"Calling all cars, calling all cars, be on the lookout..."

 

This page isn't specific to L.A.P.D., but rather about radios used by the public to listen to police calls across the country.

 
The earliest police radio "systems" were simple arrangements with local AM radio broadcasters; when the police received a call of sufficient importance, they would phone it to the radio station where the announcer or engineer would interrupt the regular program to announce the call...the police cruisers kept their AM car radios tuned to this radio station. Chicago Police, for example, used WGN's (720-AM) facilities for about a year starting in 1929. After about a year they decided this new invention was workable, so they applied to the Federal Radio Commission and got licences for three transmitters around Chicago on 1712 kcs.

Having been able to "eavesdrop" on the police calls for a while, the public had developed an interest in continuing to listen in after the government gave the police some frequencies of their own. Fortunately, several of the early police frequencies were close enough to the "top of the AM dial" to be able to be received on home radios with little or no retuning. And the radio manufacturers weren't far behind, and soon were marketing radios with the police frequency range right on the dial.


Click on the radios below to see how early manufacturers set up their dials for the millions of Americans who've enjoyed listening to their local "police calls" for three quarters of a century.
     

Click on pic to zoom in
Click on pic to zoom in
Click on pic to zoom in

Here's a 1941 Philco 90 receiver, with the "AM Broadcast" band across the bottom of the dial, and "Police - Amateur - Police - High Seas" shortwave frequencies shown across the top.
Not sure of the date or model of this Westinghouse receiver. It appears to be made of "Bakelite," a plastic-like material that was popular in the late 1930s and into the 1950s. At the extreme right end of the dial it says "Police" and "1700" (kilocycles).


This Stewart-Warner Model 9182 was built about 1954...if you click for an enlargement, you can see the triangular "Conelrad" synbols at the 640 and 1240 positions.

     

 

Specially-made "Police" Receivers and Converters

In the American entrepreneurial spirit, a number of companies and individuals got involved in some areas of the new pasttime of listening to the police calls. Radio directories, such as "Radio Craft," and "Callbook" published radio frequencies and callsigns. Some police departments even publicized their frequencies and codes, knowing that the vast majority of listeners were law-abiding and police supporters, and were potential "eyes and ears" for the departments.

By 1938, many agencies had begun using two-way radios in their patrol cars. The station transmitters remained on the AM "medium wave" band, but the cars' transmitters were on much higher frequencies, first in the 33 megacycle range and soon in the 39 mcs band. About 1939, the low-profile but high-production "Detrola Radio and Television Corporation" of Detroit MI introduced their popular...


"Detrola 207 VHF Converter"
Information and photo courtesy of Henry Rogers, Western Historic Radio Museum


The Detrola 207 was an AC-powered radio, which could receive from 25 to about 63 megacycles; its output would then be tuned on an ordinary household radio in the 550 to 700 kcs range, in the lower portion of the standard AM broadcast band. The user would first connect the attached green wire to an antenna of some sort, and the blue and black "twisted pair" to the AM radio...blue to its antenna input, and black to the chassis or ground. To receive the 25-63 kc frequency, the user was instructed to "Set the broadcast receiver to any clear frequency between 550 and 700kHz. Tune the 207 until a station is heard. Tune the 207 for best signal then fine tune the broadcast receiver for best signal."

(40 years later, other types of converters became extremely controversial - and then illegal - because they allowed the user to tune in cellular phone calls on a regular scanner.)


Check back here soon. I'll be adding more information and photos of receivers, scanners, etc...



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