Low Cost Data Modems

A guide to the TDL2A family, including RXL2, TXL2 and TDH2
(and the add-on modem chips: i1200, i9600 and the M48)

INEXPENSIVE, EASY TO USE “TRANSPARENT DATA LINK” MODEM MODULES

While the flexibility of a raw baseband interface radio is invaluable, there are occasions where a much simpler-to-use “serial cable replacement” is a better choice. These modules fulfil that requirement.

The idea behind these products is to insulate the user from having to deal with the problematic (noisy, AC coupled) baseband radio path, and all the data processing and burst timing issues associated with driving the wireless modules, and instead present a simple, well behaved “looks like an RS232 link” half duplex serial port, while on the hardware side implementing a superior performance (but still low cost) multichannel wideband radio

For use in the 433MHz band there is a choice of the bidirectional TDL2A and TDH2 (higher power, outside Europe) in the 33x23mm footprint, or the RXL2 (receive) and TXL2 (transmit) pair in more compact SIL packages.

Key features (TDL2A family)

Easily understood 9600 baud serial “data link” operation
Best-in-class RF performance. Superior sensitivity and large signal rejection, compared to typical wideband modules
Compatible with Radiometrix 33x23mm BiM and SIL footprints (TDL/TDH and RXL/TXL respectively)
Multichannel (5 spot frequencies) operation in 433MHz band
Functionally equivalent 869 or 915MHz versions (using the TDL3F board and BiM3x radio)
Higher power (25mW) TDH2 module, for Australian/NZ regulations
Conform to EN 300 220-3 (category two) and EN 301 489-3
Evaluation boards available

Data links

The core of this family consists of the TDL2A and TDH2 transparent data transceivers, and the compatible RXL2 data receiver and TXL2 data transmitter.
  
    Common family features:

  • Fully transparent RS232 compatible data interface (data can be streamed at 9600 baud without buffering)
  • Self timed (No additional user “TXE” signal needed)
  • Full framing / packet detection. No random spurious “line noise” data in absence of a signal
  • Efficient low latency short (3 byte payload) packets. Ideal for control applications.
  • User programmable 1 of 8 address.
  • Simple user control, via human readable command strings over the serial port
  • 10mW (TDL2A & TXL2) or 25mW (TDH2) transmit power output
  • Low power +5v supply (TDL2A: 28mA TX  22mA RX)
  • (RXL2A only) Analogue RSSI output pin 

 

    Higher frequency operation is covered by the TDL3F, which combines TDL type modem hardware (and pin-out) with a BiM3(x) transceiver to cover 869 and 915MHz bands. The DWA3 is (in simple terms) a TDL3F fitted with an integral ceramic antenna


APPLICATIONS

This series of radios are suited to short time-to-market, data intensive commercial applications such as EPOS and meter reading systems, data loggers and vehicle telematic download systems, robotics, and in-building monitoring.
Their simplicity of use also makes them suitable for early stage prototyping of more complex systems, and to add radio data connectivity to “maker” projects

CASE STUDY
TXL2/RXL2
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Beyond the basic family

While the basic TDL2A (and family) provides a very easy to use data link solution, the basic concept (providing extra processing of the data-stream between the user and the radio) can be taken much further. To this end Radiometrix provides a range of easy-to-use “external processor” modem devices. These 18 pin chips require just a power supply and a clock crystal to add the easy to use “serial port interface” of the TDL2A to almost any radio module:

> The i9600 chip allows the 9600 baud serial port interface and radio baseband path data coding of the TDL2A to be added to any (wideband, to accommodate the 16kbit/sec bitstream) wireless module.

> The i1200 chip provides the exact same functionality (at the lower data rate of 1200 baud) for narrowband radios.
This device is also interoperable with the “internal modem” mode supported by the SHX, TRxM, TXxM, RXxM, and SMX family products (to name a few), as well as the “mode switch 12” modem function of the NBEK evaluation/test board.

> The M48 modem chip takes this idea to a logical conclusion, providing additional functionality (user programmable functions such as “akn/repeat” mode, repeater operation, more extensive addressing, variable port baud rates and radio timing parameters, and deeper data buffers) combined with a more bandwidth efficient baseband coding system, to support a fully transparent 4800 baud link over any narrowband radio. The M48 approaches the capabilities of a dedicated industrial radio modem, at a much lower price

The M48 is additionally supported by a wide (and expanding) range of application solutions, from a simple PCB hosting the chip and a NiM footprint radio, up to a 500mW 458MHz band industrial product using the SFX2 transceiver in a robust aluminium extrusion housing

Evaluation & Application Boards

To further simplify the implementation of user designs, a number of application/demo boards are offered, with necessary connectors and support and interface circuitry.
The TDL family has the TDi2 evaluation board (adding an SMA RF connector, an RS232 buffer with D9 connector, and power supply regulators) and the TDL eval board (which takes the TDi2 and adds sockets for the module and provision for an (optional) PP3 battery)

The external “modem” devices (most particularly the M48 chip) have an extremely wide range of applications boards, combining the bare chip with connectors, interface buffers and an extensive choice of Radiometrix wireless modules
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