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These products are no longer in production. This
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These products are no longer in production. This
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CTCSS (Continuous Tone Coded Squelch System) is the most widely used signalling method for two way radio selective calling applications. Also known as PL (Private Line®) or sub-audible tone, CTCSS is most commonly used to mute the receiver of a mobile radio or base station until an assigned tone code is received, thereby eliminating annoying chatter from co-channel users. CTCSS may also be used to control access to shared repeaters or to selectively call individual radios or groups of radios in a fleet application.
The ST-133 CTCSS Encoder and the ST-139 CTCSS Encoder/Decoder represent the latest technology from Selectone, a leading manufacturer of CTCSS signalling devices since 1979. These new modules are among the smallest in the industry for easy installation and mounting in most portable and mobile radios. Featuring surface mount construction and digital programming, the Selectone CTCSS modules are backed by a full two year warranty and a library of Application Notes for hundreds of different two way radio models.
- Micro Miniature Size — for easy mounting in most portable and mobile radios.
- Digitally Programmable — with solder pad jumpers to any EIA CTCSS code.
- Universal Design — for easy interface to most radio squelch circuits.
- Color Coded Cable Assembly — with low profile connector for easy installation and removal (ST-139 only).
- Fully Compatible With All CTCSS Systems — including Motorola "Private Line", GE/Ericsson "Channel Guard", and E.F. Johnson "Call Guard".
- Full Applications Support — from the leader in CTCSS signalling for over 20 years.
The use of CTCSS allows mobile radio users to block out unwanted traffic on the same radio channel, either from a different user group on a shared repeater system, or from a foreign repeater or mobile. In crowded RF environments, the use of CTCSS is essential to protect against unwanted interference.
When equipped with a CTCSS decoder, a radio receiver will remain muted in the presence of carrier unless the carrier contains the proper CTCSS code. This will effectively block out unwanted transmissions from other radios or repeaters on the same channel. When the correct tone code is received, the radio will unmute for the duration of the transmission. Because the tone is continuous, CTCSS provides positive control of the radio’s squelch circuit during each transmission. Because the tone is sub-audible (below 250 Hz), it is filtered out of the radio’s audio path and does not interfere with normal voice communication.
While most CTCSS applications require an encoder/decoder combination for both transmit and receive, some applications require only an encoder. For example, in some fleet applications, only the base station may be protected with a decoder, in which case the mobile units require only an encoder to unmute the base station.
® Private Line is a registered trademark of Motorola Inc.
The ST-133 CTCSS Encoder and the ST-139 CTCSS Encoder/Decoder are shipped with an instruction manual and double-sided pressure sensitive tape for easy mounting on any flat surface inside the radio package. Instruction manuals for both products may be obtained from our sales department or downloaded from our Website by clicking here.
Application Notes with detailed installation instructions for a wide variety of mobile radios are available free of charge by clicking here. For further applications assistance, contact the Selectone Technical Support Department at (714) 998-3021, or by e-mail at sales@com-spec.com.
The Selectone Product Group also includes DTMF decoders and ANI systems, Two-Tone Sequential and Burst Tone encoders and decoders, and the Selectone Private Collection™ of Voice Encryption Modules for secure speech applications. For more information, please call our sales department at (714) 998-3021.
OPERATING SPECIFICATIONS SPECIFICATION ST-139 ENCODER/DECODER ST-133
ENCODEROperating Voltage
5.5 Vdc to 24 Vdc 5.5 to 16 Vdc Operating Current Less than 5mAdc Less than 3mAdc Frequency Range 67.0 to 254.1 Hz 67.0 to 250.3 Hz Number of CTCSS Codes 47 (Expanded EIA) 40 Temperature Range -30°C to +60°C -30°C to +60°C Frequency Stability Exceeds EIA specifications Exceeds EIA specifications Encode Distortion Less than 2% THD Less than 5% THD Encoder Output Level Adjustable 0 to 1 Vrms Adjustable 0 to 1 Vrms Decoder Input Level 30m Vrms to 1 Vrms n/a Decoder Input Z Greater than 50k n/a Hi-Pass Filter May be muted by decode output Decoder Activate Field selectable (+) or (-) logic n/a Decoder Output Open collector sink to (-) supply or souce (+) Voltage. Four possible output conditions or Hi-Pass filter muting. n/a Interface 18" color coded flying leads with low profile connector 9" flying leads Size
1.6"L x 0.85"W x 0.14"H
(40.64mm x 21.6mm x 3.56mm)0.75"L x 0.45"W x 0.18"H
(19.05mm x 11.43mm x 4.57mm)Specifications and descriptions subject to change without notice
© 1999, Communications Specialists, Inc. All rights reserved.
Revision 5/17/99
Last updated August 06, 1999