In one of my previous careers I served for over 12 years as a 911 dispatcher in
two states. My first dispatch job was in Rockford IL in the late 70s where I
fondly remember the long wire antenna running between the old police
headquarters roof and the roof of city hall at the opposite corner of the
block. I was told that this was the antenna used for the old AM transmitter
which had been located on the roof of the police station. The antenna wire was
a heavy looking mutli-strand cable and the insulators at each end looked to be
about 2 feet in length. The Rockford police went on the air in 1933 and
converted to two-way radio in 1940. Several years ago I researched some of the
history of police operations in the AM band. The Galvin Manufacturing Company
of Chicago (Motorola was their brand name) realized that many police
departments were ordering car radios from them for use in their police cars.
Recognizing a market for a police specific product in 1936 they introduced a
spe!
cial receiver called the Motorola Police Cruiser. It was capable of receiving
from 1550 kc to 2800 kc. One of the primary differences from the Motorola car
radio was that the police receiver was crystal controlled for frequency
stability on a specific channel. At this time Galvin was having trouble meeting
the demand for its very popular Motorola car radios. So initially the police
receivers were only produced on weekends so as not to disrupt normal car radio
production during the week. By 1936 Galvin had introduced an AM mobile
transmitter operating in the 30-40 mc "UHF" band to enable police cars to talk
back to the dispatcher via radio. In the 1920s and 1930s many police
departments in the US broadcast on 1712 or 1714 kc. There are reports that at
night these channels were so busy that the various police departments across
the country had to take turns broadcasting. Some of the early police
transmitters sent Morse code messages instructing individual squad cars to
respon!
d to a call box to get their message via telephone. As early as 1921 t
he Detroit police had a mobile radio system. The transmitter had the call sign
KOP which some attribute to the origin of the word "cop" as a slang for police
officers (most likely "cop" is a shortened version of "copper" resulting from
the common use of copper badges many years before the Detroit radio system
existed). The Detroit system operated on 1050 kc and later was moved to 1080
kc. Some exceptions to the 1712/1714 kc frequencies that I noted were Berkeley
CA on 2410 kc, and most radio equipped departments in the state of Tennessee on
1619 kc. A history of the Denver police radio system indicates that they
operated on 1610 kc. That history mentioned that this was a common nationwide
police frequency as well and mentions Denver police cars relaying messages at
night between various western US police agencies. Relays between Indio CA and
Kansas are specifically mentioned. It also mentions that the Grand Junction CO
police were on this frequency as well and came in so cle!
ar that Denver officers sometimes responded to calls with similar addresses
that were actually intended for Grand Junction officers. I found a reference
stating that in 1949 the FRC (pre-FCC) ordered all law enforcement stations to
move to VHF. However, it appears that it may have taken years for this move to
be completed. Here are some early police radio call signs taken from various
historical references: KOP Detroit, KGPX Denver, WPGD Rockford IL, WLAW New
York City, WMAZ Indianapolis, KSW Berkeley, WPDA Tulare, KGJX Pasadena, KGPL
Los Angeles, KGPI Omaha, KGZY San Bernadino, KGPC St Louis, WPDB WPDC WPDD
Chicago, WRR Dallas.
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