Embedded Radio ModemMU-4-434

The MU-4-434 is an embedded radio modem operated in the 434 MHz ISM band designed as the successor to the MU-2-R with improved in-band blocking performance. Dedicated commands, designed for wireless applications, are provided for building a range of wireless system, from simple control systems to wide network systems. Using the commands, the user can concentrate on designing the application without needing to be aware of the radio protocol and control aspects. Reed-Solomon code is used for forward error correction (FEC) to maintain data integrity and provide highly reliable wireless communication. The MU-4-434 meets the requirements of the European RED and UK Radio Equipment Regulations 2017, carries the CE marking and UKCA marking.
The relay feature allows you to extend the range by using additional units (up to 10 units)


  • UART interface with simple command protocol compatible with MU-2-R
  • 434 MHz ISM band Pre-programmed 127 channels
  • 10 mW / 1 mW power selectable
  • Forward error correction with Reed Solomon coding
  • Repeater and auto answer back function
  • Target station receive signal and noise level acquisition
  • Low power operation 42 mA at 3 V / TX
  • Transparent mode
  • RED compliant (EN300 220)
  • Radio Equipment Regulations 2017 (UK)
  • 429 MHz version available (Japan)

Serial Data Transmission with Simple, Dedicated Commands

The MU-4-434 uses Circuit Design’s unique simple, dedicated commands. Setting channels and all other controls can all be performed with commands.

Example 2: Changing the channel to 08
Note: The command transmission is the same for MU-2-R, however there exists timing differences between
MU-2-R and MU-4-434

Relay Function (Maximum 10 Stations)

You can make a relay with a maximum of 10 stations using the route command.

Example of transmitting data (ABCDE) to the target station with Equipment ID EI=04 via relay station 1 (EI=02) and relay station 2 (EI=03).

MU-4-434 and MU-2-R should not be used together when using relay or ACK function. For more information, please contact Circuit Design.

Reed Solomon Coding

One of several FEC block codes, it has strong error correction ability and the characteristic of correcting data errors caused by burst noise. Reed-Solomon codes are used in compact disks, satellite communications, and digital TV broadcasting

MU-4-434 FEC

The MU-4-434 uses Reed-Solomon code for FEC, which reduces errors occurring due to burst noise and/or noise at low received signal level, and it improves the receive sensitivity of the equipment by more than 5 dB *1.

Error correction protocol data format   *2 MU-4-434 data block
MU-4-434 data component: 1 to 255 bytes variable User data Parity
Reed-Solomon code specification Code: RS (255, 247) 1 - 32 bytes 8 bytes
Primitive polynomial: X8 + X4 + X3 + X2 + 1 33 - 64 bytes 8 bytes
Interleave: None : :
Error correction rate: 10% error or more 224 - 225 bytes 8 bytes

*1 In interleave mode / Measured at Circuit Design, Inc.
*2 There are operation modes with or without error correction. Select the appropriate mode depending on the situation at the site and the application

How, When Does FEC Help RF Communication

VS Error in burst noise (Measurement conditions: 4,800 bps / Data size 4 bytes)

Error correction reduces influence from noise with is generated suddenly or is continuously generated at a dead point during mobile use with multi path.

VS Error in random noise (Measurement conditions: 4800 bps / Data size 32 bytes / Received signal level -114 dBm)

Error correction reduces influence from random noise which appears at a low received signal level

Target Station Receive Signal and Noise Level Acquisition

It is possible for the main station to acquire the signal and noise level of the target station some distance away. By using these values (and therefore calculating SNR), it is possible to evaluate the communication conditions during installation.


  • Telemetry - Environment monitoring, Meter reading, Various measuring applications
  • Telecontrol - Remote control for industrial equipment
  • Security - Various alarm and monitoring systems



Parameter Specification Remarks
Applicable standard RED compliant (EN 300 220)
UK Radio Equipment Regulations 2017
CE marking and UKCA marking acquired
Communication method Half-duplex, one-way, broadcast
Oscillation system PLL synthesizer system
Emission type F1D Binary FSK
Frequency 433.200 to 434.775 MHz
Number of channels 127 channels 12.5 kHz step
RF bit rate 4,800 bps
RF output power 10 mW / 1 mW Nominal, Contact (50 Ω)
Receiver sensitivity -113 dBm Transparent mode, BER 0.1%
Error correction system Reed-Solomon code RS (255, 247)
Supply voltage 3.0 to 5.0 V DC Absolute maximum rated voltage 5.5 V
Supply current Transmitting: 42 mA
Receiving: 22 mA
10 mW at 3 V
Transmitting: 26 mA
Receiving: 22 mA
1 mW at 3 V
Operating temperature range -20 to +65 ºC The operation distance varies with the temperature conditions.
Dimensions 36 × 26 × 8 mm Not including the antenna.
Weight 14.5 g

