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"F-M" Put on Commercial Basis August/September 1940 National Radio
Aug/Sep 1940 National Radio News
of Contents] These articles are scanned and OCRed from old editions of the National Radio Newsmagazine. Here is a list of the
National Radio News articles I have already posted. All copyrights are hereby acknowledged.
Edwin H. Armstrong demonstrated the viability of FM
(frequency modulation) for long distance
broadcasting in January of 1940, the U.S. FCC
(Federal Communications Commission)
allocated spectrum to it in the 42-50 MHz band. Armstrong had
introduced the FCC to FM originally in 1936. The new modulation
scheme was popular due to its immunity to amplitude related noise
like that generated by motors,
automobile ignition systems, and lightning. However, World
War II broke out a little over a year later and most commercial
radio advancements were put on hold. This article from a 1940 edition
of National Radio News could not have predicted that, or
the FCC's decision to relocate the FM spectrum to 88-108 MHz
in 1945 in the closing days of WWII. Some speculate that the spectrum
shift was a ploy by RCA chairman
David Sarnoff to undermine the advantage Armstrong had with
his established FM radio production. Nah, it couldn't be so because
government bureaucrats have never done favors for the benefit of
friends/acquaintances for political favor or wealth.
on Commercial Basis
This article was released to National Radio News by the Federal
Communications Commission, Washington, D. C.
modulation as "one of the most significant" contributions to radio
in recent years and declaring that f-m broadcasting on a commercial
basis is desirable in the public interest, the Federal Communications
Commission recently announced the availability of the frequency
band of 42,000 to 50,000 kilocycles for that purpose. This will
provide 40 f-m channels, each 200 kilocycles wide - 35 to regular
high-frequency broadcast stations and 5 to noncommercial educational
"Frequency modulation is highly developed,"
declares the Commission in unanimous report. "It is ready to move
forward on a broad scale and on a full commercial basis. On this
point there is complete agreement among the engineers of both the
manufacturing and the broadcasting industries. A substantial demand
for f-m transmitting stations for full operation exists today. A
comparable public demand for receiving sets is predicted. It can
be expected, therefore, that this advancement in the broadcast an
will create employment for thousands of person in the manufacturing,
installation and maintenance of transmitting and receiving equipment
and the programming of such stations."
At the same time
the Commission points out that there was agreement among witnesses
at its recent hearing that this new service will not supplant the
service of standard broadcast stations generally and that, therefore.
f-m will not make obsolete the receiver now in use. Standard broadcasting
is on an entirely different frequency band from that to be occupied
by frequency modulation. F-m will not interfere with it. Present
standard broadcasting will continue, and certainly for a number
of years will render full service. The extent to which in future
years the listeners will be attracted away from the standard band
cannot be predicted. Testimony at the hearing indicated that manufacturers
will provide receiving sets capable of receiving both services.
The chief claims for f-m are that it gives more fidelity
and less interference than standard broadcast. The principle of
frequency modulation has long been known but it practical use was
not demonstrated until recently.
There was unanimous agreement
at the March hearing that f-m is superior to amplitude modulation
for broadcasting on frequencies above 25,000 kilocycles. The use
of a wide band of frequencies makes possible a reduction of noise
to a greater extent than attained with narrow-band standard broadcast.
There was testimony that a band width of less than 200 kilocycles
can be used for f-m, but this lessens the noise-discriminating quality
which has been established by experimental operation with the wide
channel. Testimony advocating the narrower band width was not supported
by experience in program service. Moreover, the narrower band width
would jeopardize use of facsimile transmission on the same channel.
The Commission believes that regular program service should begin
on a 200-kilocycle band basis which can be conveniently reduced
if developments warrant. By adopting the wide-band f-m channels
at this time, it will be possible for the public to continue the
use of receivers designed for wide-band reception even though narrower
channels may later be authorized.
The opening of a new band
for commercial broadcast will help to correct numerous defects and
inequalities now existing in the standard broadcast system. These
inequalities result from the scarcity of frequencies, their technical
characteristics, and the early growth of broadcasting without technical
regulation. There is today a lack of stations in some communities,
and other communities do not have sufficient choice of program service.
The establishment of the new broadcast band in the higher frequencies
will enable many communities to have their own broadcast stations.
Experimental operations show that f-m stations can operate
on the same channel without objectionable interference with much
less mileage than is possible with standard broadcast stations.
