UHF Multi Channel Hi Power Radio Modem

Figure 1: TDH2-433-9 radio modemThe TDH2 is a 9600baud half-duplex multi channel OEM radio modem with a power output of 25mW. It is a 100% pin-compatible drop-in replacement for the Radiometrix TDL2A and can be used to replace the TDL2A in applications where greater radiated power is desired. TDH2 acts as a transparent serial cable to attached host. TDH2 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.

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 TDH2 can be set to 1 of 8 unique addresses. As well as having unique addresses, the TDH2 allows operation on one of 5 pre-set frequencies in the 433MHz band. These frequencies are non-overlapping and simultaneous operation of TDH2s in the same area on different channels will be possible. Units are supplied on 433.925MHz (Ch0) as default.


  • 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
  • Fully screened. Low profile
  • Available as TDH2T transmitter and TDH2R receiver for one way communication
  • Conforms to Australian/New Zealand AS/NZS 4268:2003


  • Handheld terminals
  • EPOS equipment, barcode scanners
  • Data loggers
  • Industrial telemetry and telecommand
  • In-building environmental monitoring and control
  • High-end security and fire alarms
  • GPS systems
  • Vehicle data up/download

Technical Summary

  • Operating frequency: 433.925MHz (default)
  • Modulation: 16kbps bi-phase FSK
  • Supply: 5V at 50mA transmit, 22mA receive/idle
  • Transmit power: +14dBm (25mW)
  • Receiver sensitivity: -105dBm (for 1% data error)
  • 32 byte data buffer
  • Transmit power-up time: <4ms
  • Size: 37 x 26 x 8mm

Evaluation Platform: TDL2A Evaluation Kit


Figure 2: TDH2 Footprint (Top of the unit) view

Pin Description - TDH2

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


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
50mA transmit
22mA receive/idle
Operating temperature -20 to +70 °C (Storage -30 to +80 °C)
Size 37 x 26 x 8mm
Regulation Compliant with Australian/New Zealand AS/NZS 4268:2003
Interface          user 9 pin 0.1" pitch
RF 3 pin 0.1" pitch
Output power +14dBm (25mW) +/- 1dB
TX on switching time <4 ms
Modulation type 16kbps bi-phase FSK
FM peak deviation +/-22kHz
TX spurious <-40dBm
Sensitivity -105dBm for 1% BER
image -40dB
spurious / adjacent channel -60dBm
blocking -80dB nominal
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)

Ordering information

Part Number Description Frequency band Maximum baud rate
TDH2-433-9 Half duplex modem 433.925 - 434.565 MHz 9.6kbps
TDH2T-433-9 Transmitter only 433.925 - 434.565 MHz 9.6kbps
TDH2R-433-9 Receiver only 433.925 - 434.565 MHz 9.6kbps
TDH2-433-4 Half duplex modem 433.925 - 434.565 MHz 4.8kbps
TDH2T-433-4 Transmitter only 433.925 - 434.565 MHz 4.8kbps
TDH2R-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