UHF Multi Channel Transparent Data Link Transceiver

The TDL2A is a 9600baud half-duplex multi channel OEM radio modem in BiM2 footprint, operating on European 433MHz ISM band. TLD2A acts as a transparent serial cable to attached host. TDL2A is an intermediate level OEM radio modem which is in between a raw FM radio module like BiM2 and a sophisticated OEM radio modem like SPM2. It takes care of preamble, synchronisation, bit balancing and error checking along with automatic noise squelching.

Figure 1: TDL2A-433-9 radio modem

The TDL2A provides a half duplex link. Provided no two devices attempt to transmit simultaneously no further restrictions on data transmission need be made, as all transmit timing, valid data identification and datastream buffering is conducted by the unit. Synchronisation and framing words in the packet prevent the receiver outputting garbage in the absence of wanted RF signal or presence of interference. For multiple radio systems (polled networks) a TDL2A can be set to 1 of 8 unique addresses. As well as having unique addresses, the TDL2A allows operation on one of 5 pre-set frequencies in the 433MHz band. These frequencies are non-overlapping and simultaneous operation of TDL2As in the same area on different channels will be possible. Units are supplied on 433.925MHz (Ch0) as default.


  • Conforms to EN 300 220-3 and EN 301 489-3
  • High quality, stable crystal reference
  • Low noise synthesiser / VCO
  • SAW front-end filter
  • Multi-stage ceramic IF filtering
  • Single conversion superhet
  • Serial modem baud rate at 9600bps (half-duplex)
  • Addressable point-to-point
  • 5 serial select wideband channels
  • Data Present indication
  • Available as TDL2T transmitter and TDL2R receiver for one way communication


  • Handheld / portable terminals
  • PDAs, organisers & laptops
  • Industrial telemetry and telecommand
  • In-building environmental monitoring and control
  • Remote data acquisition system, data logging
  • Fleet management, vehicle data acquisition

Technical Summary

  • Operating frequency: 433.925MHz (default)
  • Modulation: 16kbps bi-phase FSK
  • Supply: 5V at 28mA transmit, 22mA receive/idle
  • Transmit power: +10dBm (10mW)
  • Receiver sensitivity: -107dBm (for 1% BER)
  • 32 byte data buffer
  • Adjacent channel rejection: 65db @ ±320kHz
  • Spurious emission: <-65dBm
  • Receiver Blocking: 84dB

Evaluation Platform: TDL2A Evaluation Kit

Figure 2: TDL2A block diagram

Figure 3: TDL2A Footprint (Top of the unit) view

Pin Description - TDL2A

18 GND Ground
17 Vcc 5V (regulated power supply)
16 ENABLE Enable or DTR (5V CMOS logic level input)
15 SETUP Test/Setup mode selection
14 TXD Transmit Data (Inverted RS232 at 5V CMOS logic level)
13 NC No pin
12 RXD Receive Data (Inverted RS232 at 5V CMOS logic level)
11 STATUS Busy or CTS (5V CMOS logic level output)
10 GND Ground

RF GNF Pin 1 & 3
RF Ground pin, internally connected to the module screen and pin 8, 9, 10 and 18 (0V). This pin should be connected to the RF return path (e.g. co-axial cable braid, main PCB ground plane, etc).

RF Pin 2
RF 50W RF input/output from the antenna, it is DC isolated internally. (see antenna section for details)

GND Pin 8, 9, 10 and 18
Supply ground connection to ground plane and can.

Vcc Pin 17
5V voltage regulator should be used to have a clean 5V supply to the module. A 4V regulator is used inside for radio circuitry.

Active low Enable pin. It has a 47kW pull-ups to Vcc. It should be pulled Low to enable the module.
This can also be connected to DTR pin (only if it is asserted by the host) of an RS232 serial port via a MAX232 or equivalent RS232-CMOS level converter. 

SETUP Pin 15
Active low input to enter configuration or diagnostic test mode. It has a 47kW pull-ups to Vcc

TXD Pin 14
This is inverted RS232 data input at 5V CMOS logic level. It can be directly interfaced to data output of a UART in a microcontroller or to a TXD pin of an RS232 serial port via a MAX232 or equivalent RS232-CMOS level converter. TXD does not have an internal pull-up. If TDL2A is used in Receive only mode, TXD should be tied to Vcc.

NC Pin 13
There is no pin in this position.

RXD Pin 12
This is inverted RS232 data output at 5V CMOS logic level. It can be directly interfaced to data input of a UART in a microcontroller or to a RXD pin of an RS232 serial port via a MAX232 or equivalent RS232-CMOS level converter.