Reference data
* Effective radio communication speed: About 3,400 bps / Conditions: One-way communication, no error correction, 25 ºC
* Range: About 600 m / Conditions: One-way communication, no error correction, 25 ºC, line of sight distance, ground level of 1.5 m, vertical antenna


UART Interface

Parameter Specification Remarks
Communication method Serial communication RS232C format
Synchronization Asynchronous
UART bitrate 1,200 / 2,400 / 4,800 / 9,600 / 19,200 / 38,400 / 57,600 bps
Other parameters Data length 8 bits, no parity, 1 or 2 stop bits

External View

Operation Guide

Version 4.0

Parts Change Notice (PCN)

PCN2391001 (Oct. 2023)

Supplementary Information

Demonstration video for Temp Humidity Sensor using MU-2-429 module
Demonstration video for Temp Humidity Sensor and MU-2-R
Embedded radio modem, MU-2-R 434 MHz
Differences between MU-4-434 (434 MHz) and MU-4-429 (429 MHz) PDF


Operation Guides

Version 1.0 (MU4-RS2IF) PDF
Version 1.0 (MU4-USBIF) PDF


Operation guide

MU-2-R Evaluation Software Program (Version 1.1)

Evaluation Program

Evaluation program* for MU-4-434 and driver

* The evaluation software for MU-2-R can be used to evaluate the MU-4-434

Supplementary Information

Demonstration of evaluation software for embedded radio modem MU-2-R

Test Board for MU-4-434

RS232 Interface Board : MU4-RS2IF

The MU4-RS2IF is an RS232 interface board for testing MU-4-434 module. It can connect to the COM port of PC or PLC through the D-Sub-9 pin connector. The board is equipped with transmit, receive LED, power supply terminal, main switch and initialisation button.

The module can be used with coax extension cable to allow optimum placement of the antenna according to the environment. Click here for more details.

This test board does not include the modem MU-4-434. Please order if necessary.


  • Connection to PC COM port for data communication and module control
  • Using RS232 cable, extension to tens of meters possible.
  • Evaluation program available

External View

USB Interface Board : MU4-USBIF

The MU4-USBIF is a USB interface board for testing MU-4-434 module. It can connect to the COM port of PC or PLC through USB. The board is equipped with transmit, receive LED, power supply terminal and main switch.

The module can be used with coax extension cable to allow optimum placement of the antenna according to the environment. Click here for more details.

This test board does not include the modem MU-4-434. Please order if necessary.


  • Connection to USB port for data communication and module control
  • Evaluation program available

External View

Evaluation Program: MU2-ESP

The MU-4-434 can be tested using the MU2-ESP evaluation program. The description of the functions in the evaluation program is listed below. To download the evaluation program, please click here.

Air Monitor

Spectrum Domain

This displays the receive level of each frequency channel within the band as a simple spectrum. You can monitor the noise and the state of interference in the field. You can also display the information for the target station.

Time Domain

This records the receive level of specific channels in a time base. You can monitor changes in the field strength due to the communication distance and environment of use.

Control Window

You can issue commands and perform controls.

Test Window

You can perform packet success rate tests and acquire the internal setting values.

Communication Test

Using an RS-232C conversion board, you can perform RS232C communication tests between PCs.

Text Transmission
File Transmission



Lead antenna with plug

...more info


Rigid antenna with plug

...more info


Coaxial cable

...more info


434MHz antenna with extension coaxial cable for the receiver

...more info


BNC Connector conversion cable

...more info


Water Resistant Antenna Cover

...more info


TMP-SMA conversion cable

...more info

RF modem using LoRa® in the 429 MHz band: Machine monitoring system


The system is capable of obtaining information about various machines in the factory while forwarding it to a central management system in order to visualise their status and in realtime. Collected data can be exported to CSV file and if a machine stops for any reason, it is possible to notify by email to the operator automatically. By using the long range SLR-429M LoRa modem operating in the 429 MHz band for machine monitoring, large scale cable installation for communication is not required. Such IoT system can be introduced in a short time and at low cost.

KANTARO system to detect ground slope collapse - transmitting the sensor data by wireless


Gradual shifts in tilt can occur in natural or artificial ground slopes due to factors such as looseness and slipperage. The KANTARO was developed for capturing such shifts.

Measurements from the tilt sensor driven into the ground slope are taken at regular intervals. Changes in the tilt and the speed of change are determined and the level of risk evaluated. The data from the tilt sensor and information that could indicate imminent ground collapse can be transmitted quickly by radio making this useful in disaster prevention.

Remote monitoring using long range wireless communication - System for monitoring sewage manhole pump

MU-3-429, MU-2-429

In the case where problems occur in infrastructure essential to daily living such as the sewage system's water level or pump, a swift response is required. The ICT sewage monitoring system that uses low power radio makes this possible. By using long range wireless communication for monitoring, it is possible to identify the source of the problem as soon as it occurs. This allows the sewage system to be operated and maintained safely.