F-m has the ability to exclude all except the strongest signal Also,
f-m stations require much less mileage separation than do standard
broadcast stations. The service range of f-m stations, though limited,
will in many cases be greater than obtained from the primary service
of comparable standard broadcast stations.
of classes of standard broadcast stations in the same area with
different frequencies and different power has resulted in a wide
disparity in the extent of service to the public. The system of
classification now employed for standard broadcast stations will
not be used for f-m stations. The rules and regulations and engineering
standards to be issued for f-m in the near future will enable applications
to be made for facilities to serve a specified area. F-m stations
will be rated on the basis of coverage rather than power. Competitive
stations in the same center of population will be licensed to serve
the same area.
The present situation of certain standard
broadcast stations having large daytime coverage and restricted
nighttime coverage on duplicated channels will be avoided. The coverage
of f-m stations will be substantially the same both day and night.
However, f-m stations do not have the long-distance coverage of
the present high-powered clear-channel standard broadcast stations.
The latter may be required indefinitely, for widespread rural coverage,
But for covering centers of population and trade areas, the new
class of station offers a distinct improvement.
deems it in the public interest to allocate a contiguous band of
frequencies to accommodate both commercial and educational f-m stations.
The band between 42,000 and 50,000 kilocycles is particularly suited
for this service. Under the new allocation, the same number of frequencies
heretofore assigned to non-commercial educational stations has been
retained, the only change being that the position of such stations
has been moved 1,000 kilocycles higher in the spectrum. This arrangement
permits the same receiver to be used for the two services. The three
educational institutions now authorized to use amplitude modulation
in the non-commercial band can continue to do so, but the Commission
hopes that subsequent applicants for non-commercial educational
broadcast facilities will find it economic and otherwise preferable
to utilize f-m.
Frequencies Were Reallocated
Readjustment of the ultra-high
radio frequencies to provide the 40 f-m channels between 40,000
and 50,000 kilocycles, as well as seven channels below 108,000 kilocycles
for television service, is pursuant to allocations contained in
Commission Order No. 67.
The solution to finding space in
the crowded radio spectrum for the needs of these two services was
achieved with the cooperation of the Interdepartment Radio Advisory
Committee in Shifting Government frequencies. This committee, representing
13 Federal agencies, advises the President in allocating radio channels
for Government use.
The arrangement gives private services
priority rights between 60,000 and 66,000 kilocycles and between
118,000 and 119,000 kilocycles in exchange for relinquishment to
the Government of the bands 41,000 to 42,000 kilocycles and 132,000
to 140,000 kilocycles.
In addition, the Commission discontinued
television service in the present television channels Nos. 1 and
8 (44,000-50,000 kilocycles and 156,000-162,000 kilocycles respectively).
Accordingly, old television channel No.2 will be renumbered television
Channel No.1; and a new television channel No.2 will be assigned
from 60,000 to 66,000 kilocycles. Former television channel No.
8 (156,000-162,000 kilocycles), together with frequencies between
116,000 and 119,000 kilocycles, will be used to replace the assignments
in the band 132,000 to 140,000 kilocycles. There is no change in
the other eleven channels comprising the 162,000 to 300,000 television
Unlimited Operation May Be Authorized After January
The new allocations become effective immediately on
a limited basis. After January 1, unlimited operation may be authorized.
Regular commercial service employing wide-band f-m, which may include
the multiplexing of facsimile transmission simultaneously with aural
broadcasting, will use the 43,000 to 50,000 kilocycle band, and
non-commercial educational broadcasting stations are given the new
frequencies 42,100, 42,300, 42,500, 42,700 and 42,900 kilocycles.
This provides a continuous band for f-m, thus assuring a degree
of uniformity in the quality of the different frequency modulation
channels and tending toward simplicity and economy of f-m receiving
The rearrangement permits the Commission to maintain
seven television channels below 108,000 kilocycles and at the same
time provide an adequate number of channels for frequency modulation.
It expects these and other services to benefit by the changes.
It points out that sky wave interference on frequencies
immediately below 50,000 kilocycles is greater than on the higher
frequencies. While it likewise recognizes that shadows and fading
become more pronounced as the frequency increases, it nevertheless
believes that such factors are not substantially different on frequencies
in the vicinity of 60,000 kilocycles. Furthermore, it is generally
conceded that the problem of diathermy interference is now most
acute on frequencies immediately below 50,000 kilocycles.
Thus, by allocating 60,000 to 66,000 kilocycles instead of 44,000
to 50,000 kilocycles to the television service, a good balance has
been achieved between the effects of sky wave and diathermy interference
on the lower frequencies and the effects of shadows and fading on
the higher bands.
The miscellaneous radio services now assigned
frequencies between 132,000 and 140,000 kilocycles will benefit
by the changes in that 9,000 kilocycles are now allocated where
formerly only 8,000 kilocycles were available. This can provide
70 channels as compared with 57 channels in the past. The change
has the further advantage of providing two large blocks of frequencies
for experimentation with different propagation characteristics.