This pin goes high when valid data is present in the receive buffer. It can be used to trigger an interrupt in the host to download received data packet instead of waiting for it. It can be also be used as a primitive CTS signal. It is inverted RS232 data output at 5V CMOS logic level. It can be directly interfaced to an input of a microcontroller as a Data Detect (DD) or to CTS, DSR, DCD pins of an RS232 serial port via a MAX232 or equivalent RS232-CMOS level converter. This is can only be used to prevent host from uploading any data before downloading already received data, because transmission is prioritised over reception and any data to be transmitted will erase received data which is in the common buffer

Condensed specifications

Frequency 433.925MHz - CHAN0 (default channel)
433.285MHz - CHAN1
433.605MHz - CHAN2
434.245MHz - CHAN3
434.565MHz - CHAN4

Frequency stability

+/- 10kHz
Channel width
Number of channels
1 of 5, user programmed
Supply              voltage
28mA transmit
22mA receive/idle
Operating temperature -20 to +70 °C (Storage -30 to +70 °C)
Size 33 x 23 x 7mm
Spurious radiations Compliant with ETSI EN 300 220-3 and EN 301 489-3
Interface            user 9 pin 0.1" pitch
RF 3 pin 0.1" pitch
Output power 10dBm (10mW) +/- 1dB
TX on switching time <4 ms
Modulation type 16kbps bi-phase FSK
FM peak deviation +/-25kHz
Adjacent channel TX power <-37dBm
TX spurious <-45dBm
Sensitivity -107dBm for 1% BER
image -50dB
spurious / adjacent channel -65dBm
blocking -84dB nominal, 75dB worst case
LO re-radiation <-60dBm
Data rate 9600baud, Half duplex
Format 1 start, 8 data, 1 stop, no parity
Levels 5V CMOS (inverted RS232. Mark = 5V = idle)
Buffers 32 byte FIFO
Flow control None ('RX busy' pin provided)
Addressing 1 of 8, user programmed
Data latency 14ms (first byte into TX to first byte out of RX)

Operating principle of internal modem

To connect to a true RS232 device, inverting RS232-CMOS level shifters must be used. Maxim MAX232 or equivalent are ideal, but simple NPN transistor switches with pull-ups often suffice. With typical microcontrollers and UARTs, direct connection is possible.

Operation: The radio/data stream interface

A 32 byte software FIFO is implemented in both transmit and receive sub-routines. At the transmitting end this is used to allow for the transmitter start up time (about 3ms), while on receiving it buffers arriving packets to the constant output data rate. All timing and data formatting tasks are handled by the internal firmware. The user need not worry about keying the transmitter before sending data as the link is entirely transparent.

For transmission across the link data is formatted into packets, each comprising 3 bytes of data and a sync code. If less than 3 bytes are in the transmit end FIFO then a packet is still sent, but idle state replaces the unused bytes. When the transmit end FIFO is completely emptied, then the transmitter is keyed off .

Operation: Radio interface

Raw data is not fed to the radios. A coding operation in the transmit software, and decoding in the receiver, isolate the AC coupled, potentially noisy baseband radio environment from the datastream.

The radio link is fed a continuous tone by the modem. As in biphase codes, information is coded by varying the duration consecutive half-cycles of this tone. In our case half cycles of 62.5ms and 31.25ms are used.

In idle (or 'preamble') state, a sequence of the longer cycles is sent (resembling an 8KHz tone).

A packet comprises the Synchronising (or address) part followed by the Data part, made up of twelve Groups (of four half cycles duration). Each Group encodes 2 data bits, so one byte is encoded by 4 Groups.

Figure 4: TDL2A transmitting and receiving
The oscilloscope screen capture shows a single byte being transmitted by TDL2A. A BiM2-433-64 transceiver is used to capture the transmitted data.

The character appears on the serial data output (RXD) pin of the other TDL2A after about 12.5ms. Busy (STATUS) pin is momentarily set high to indicate the presence of a valid data in the receive buffer of the TDL2A.

It can be clearly seen that unlike raw radio modules, TDL2A does not output any noise when there is not any transmission. Data fed into the TXD input of a TDL2A appears at the RXD output of another TDL2A within radio range in the original form it was fed.

Figure 5: 16kbps Bi-phase encoded continuous data stream (expanded view)
Continuous serial data at 9600bps (above) is encoded as half-cycles of 8kHz (62.5ms long bit) and 16kHz (31.25ms short bit).

Programming the TDL2A

In order to use all the functions embedded in the TDL2A, the user must be aware of the setup/programming facility, which allow different addresses and and frequency channels to be set up, and if necessary accesses diagnostic test modes.

The TDL2A is programmed through the same RS232 port that is used for sending/receiving data. An RS232 terminal emulator (such as Aterm or HyperTerminal) is an ideal tool.

To enter program mode, the SETUP pin must be pulled low. In this mode the radio link is disabled, but characters sent (at 9600 baud, as normal) to the unit are echoed back on the RXD pin.

The unit will only respond to certain command strings:


These commands set up one of 8 unique addresses. A TDL2A will only communicate with a unit set to the same address.

CHAN0 to CHAN4 <CR><LF> These commands select one of 5 preset channels

A TDL2A will only communicate with a unit set to the same address and the same channel.

