CMX138A

– Audio Scrambler

Processors for Two-Way Radios

CMX138A

– Audio Scrambler

The CMX138A is a half-duplex audio scrambler and sub-audio signalling processor for analogue two-way radio applications. This makes it a suitable device for the leisure radio markets (FRS, MURS, PMR446 and GMRS).

This device provides a user programmable frequency inversion audio scrambler with compander and pre/de-emphasis – performing simultaneous processing of sub-audio and in-band signalling.

Other features include: an auxiliary ADC channel and an auxiliary DAC interface (with optional RAMDAC) to facilitate transmitter power ramping.
The device has flexible powersaving modes and is available in a 28-pin (E1) TSSOP package.

This enhanced pin-compatible IC supersedes the CMX138.

Devices are available through our Distributor Network.

Download Datasheet

Block diagram of the CMX138A Audio Scrambler and Sub-Audio Processor showing RF, modulator, discriminator and C-BUS connection to a host microcontroller

CMX138a_block_diagram

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CMX138A FAQ

I have been looking for a CTCSS and Voice band scrambler IC and have found the CMX138A device, which will be ideal for my project.However, I note that it has only one modulator output, this is a shame, as I would prefer to use it with a radio that allows Two Point Modulation.What is the best method of interfacing the CMX138A to such a radio?

A. CML has a number of devices that are available with two modulator outputs, designed specifically for radios that operate two-point modulation, for the CMX7041 – 7041FI-1.x is one such example.

The CMX138A is optimised for low cost radios, which means that some compromises were required, this includes the use of a single modulator output pin. However, it is possible to use the device with such a radio by allowing for a method of external alignment in production.

The hyper-linked (Two-point Modulation Example) illustration demonstrates a simple method of interfacing and comes complete with a suggested method of adjustment. When designing a two-point balancing circuit, such as that shown, it is important to remember the 20k ohm output load limit of the CMX138A.

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FDMA Systems: dPMR Analog PMR
TDMA Systems: DMR
LD or I/Q Interface: I/Q
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Supply Voltage (V): Core 1.3 V IO 2.5 - 3.6 V
Typ. Current (mA): /
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FDMA Systems: PMR446, FRS, MURS, GMRS, Leisure Radio
TDMA Systems: /
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Embedded Functions: Audio Processing, DTMF, CTCSS, DCS, Selcall, Programmable Tones ADC
Supply Voltage (V): 2.7 - 3.6
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Typ. Power Consumption (mW): /
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FDMA Systems: PMR446, FRS, MURS, GMRS, Leisure Radio
TDMA Systems: /
LD or I/Q Interface: LD
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Supply Voltage (V): 2.7 - 3.6
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Typ. Power Consumption (mW): /
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TDMA Systems: /
LD or I/Q Interface: LD
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Typ. Power Consumption (mW): /
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