Pocket sized transmitter, frequency modulated by crystal derived tones, with integral loop antenna provides police with easy operating alert signal communicator which uses patrol car radio to relay signal. Communication channels are time shared by several patrol units

Baker, C. D.

Couvillon, L. A.

Hubbard, W. P.

Kollar, F. J.

Postal, R. B.

Tegnelia, C. R.

English

NASA Technical Reports Server

August 1971
	 Brief 71-10307 
NASA TECH BRIEF
	
41 
NASA Pasadena Office 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Tone-Activated, Remote, Alert Communication System 
The problem: 
To provide a police officer with an easy-to-operate 
alert signal communicator which uses the patrol car 
radio to relay the signal. 
The solution: 
A pocket sized transmitter, frequency modulated 
by crystal-derived tones, with an integral loop anten-
na. The tone modulated FM is transmitted to a 
narrow band receiver/detector and tape player 
mounted in the patrol car, and either one of two 
pre-recorded alert messages is transmitted over the 
patrol car transmitter to the central dispatcher. 
Because the allotted time for the recorded message 
and the patrol unit location information is relatively 
small, the communications channel can be time-
shared by several patrol units. In addition, the 
signals and the detector have a very narrow band-
width (1 Hz), providing an additional advantage over 
the voice channel. 
How it's done: 
Initially, the design requirement was for a reliable 
one-way communications link from a police officer 
away from his car to the dispatcher. 
The specific design implemented includes a red 
alert signal, transmitted when the red alert push-
button on the transmitter is activated. The signal 
consists of a 100 Hz tone which modulates the 
FM transmitter. The transmitter in turn radiates 
the signal, via the closed-loop antenna and through 
the RF transparent wall of the transmitter case, to 
the patrol car mounted receiver/tape player and 
control unit. The receiver output is applied to a
narrow-band detector consisting of a bandpass 
filter, and driver and vibrating reed relay stages. 
The narrow-band characteristics of the reed re-
lays used as filters, and the low-pass filters following 
the relays, result in a significant performance im-
provement over the voice channel. This performance 
advantage makes up for losses due to the inefficient 
small antenna and propagation losses through the 
building walls (should the policemen be inside a struc-
ture). 
The 100 Hz signal is passed through binary logic 
gates in order to (1) select the tape track on which 
the red alert message is recorded, and (2) turn on 
the tape player. The recorded message triggers the 
voice detector circuit to turn on the patrol car 
radio transmitter, and the red alert message, pre-
recorded on tape together with the identity of the 
patrol unit, is broadcast to the dispatcher. 
The second signal available in the original design 
is the yellow alert message, consisting of a 400 Hz 
tone, which performs the same functions as the red 
alert message tone, but on a second tape track. 
Power for the remote unit is provided by a 9 V 
battery contained in the case. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B71-10307
(continued overkal) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19710000305 2020-03-17T02:21:41+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: L. A. Couvillon, R. B. Postal, 
F. J. Kollar, W. P. Hubbard,
C. R. Tegnelia, and C. D. Baker of
Caltech/JPL
under contract to
NASA Pasadena Office
(NPO-1 1132) 
Brief 71-10307'	 Category 02


Tone-activated, remote, alert communication system

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