Change the coordinator transmit power

Introduction

The transmit power (TX power) is the power, in dBm, at which the coordinator sends its radio frames. +3 dBm is twice the power, -3 dBm half of it.

By default the plugin doesn’t set it: the coordinator keeps its own. You can raise or lower it with the TXpower_set setting. Before you do, keep in mind that a Zigbee link works in both directions, and that the TX power only changes one of them.

This page describes the plugin from stable9 9.1.008. For the change from older versions, see Upgrading from 9.1.007 or older.

What more power brings

• Longer direct links from the coordinator. Devices further away, or behind a wall, hear it better.
• Fewer hops for the routers close to the coordinator, so a little less latency.
• A workaround for a coordinator placed badly (in a cupboard, next to the computer, behind metal).

What less power brings

• Less interference with your own Wi-Fi and with your neighbours’ networks. See Zigbee and Wi-Fi.
• Compliance with your country’s rules. The limits apply to the radiated power, antenna gain included, and differ between regions. zigpy, the library the plugin uses for its coordinators, treats 8 dBm as safe in every region.
• A mesh that relies on routers instead of on many weak direct links to the coordinator.

What it costs

More power is not always better:

• It doesn’t improve reception. The coordinator hears the devices no better than before. A battery device transmits with low power: it may hear the coordinator and still fail to answer it. The link then works in one direction only, which looks like a device that “sometimes” responds.
• More end devices pick the coordinator as their parent, because it looks like the strongest router around. The coordinator can only hold a limited number of direct children, which depends on the chip and firmware (see Compatible coordinators). Over that limit, new devices fail to join or keep rejoining.
• Devices may change their parent after the change, so expect the network to settle for a while.
• It may be outside what your country allows. See What less power brings.

To cover a large house, adding routers (mains-powered devices) is usually more effective than raising the coordinator’s power.

Increase or decrease

Both are possible on Texas Instruments and Silicon Labs coordinators:

• the value is a whole number of dBm, negative values included (for example -5 or 10);
• 0 means “keep the coordinator’s own power”, so exactly 0 dBm can’t be requested: use -1 or 1;
• at start, values above 20 dBm are lowered to 20 dBm. A change from the WebUI is limited to the range -22 to +22 dBm;
• the firmware may lower the value further, to what the chip supports. See the maximum power of common chips.

ConBee / RaspBee (deCONZ) and BLZ coordinators don’t support it. On a ZiGate V1 it can only be lowered.

Coordinators and what they support

Silicon Labs: the saved value

A Silicon Labs stick keeps the last power it was given, even after the plugin stops setting one:

• setting TXpower_set back to 0 does not bring the default back: the stick stays at the last value. To return to the default of the radio library, set 8;
• when the stick forms or restores a network without a TX power, it uses 8 dBm;
• the plugin sets 8 dBm once on a stick that an older plugin version left at 0 dBm (see Upgrading from 9.1.007 or older).

Maximum power of common chips

The firmware and the board (antenna, external amplifier) also matter: two sticks with the same chip don’t always reach the same range.

Change it with the plugin

1. Go to Settings, Coordinator settings, and show the advanced settings (see WebUI Settings).
2. Set TXpower_set:
   • Texas Instruments, Silicon Labs: the power in dBm, or 0 to keep the coordinator’s own;
   • ZiGate V1: one of the 4 levels in the list.
3. Click Validate.
4. On Silicon Labs and ZiGate V1, restart the plugin.

The Certification setting (CE or FCC) is only sent to ZiGate coordinators. It doesn’t limit the TX power of the other coordinators.

Check the power

At start, the plugin log shows:

Effective TxPower: 5, Max TxPower: 20

Effective TxPower is the value the plugin sets (None when TXpower_set is 0), and Max TxPower the upper limit.

On Silicon Labs, the Network settings block that follows also gives the power the stick reports (TX Power:). On the other coordinators this line shows None.

Upgrading from 9.1.007 or older

Up to 9.1.007, TXpower_set = 0, the default, forced the coordinator to 0 dBm at every start. On Silicon Labs it also forced a power mode (boost and alternate transmitter output). Installations that never changed the setting ran at 0 dBm.

From 9.1.008:

• with TXpower_set = 0, the plugin leaves the coordinator’s power alone;

• a Silicon Labs stick still at 0 dBm is set once to 8 dBm, the default of the radio library, at the first start. The log shows:

  Coordinator TX power is 0 dBm, left by an older plugin version: setting 8 dBm, the radio library's default. Set TX Power in the plugin settings to choose another value
  

• a Texas Instruments coordinator goes back to its firmware’s own power;
• with any other value, nothing changes.

The coordinator may then reach further than before. Some end devices may pick a different parent after the restart: give the network some time to settle.