Updated for firmware 3.00.00 (first published 02.01.2025).

1. Introduction

Wireless M-Bus (wM-Bus) is a widely used protocol for smart metering applications, enabling efficient data transmission from utility meters to data collection systems. However, in large industrial sites, urban environments, or buildings with thick walls, signal coverage can become a challenge. Every STG Series gateway can work as a WMBus Repeater: it sends received WMBus frames to the air again, so that a receiver outside the range of the meters can still read them.

2. Why Extend the Wireless M-Bus Range?

1. Overcoming Signal Obstacles – Buildings with thick walls, basements, or underground installations can weaken the signal.

2. Covering Large Areas – Industrial sites, smart cities, and large residential complexes require extended range.

3. Improving Data Reliability – Weak signals lead to data loss, increasing transmission retries and power consumption.

4. Reaching distant meters – the repeater sends their frames to the air again, so that a receiver outside their range can still read them.

3. How the STG Series Repeater Function Works

Select WMBus Repeater as the Device Function on the Operating Mode page.

1. Reception – the repeater receives the WMBus frames of the meters in the selected reception mode (S - Mode, T - Mode or C / T - Mode ( combined reception of T and C Mode messages )). No meter list is needed and the number of meters is not limited; only the white list / black list decides which meters are repeated.

2. Delay – each frame is sent again after a random delay of 5 to 25 seconds; up to 16 frames wait for their delay at the same time.

3. Sending – frames are transmitted with the Tx Package Transmission Mode (S, T or C mode) and the Tx Power Level (-1 dBm to 13 dBm) of the WMBus Settings page.

4. No loops – in a frame that carries a hop bit the repeater sets this bit before it sends the frame; a frame whose hop bit or repeated-access bit is already set is not sent again, so two repeaters do not feed each other. A frame without a hop bit that was already repeated is not repeated again within 60 seconds.

5. Repeater address – the repeater sends its own SND-NKE telegram 2 to 5 seconds after it has repeated an installation telegram of a meter, unless Repeater Manufacturer ID (hex) and Repeater Device ID (hex; both IDs 0 = SND-NKE off) are both 0.

Keep the AES keys of the meters out of the repeater: a meter whose key is entered is repeated decrypted, and the receiving gateway cannot read it. The keys belong in the gateway that reads the meters.

The repeater works without an Ethernet connection; the network is needed for the web interface only. MQTT and Modbus are not available in this function.

4. Benefits of Using STG Series Repeaters

✔ Extended Range – a receiver outside the range of the meters can still read them.

✔ Stand-alone operation – no Ethernet connection and no meter list needed.

✔ Easy Deployment – simple setup with configurable parameters: transmission mode, output power, filters.

5. Use Cases

• Smart Metering in Residential and Commercial Buildings

• Industrial Facilities with Wireless Monitoring

• Smart Cities and IoT Deployments

• Water, Gas, and Electricity Metering Networks

6. Conclusion

Extending the range of Wireless M-Bus devices is crucial for ensuring uninterrupted data transmission in large or complex environments. The STG Series by REDZ provides an efficient Repeater Function, offering a cost-effective, reliable, and easy-to-deploy solution for smart metering and IoT applications.

The repeater function is described in chapter 9.7 "Scenario 6 - WMBus repeater" and chapter 10.6 "WMBus Settings" of the STG user manual.