Q. I have been looking for a CTCSS and Voice band scrambler IC and found the CMX138 device which will be ideal for my project. However, I note that it has only one modulator output. It's pity that I would prefer to use it with a radio that allows Two Point Modulation. What is the best method of interfacing the CMX138 to such a radio?
A. CML has a number of devices that are available with two modulator outputs. In CML website (Two-point Modulation Example), it 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 CMX138.
FX469 & CMX469A
Q. What is the difference between the FX469 and the CMX469A?
A. There are no major differences between the FX469 and the CMX469A. The CMX469A is the preferred device for new designs and it possesses the advantage of operation down to 2.7V DC. For those customers contemplating migration to the CMX469A, there is a difference in the operation of the Carrier Detect Output that may be important. When power saved the FX469 Carrier Detect always returns to Vss (low).
The CMX469A however, always maintains its last state. Thus, a CMX469A that is power saved while receiving FSK data will maintain its Carrier Detect high.
Current consumption is the same, 4.5mA at 5V, but this can be further reduced at 3V to 2mA, giving significantly reduced power consumption. The CMX469A is also available in a smaller package: A TSSOP for space constrained designs.
Q. I am interested in establishing a voice link between a CMX639 and CMX649. How do I configure the CMX649 for this application?
A. While the CMX649 can perform CVSD voice coding through its first order integration, the CMX649 is not signal compatible with the CMX639, and hybrid systems using both devices should not be attempted.
Q. Can I connect the CMX7011 Digital Scrambler directly into a radio's audio
A. Yes. That is the intended use of the CMX7011; however there are a number of considerations that need to be taken into account. To achieve optimum performance, radio specific interface circuitry may be required.
When the radio is in digital voice scrambler mode, the radio's audio path: 'pre/de-emphasis', 'companding', ‘VOX� and any audio band filtering, should be turned off.
CMX7032, CMX7042, CMX7045
Q. I find a new product CMX7045 on your website, what are the differences among CMX7045, CMX7032 and CMX7042?
A. the CMX7045 is a highly-integrated and flexible baseband processor, fulfilling the needs of an AIS-SART, meeting IEC 61097-14 requirements and targeting marine AIS-SART applications. In addition to providing the core AIS-SART formatted data functionality, the CMX7045 incorporates a number of auxiliary operations that assist in the overall system implementation thereby reducing overall component count and cost. That means it is cheaper than CMX7032 and CMX7042. In addition, they have different applications. CMX7032 is designed for Class A and CMX7042 is Class B.
Q. I need a chip which is used in DMR. Which one you would like to recommend?
A. CMX7861 meets your need. It is a full-featured analogue front end for DSP/Microcontroller based systems. It aims at DMR, PDT, APCO P25 Professional digital trunking communication and wireless transmission terminal. It has the following features: the input/output interface of CMX7861 is flexible configuration, tradition analog and I/Q-based operation is supported. 2. It can be compatible with CMX99x RF devices of CML.
CMX881, CMX882, CMX883
Q. I am starting out my design with a CMX88x device, are there any suggestions in how best to handle interrupts and Status Register flags?
A. The CMX88x series of devices are complete and functionally dense devices, to allow this many functions the Status register must be checked at an appropriate time by the users� code.
In most CML devices both polling of the Status Register and a full interrupt driven scheme are suitable; however due to the added complexity within the CMX88x, polling of the Status Register, without first ensuring that an IRQN has been generated, must not be performed.
Q. I have a number of CMX910 samples that have been supplied to me. Can you explain what the 'ENG' marking means at the start of their product code?
A. When supplying a latest product, CML often supplies devices as 'engineering samples', any device with markings that resemble ENG099xxx will be an engineering product.
CMX910 engineering devices have been shipped with the following batch codes, ENG099340, ENG099342, ENG099356, ENG099392 or ENG099393.
Q. I see that I and Q methods of generating and receiving baseband signals for wireless data devices is popular with CML, can you direct me to sources of I/Q hardware; for example I/Q mixers?
A. CML has a range of devices supporting I/Q architectures including the CMX991 (I/Q transceiver), CMX992 (I/Q receiver), CMX993 (I/Q modulator) and CMX998 (Cartesian Loop modulator).
Q. Can the CMX998 be used for TETRA 2?
A. Yes, the CMX998 meets the linearity and wideband noise requirements of TETRA QAM modes for 25 kHz, 50 kHz, 100 kHz and 150 kHz channels.
Note that a different loop-filter might be required for the 100 kHz and 150 kHz channels.
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