ST-809B New Product Bulletin ST-809B New Product Bulletin

ST-809B Miniature DTMF Decoder

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DESCRIPTIONST-809B Miniature DTMF Decoder

The new Selectone ST-809B is a miniature, universal DTMF decoder module designed for operation over any voice grade circuit such as radio, microwave, or telephone lines. Compatible with the widely used DTMF (Touch-Tone®) signalling format, the ST-809B is typically used for mobile radio paging, selective calling, or remote control applications.

Due to its small size (1.34"L x 0.85"W x 0.21"H), the ST-809B is ideally suited for installation in portable and mobile two way radios. The ST-809B will respond to an address code of 1 to 7 digits in length, using any of the 16 DTMF characters. Because there are no restrictions in the use of repeated digits, this provides more than 250 million unique address codes.



In a typical mobile radio selective calling application, the ST-809B will mute the radio to block out unwanted channel traffic while awaiting a call. When the correct DTMF address code is received, the ST-809B provides a latched output to un-mute the radio, a momentary output to activate a buzzer or vehicle horn, and an additional latched output to activate a "call" lamp or LED. In addition, the ST-809B provides a transpond acknowledgment tone to confirm receipt of the call and an alert tone output for local user alerting applications.

The ST-809B supports individual, group, and "all call" applications for maximum selective calling flexibility. A "radio kill" function is also provided to remotely disable a lost or stolen radio. The status of this function is stored in a non-volatile EEPROM and may be re-set over the air by the servicing dealer or fleet manager.

For remote control applications, the ST-809B provides three separate open collector control outputs which may be toggled on or off individually or interlocked in two different modes. Whenever any remote control output is turned on or off, the ST-809B generates a transpond tone to confirm operation.


Like most Selectone products, the ST-809B is PC programmable using the Selectone ST-809PM Product Manager software. Product Manager is available in both Windows and DOS versions and may be ordered from the factory or downloaded from the Selectone 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


The ST-954 Programming Kit is required for programming the operating parameters of the ST-809B. The ST-954 kit consists of three items: a ST-954B Programming Adapter which interfaces between a PC and the ST-804A encoder; a 6’ RS-232C serial cable assembly; and a DB9 to DB25 adapter plug. The ST-954 kit may be used to program most Selectone products.




Power supply voltage


  25 V dc
Power supply current     7 mAdc
Open collector output (sink current)     80 mAdc
Call Lamp output current (sink or source)     80 mAdc
Temperature range -30   +60 °C
DTMF input (HI range) 30   850 mV RMS
DTMF input (LO range) 10   280 mV RMS
Signal to noise ratio 12     dB SINAD
DTMF twist     ±10 dB
Digit recognition time 20     mS
Interdigit time 50   5000 mS
Decode time* 0   1 Interdigit time
Decode Momentary time 0.050   9999 Sec.
Transpond/Alert tone level     5 V p-p, no load
Transpond duration   2.34   Sec.
Transpond Tone Freq.   874   Hz
Alert Tone Freq.   528   Hz
Call Lamp Flash (50% duty cycle) 100 500 999 mS
Interconnect Type 13 pin miniature low profile connector
Size 1.34"L x 0.85"W x 0.21"H
(34.0mm x 21.6mm x 5.33mm)
*  Measured from the end of the last DTMF character in the sequence

Specifications and descriptions subject to change without notice


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© 1999, Communications Specialists, Inc. All rights reserved.
Revision 6/30/99
Last updated August 06, 1999