Manual # 600-1501
June 19, 1999
Rev. A - 99038
P R O D U C T G R O U P
OPERATING INSTRUCTIONS
Model ST-25B
Rolling Code Voice Encryption Module
OPERATION
Operation is almost transparent to the user. The user may select any one
of 4 previously programmed User Code Keys. The user then enables or
disables the transmit cipher mode. Once enabled all subsequent
transmissions will be ciphered using the selected User Code Key.
Ciphered reception is automatic; other units transmitting with the
selected code key will be automatically deciphered. Clear transmissions
will also be received automatically.
Each radio model provides different operational challenges. This is
generally due to availability of unassigned switches or blank panel
space capable of supporting accessory switches. To accommodate
these varying situations the ST-25B provides two modes of operation for
enabling and disabling transmit cipher operation, and making User
Code Key selections.
SWITCHED MODE
This is the default mode of operation, as shipped from the factory.
Clear/Ciphered switching is achieved by a dedicated switch
providing a single closure to (-) Supply. User Code Key selection is
also selected by a dedicated switch providing a binary input to the
two Code Select lines on the ST-25B.
DOUBLE CLICK MODE
This mode of operation is enabled during programming. Operation
with this mode minimizes accessory switch requirements on the
radio. The Clear/Ciphered line is connected to any switch (except
PTT) capable of providing momentary closures to or away from
ground. The switch retains its normal functions; however the user
can toggle between Clear/Ciphered by operating the switch two
times in rapid succession (Double Clicking). The ST-25B will then
provide a tone output to the radio speaker. A high frequency beep
or series of beeps indicate subsequent transmissions will be
ciphered. A low frequency tone for .5 Sec. indicates subsequent
transmissions will be in the Clear (NOT Ciphered).
User Code Keys are selected by operating the same switch four
times in rapid succession (Quad Clicking). Quad Clicking permits
switching between User Code Keys when in the transmit Cipher
Mode (Double Click selection). Each Quad Click transaction
advances the selected User Code Key one step around a loop of
possible selections (Primary, Alt #1, Alt #2, Alt #3, Primary ...).
Following a Quad Click sequence the ST-25B responds with
speaker beeps to indicate the selection position (Primary: 1 Beep,
First Alt: 2 Beeps, Second Alt: 3 Beeps, Third Alt: 4 beeps). When
returning to cipher mode from clear mode, the last used User Code
Key will be selected and indicated with speaker beeps. Following
power-up Cipher operation will select the Primary User Code Key.
Slow switching of this control permits operation in a normal manner
as assigned by the radio manufacturer. Typically this is connected
to the monitor switch, but other switches can be used (freq.
select).
In either mode a visual cipher indicator is available.
INITIAL SYNCHRONIZATION DELAY
All radio systems have an operating delay. This is the time between
PTT activation at a transmitter and speaker audio being available at
the receiving point. This time may vary considerably from system to
system or even from transmission to transmission. For reliable cipher
operation, the ST-25B must wait for this time period before signaling
the beginning of a ciphered transmission. System delays must be
evaluated and accommodated for with the INITIAL SYNCHRONIZA-
TION DELAY parameter.
GENERAL
The ST-25B is a frequency domain rolling code voice encryption device
used to protect the security of two way radio communication systems.
The cipher process uses a proprietary microprocessor controlled analog
scrambling algorithm. Each unit can be programmed with four User
Code Keys, with over 4 billion code keys to choose from. Special
factory set master code key groups are reserved to provide extra security
for special services. Each master code key group has over 268 million
possible code keys. To maintain security, code keys are never
transmitted. Audio processing filters provide high quality low distortion
recovered audio. The small size and low power requirements make it
ideal for portable, mobile, and base station use.
The ST-25C and ST-25B are code-compatible and may be used in the
same system. The only difference between the two units is that the
ST-25C provides a path for CTCSS tones while the ST-25B does not. The
ST-25B should be used when the unit is installed in the receive audio
path after the CTCSS decoder. The ST-25C must be used if the unit is
installed before the CTCSS decoder.
Field programming is accomplished using a PC serial connection, and
Product Manager Software. Product Manager is available on disk from
SmarTrunk at a nominal price, or it is available at no charge on the
Selectone web page
www.selectone.com.
Product Manager is supplied
as two separate programs for use with Microsoft Windows or DOS.
ST-25PM
Windows & DOS based Product Manager
ST-954B
RS-232 to Selectone connector adaptor.
Application information is available or can be developed for most radio
models. Documentation on ALL current products and many of our
application notes are available for instant access on our web site
www.selectone.com.
If you would like application details for a specific
radio, please call us at (510)887-1950 or request assistance via E-Mail
OPERATING SPECIFICATIONS
SPECIFICATION
DETAIL
Encryption: .......................................
32 bit algorithm
Operating Voltage: ..........................
5.2 Vdc to 16.3 Vdc
Operating Current: ..........................
< 8mAdc
User Code Keys: ..............................
Greater Than 4 billion
Cipher Algorithm: .............................
Real Time Frequency Domain
Synchronization: ..............................
Initial and Maintenance
Usable Audio Level Rx and Tx: ..........
25 mV p-p to 2.0 V p-p
Input to Output Gain: ......................
< ± 1 dB
Frequency Response: ......................
300 Hz to 2600 Hz
Temperature Range: ........................
-30
°
C to +60
°
C
Interface: .........................................
18 flying leads terminated in a
13 pin low profile connector
Size: ..................................................
0.90 W x 1.50 L x 0.18 H
(22.8mm x 38.1mm x 4.6mm)
IMPORTANT
Note:
Operation of radio equipment with encrypted speech capability
may be government regulated. The purchaser of this equipment is
responsible for compliance with applicable radio regulations regarding
operation of this equipment.
Note:
Export of this product is under the jurisdiction of the U.S. Depart-
ment of Commerce, Office of Defense Trade Control.
An Export
License is Required.
