Split-band scrambler for private communications

28 February 2001 Telecoms, Datacoms, Wireless, IoT

CML is offering a simple-to-use dual mode voice-band scrambler that it claims is low cost and that will keep your conversations private. The company's CMX264 frequency domain scrambler uses split-band frequency inversion scrambling which provides a superior level of speech privacy than single inversion methods often employed by other solutions. To further enhance security the device has easy-to-implement fixed and rolling code capabilities. All the filtering required is also featured on-chip.

Typical current requirement is 3 mA at 3,0 V making the CMX264 an ideal solution for any audio application where low power consumption is critical. These include mobile radio and FRS/PMR446 handsets, both wireline and mobile telephones, fixed or rolling code voice scramblers and baby alarms. Energy efficiency is increased by the devices' standby mode.

The CMX264 operates using a simple serial interface or microprocessor control. For full duplex operation Tx and Rx audio paths are separate. In the Tx path, scrambling is achieved by splitting the audio into two parts and frequency inverting each one. The frequency at which the signal is split, the 'split-point', can be either fixed or rolling between four possible settings. This results in a transmitted audio which is unintelligible to eavesdroppers.

Descrambling is achieved by a receive device set to the same split-point as the remote transmitter. Thus if the Tx and Rx devices are synchronously cycled through the same sequence of split points, a clear recovered signal will emerge at the output of the receiver. The use of a 4,433619 MHz crystal allows up to four split points to be programmed. It comes in a in 24-pin SSOP package.

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