Address and channel numbers are stored in volatile memory. On power-up the TDL2A reverts to the default in EEPROM (as supplied this is always address 0 and Channel 0)

SETPROGRAM <CR> Writes the current set address into EEPROM as the new default.
A tilda character (~, ascii 126dec) sent by the unit indicates end of EEPROM write sequence
(these commands are normally only used for factory diagnostics)
NOTONE <CR> Transmit unmodulated carrier
LFTONE <CR> Transmit carrier modulated with 8KHz squarewave
HFTONE <CR> Transmit carrier modulated with 16KHz squarewave
# <CR> Transmitter off

A Carriage Return '<CR>' (00Dhex) should be entered after each command sequence to execute it.
Releasing the SETUP pin to high state returns the TDL2A to normal operation

Interfacing a microcontroller to TDL2A

Figure 6: TDL2A interfaced directly to a microcontroller

TDL2A can be directly interfaced to any microcontrollers. If the microcontroller has a built-in UART, it can concentrate on its main task and leave the packet formatting, bit balancing and error checking of serial data to TDL2A.

Serial data should be in the following format:
1 start bit, 8 data bits, no parity, 1 or 2 stop bits
0V=low, 5V=high

STATUS pin can be connected to one of the port pins which can generate an interrupt on low-to-high transition (e.g. RB0/INT pin in the PIC). This can be used to enter a receive sub-routine to download data received from remote TDL2A. Therefore, the host does not need to wait in a loop for a packet.

Range test and site survey can be carried out by connecting an LED on the STATUS pin. Every time, TDL2A is within range to receive valid data, the LED will flicker.

Interfacing RS232 port to TDL2A

Figure 7:TDL2A interfaced to an RS232 port via an RS232 line driver/receiver

STATUS pin in this can be connected to CTS, DSR and DCD pin to simulate a flow control signal.
TDL2A is capable of continuously streaming data at 9600bps. Therefore, STATUS pin is not asserted to stop the Host from sending data as in normal RTS/CTS flow control method, but merely to warn the host that there is already data in the receive buffer which need to be downloaded before sending any more data.

Some DTE hosts assert DTR signal when they are active and this can be used via RS232 line receiver to enable TDL2A. Otherwise the ENABLE must be physically pulled-low to activate the TDL2A.

NOTE: An interface board (with MAX232 type buffer, 9 way D connector, 5V voltage regulator and SMA RF connector) is available. This board is 61mm x 33mm in size.

Antenna requirements

Three types of integral antenna are recommended and approved for use with the module:

A) Whip: This is a wire, rod, PCB track or combination connected directly to RF pin of the module. Optimum total length is 16cm (1/4 wave @ 433MHz). Keep the open circuit (hot) end well away from metal components to prevent serious de-tuning. Whips are ground plane sensitive and will benefit from internal 1/4 wave earthed radial(s) if the product is small and plastic cased

B) Helical: Wire coil, connected directly to RF pin, open circuit at other end. This antenna is very efficient given it's small size (20mm x 4mm dia.). The helical is a high Q antenna, trim the wire length or expand the coil for optimum results. The helical de-tunes badly with proximity to other conductive objects.

C) Loop: A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and fed from RF pin at a point 20% from the ground end. Loops have high immunity to proximity de-tuning.

Ultimate performance
Easy of design set-up
Immunity proximity effects

The antenna choice and position directly controls the system range. Keep it clear of other metal in the system, particularly the 'hot' end. The best position by far, is sticking out the top of the product. This is often not desirable for practical/ergonomic reasons thus a compromise may need to be reached. If an internal antenna must be used, try to keep it away from other metal components, particularly large ones like transformers, batteries and PCB tracks/earth plane. The space around the antenna is as important as the antenna itself.

Figure 8: Antenna types

Ordering information

Part Number Description Frequency band Maximum baud rate
TDL2A-433-9 Half duplex modem 433.925 - 434.565 MHz 9.6kbps
TDL2T-433-9 Transmitter only 433.925 - 434.565 MHz 9.6kbps
TDL2R-433-9 Receiver only 433.925 - 434.565 MHz 9.6kbps
TDL2A-433-4 Half duplex modem 433.925 - 434.565 MHz 4.8kbps
TDL2T-433-4 Transmitter only 433.925 - 434.565 MHz 4.8kbps
TDL2R-433-4 Receiver only 433.925 - 434.565 MHz 4.8kbps

Limitation of liability

The information furnished by Radiometrix Ltd is believed to be accurate and reliable. Radiometrix Ltd reserves the right to make changes or improvements in the design, specification or manufacture of its subassembly products without notice. Radiometrix Ltd does not assume any liability arising from the application or use of any product or circuit described herein, nor for any infringements of patents or other rights of third parties which may result from the use of its products. This data sheet neither states nor implies warranty of any kind, including fitness for any particular application. These radio devices may be subject to radio interference and may not function as intended if interference is present. We do NOT recommend their use for life critical applications.
The Intrastat commodity code for all our modules is: 8542 6000.

R&TTE Directive

After 7 April 2001 the manufacturer can only place finished product on the market under the provisions of the R&TTE Directive. Equipment within the scope of the R&TTE Directive may demonstrate compliance to the essential requirements specified in Article 3 of the Directive, as appropriate to the particular equipment.
Further details are available on The Office of Communications (Ofcom) web site:
Licensing policy manual