Mobilecall Voice Encryption Modules Model ST-25AMC and ST-25AMT PDF Installation Instructions User Guide

The ST-25AMC and ST-25AMT are voice encryption devices for use with the Motorola MC-2100 & MT-2100 Transceivers respectively. The cipher process uses a proprietary microprocessor controlled digital scrambling algorithm. Each unit can be programmed with up to four User Code Keys, with over 4 billion code keys to choose from for each User Code Key. 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. NOTE: Though the ST-25AMT can accept four user code keys, the application characteristics of the MT-2100 radio limits the accessibility to only one User Code Key.

SPECIFICATIONS
Total Code keys: Over 4 billion
Operating Voltage: 5.2 to 18Vdc
Operating Current: < 8mA
User Code keys: Over 268 million
Ciphered Algorithm: Real time frequency domain
Synchronization: Initial and maintenance bursts
Delay Before Initial Synchronization: Programmable 50mS to 1.2S
Input to Output Gain: Less Than ± 0.5 dB
Frequency Response: 300 Hz to 2600 Hz.
Programming: External Keypad (ST-905 V1.3 or greater) PC Programmer (ST-907 VER 3.2 or greater)
Memory: Non-volatile EEPROM
Indicators: Audible (Spkr. Beep)
Digital Inputs: Logic Low, less than 1 Vdc Logic High, Greater than 4 Vdc
Temp. Range: 30°C to +70°C
Interface: Flying leads terminated at a low profile connector
Size: Customized to permit installation in the MT-2100 transceiver.

The ST-25AMC and ST-25AMT circuit boards are identical. The only differences are the application details and programming to accommodate the specific application. Operation is almost transparent to the user. The user has the capability to enable or disable the transmit cipher mode. Once enabled all subsequent transmissions will be ciphered using the selected code key (User Code Key selection is not available with the ST-25AMT). Ciphered reception is automatic; other units transmitting with the selected code key will be automatically deciphered. Clear transmissions will also be received automatically.

Normal Non-Encrypted Voice Operation
Upon power-up MC-2100 operation is not noticeably different than operation prior to installation of the ST-25AMC. All normal MC-2100 functions and operational capabilities are unchanged. If the radio receives a clear, non-ciphered signal the clear audio will be heard on the speaker. If the radio operator presses the PTT button and speaks into the microphone transmissions will be “in the clear” (non-ciphered). Encrypted Voice Reception If a synchronization signal from another correctly coded Selectone ST-25 series Encrypted Voice device is received, the ST-25AMC will automatically switch to de-cipher mode. De-ciphered audio will be heard on the speaker. If a synchronization signal from an incorrectly coded Selectone ST-25 series Encrypted Voice device is received, unintelligible ciphered audio will be heard on the speaker.

Encrypted Voice Transmissions
To produce ciphered transmissions the ST-25AMC must be placed in the ciphered transmission mode. This is accomplished by special operation of the monitor switch on the radio. This switch is the lower left most switch on the radio front panel. The monitor switch provides a dual function. First it operates normally for radio functions. Secondly the user can toggle between Clear/Ciphered transmissions by operating the switch two times in rapid succession (Double Clicking). The ST-25AMC will then provide a tone output to the radio speaker. A high frequency beep indicates subsequent transmissions will be Ciphered. A low frequency tone for .5 Sec. indicates subsequent transmissions will be “in the clear” non-ciphered. Normally following power-up, operation will be in the clear mode. The user must take the above described action to select the ciphered transmission mode.

User Code Key Switching
The double click mode described above also provides access to User Code Key selection. To select an Alternate Code Key, operate the monitor switch four times in rapid succession (Quad Clicking). Each Quad Click sequence advances the selected User Code Key one step around a loop of four possible selections (Primary, First Alternate, Second Alternate, Third Alternate, Primary…). Following a Quad Click sequence the ST-25AMC responds with speaker beeps to indicate the selection position. Primary 1 beep; First Alternate 2 beeps; Second Alternate 3 beeps; Third Alternate 4 beeps.

When returning to ciphered transmission mode from clear transmission mode, the last used User Code Key will be retained and indicated with speaker beeps. User Code Key selection is initialized at the Primary User Code Key on power-up.

Download Mobilecall Voice Encryption Modules Model ST-25AMC and ST-25AMT PDF Installation Instructions User Guide


March 13, 2010 | Posted in Audio Video Manual, Electronic Manual

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