Реферат: FM Broadcast Radio On The Old 45MHz
FM Broadcast Radio On The Old 45MHz Band Essay, Research Paper
The old 45MHz FM broadcast band
In 1945 the FCC decided that
FM would have to move from the established
42 – 49 megahertz pre-war band to a new band at 88 – 108 megahertz,
to make way for television.
Both in frequency spectra and
consumer dollars. Therefore, all radios with an FM band
of 88 to 108MHz are post-war.
RCA’s David Sarnoff in particular wanted FM to
“go away” so the public wouldn’t be distracted from
buying his latest up and coming product: televisions. Maybe if
Armstrong said to Sarnoff in the early days
that FM sound would be perfect for the television
soundtrack, they wouldn’t have become rivals.
Turns out modern TV doesn’t even use this spectra.
There was to be a channel 1 here. But co-channel interference
from stations in distant towns would occasionally happen. And
this would be worse for television than FM signals, as FM has
the FM capture ratio working in its favor. FM receivers
will capture a signal that is a few dB stronger than another
co-channel signal, without the weaker signal causing interference.
TV, being an AM type signal with one sideband partially suppressed,
would suffer more severe interference for the same given
signal strengths. Seems odd that the FCC
chose to replace FM with TV in this spectra, but they were more
politically motivated by RCA than scientifically.
Channel 1 was to be used by low power TV stations, and police and fire
users in areas without a channel 1 TV station. Interference to
a TV channel from a fire or police station would be particularly
objectionable when propagation was good.
TV channel 1 was dropped, and land-mobile fire and police now
use this spectra everywhere. These users would sometimes hear distant signals,
as the local signals are usually off.
They do not broadcast continuously like commercial stations.
FM Capture ratio doesn’t help you ignore weaker
signals if your local station isn’t
transmitting. Capture ratio is a feature of FM reception where
the stronger of two FM signals will dominate. The weaker signal
will not be heard at all. Fire and police departments in different
jurisdictions use differing audio tones
to help discriminate between each other. Some older
cordless phones can be heard on these frequencies. Commercial broadcast
would have been a better use of this band.
Because of this reallocation, more than half a million FM
some 50 transmitting stations would be
rendered obsolete. One individual consumer once had a 45MHz
FM tuner, a Meissner 9-1047A,
that was also rendered obsolete. It tuned from 41.2 to 50.4MHz. He didn’t
receive any compensation or trade-in offers for his now useless radio he spent
his own money to purchase.
The Yankee Network of 45MHz stations in
New England did not survive the change.
But the worse fear for Edwin Armstrong (inventor of FM) would be a loss
of confidence in FM by the
growing number of faithful hi-fi listeners.
This move to higher frequencies, however, proved to be
only a temporary setback for FM. By 1950 there were over
600 FM stations on the air in the new band.
GE, Westinghouse, Temple and Stromberg Carlson, to
name a few paid patent
royalties to Edwin Armstrong for FM, but RCA wouldn’t.
Armstrong instituted a suit against RCA and NBC charging them with
infringing his five basic FM patents. RCA’s David
Sarnoff figured he could outlast Edwin Armstrong in court in patent
infringement lawsuits. Sarnoff wasn’t thrilled with FM
being selected by the FCC to carry sound for TV. RCA did outlast Armstrong, who went
Philcos with AM, SW, and the old prewar FM band,
marked with FM channel numbers 21 to 99 were made.
A Pilot AM/FM set with the old FM band was made. Note that the
FM band on this set is the old 45MHz band, and that the normal
AM band is also present. Possibly one of the first AM/FM
sets ever produced.
One may see FM radios with band markings from 201 to 300. These
aren’t MHz markings, but FCC channel numbers for the modern 100MHz
FM broadcast band. Channel 201 is 88.1MHz, 202 is 88.3MHz,
259 is 99.7MHz, etc.
