutic and diagnostic tools to existing
Education will be yet another beneficiary of radio progress affording children
and grownups alike opportunities for study and experience under the most convenient
Radio-frequency heating undoubtedly will infiltrate into the u.h.f. band and
rank high among its users.
U.h.f.-operated systems for taxicabs, buses, automobiles, street-traffic control,
police alarms, fire warnings, and a host of similar safety-of-life or public utility
features, laughed at as freaks yesterday, will be commonplace tomorrow.
Posted July 9, 2021