Pre-war FM sets may be marked with numbers
like 21 to 99. These are channel numbers for the old 45MHz
A partial listing of non-experimental stations on the old 45MHz
FM band. In rough order by state:
K45LA Don Lee Broadcasting System, Los Angeles 44.5
K49LA Hughes Tool Co, Los Angeles, 44.9
KALW Board of Education, San Francisco United School District San Francisco, 42.1
WTIC-FM Travelers B/c Service Corp. (WTIC), (45.3), Hartford W53H
WDRC-FM WDRC Inc. (WDRC), (46.5), Hartford W65H
WINX-FM WINX B/c Co. (WINX), (43.2), Washington DC
WTOP-FM/WHUR Jansky & Bailey, Washington DC 43.2
WOWO-FM Westinghouse Radio Stations (WOWO), (44.9 mc), Ft. Wayne
WABW Associated Broadcasters (WBBW), (47.3 mc), Indianapolis
W45V Evansville On the Air, Inc, Evansville IN, 44.5
W79C Oak Park Realty & Amusement, Chicago 47.9
WBEZ Board of Education, City of Chicago, Chicago, IL 42.5
WWZR/WEFM/WUSN Zenith Chicago W51C 45.1
WIUC University of Illinois, Urbana, IL 42.9
WBKY University of Kentucky, Lexington, KY, 42.9
WBZ-FM Westinghouse Radio Stations (WBZ), (46.7 mc), Boston W67B
WMNE Yankee Network (43.9 mc), Boston
WGTR Yankee Network (WNAC), (44.3 mc), Boston W43B
WMTW-FM Yankee Network, Boston W39B
WBZA-FM Westinghouse Radio Stations (WBZA), (48.1 mc), Springfield
WENA Evening News Assn. (WWJ), (44.5 mc), Detroit
W77XL WJIM Inc, Lansing, 47.7
W81SP Westinghouse Radio Stations, Inc, Springfield MO, 48.1
KMBC-FM Midland B/c Co. (KMBC), (46.5 mc), Kansas City
WFMN Edwin H. Armstrong (44.1 mc), Alpine, NJ
WNBF-FM Wylie B. Jones Adv. Agency (WNBF), (44.9 mc), Binghamton
WQXQ Interstate B/c Co. (WQXR), (45.9 mc), New York
WABF Metropolitan Television Inc. (47.5 mc), New York
WEAF-FM/WNBC-FM National Broadcasting Co, New York 42.6
WABC W67NY Columbia Broadcasting System Inc, NY, 46.7
W99NY Frequency Broadcasting Corp, NY, 49.9
WHNF W63NY Marcus Loew Booking Agency, NY, 46.3
W55NY William G. H. Finch, NY, 45.5
WNYC-FM City of New York, Municipal Broadcasting Co, 43.9
WOR-FM Bamberger Broadcasting Service, New York 43.4, 47.1
WGYN W47NY Muzak Corp, New York, 44.7
WHFM Stromberg-Carlson Co. (WHAM), (45.1 mc), Rochester W51R
WHEF WHEC Inc. (WHEC), (44.7 mc), Rochester W43R
WTAG-FM Telegram Publishing Co, Worcester ???
WGFM General Electric Co. (WGY), (48.5 mc), Schenectady
WBCA Capitol B/c Co. (44.7 mc), Schenectady
WMIT Gordon Gray (WSJS), (44.1 mc), Winston-Salem, NC
WELD RadiOhio Inc. (WBNS), (44.5 mc), Columbus W45CM
WBOE Cleveland City Board of Education, Cleveland, OH 42.5
KYW-FM Westinghouse Radio Stations (KYW), (45.7 mc), Philadelphia
KDKA-FM Westinghouse Radio Stations (KDKA), (47.5 mc), Pittsburgh
W81PH Seaboard Radio Broadcasting Corp, Philadelphia 48.1
WSM-FM National Life & Accident Insurance Co. Nasvhille 44.7
K47SL Radio Service Corp. of Utah, Salt Lake City 44.7
WTMJ-FM Journal Co. (WTMJ), (45.5 mc), Milwaukee W55M
WEBC-FM Head of the Lakes Broadcasting Co, Superior, Wi 43
Source, and more info on early FM is at:
Broadcasting History Pages
One can use an old mechanically tuned UHF tuner from an
old TV set to act as a downconverter of UHF TV channel sound
carriers to feed into a set with the 45MHz FM band. Connect
a UHF antenna to the tuner input, and a coax cable to the
(usually) RCA jack that is the IF output. And a power supply
to run the tuner. Tune the radio to about 43MHz, and tune
around on the UHF tuner and you should be able to hear the soundtrack of
UHF TV stations of your area on the radio. Also cell phones
around channel 80, but don’t listen to them!
Japan has their FM broadcast band
between 76 and 92MHz. And television channels occupy the rest
of what would be the American FM band.
The Russian FM band goes from 66 to 73MHz.