Skip to main content

Antenna Gain & Output Power

This page explains how transmit (TX) power works on a MikroTik LoRa gateway (R11e-LR8G / wAP LR8G kit) and how to configure the antenna-gain setting so the gateway stays within the legal radiated-power limit (EIRP).

Read this before attaching an external antenna

There is no "TX power" setting on the gateway. The card's only RF control is antenna-gain, and its factory default is 0. If you attach an antenna with gain and leave the default, the gateway will radiate above the intended power and can exceed the legal EIRP limit.

How TX power actually works​

A MikroTik LoRa gateway does not set its own transmit power. The value comes from the LoRaWAN Network Server and the gateway only compensates for the antenna:

radio output (at the connector) = server_value − antenna-gain
radiated EIRP                    = radio output + antenna gain − cable loss
  • server_value — the TX power the Network Server requests, in dBm EIRP (Semtech UDP txpk.powe field). In ChirpStack this is downlink_tx_power in the region file (e.g. region_eu868.toml); -1 means "use the band maximum".
  • antenna-gain — a MikroTik gateway setting, in dBi. It is a subtraction, not a boost. It exists so that after the antenna adds its gain back, the radiated EIRP matches what the server asked for.
Counter-intuitive

A higher antenna-gain value produces lower power out of the radio. It is a compensation knob for regulatory compliance, not a way to increase range.

Configure antenna-gain​

Enter the real gain of the attached antenna in dBi, minus cable loss.

note

For the full list of LoRa parameters and their exact definitions, see the MikroTik documentation: LoRa General Properties.

WebFig / WinBox​

  1. Open LoRa in the left menu.
  2. Click the LoRa interface (e.g. lora1).
  3. Go to the General tab.
  4. Set Antenna Gain to the antenna's gain in dBi.
  5. Click Apply.

The Antenna Gain field in the WebFig / WinBox LoRa Device dialog

CLI (terminal / SSH)​

/lora print
/lora set [find] antenna-gain=2

On newer RouterOS builds the menu may be /iot lora instead of /lora. If /lora is not found, use /iot lora set [find] antenna-gain=2.

AntennaGainantenna-gain value
wAP LR8G kit built-in antenna (868 MHz)2 dBi2
MikroTik omni LoRa antenna kit (TOF-0809-...)6.5 dBi6.5
Other external antennasee its datasheetantenna dBi − cable loss

If the antenna gain is unknown, err on the higher side — the gateway will back off its power further and stay within legal limits.

Worked example (EU868)​

Downlink on 869.525 MHz, EIRP limit 27 dBm, 6.5 dBi antenna, server requests powe = 27:

antenna-gainRadio outputRadiated EIRPResult
0 (default)27 dBm33.5 dBm✗ 6.5 dB over the limit
6.520.5 dBm27 dBm✓ correct
4.5 (6.5 dBi antenna − 2 dB cable)22.5 dBm27 dBm✓ correct

Changing the transmit power itself​

Because the gateway takes its power from the Network Server, change the downlink TX power there — for example in ChirpStack, downlink_tx_power (dBm EIRP) in region_eu868.toml. The uplink TX power is a property of the end device (node firmware or ADR from the server), not the gateway.

To increase real-world range, use a better antenna and/or shorter, lower-loss cable — then update antenna-gain accordingly. The setting itself never adds power.

wAP LR8G kit — connect the internal antenna first

On the wAP LR8G kit the internal antenna is not connected from the factory. Attach it to the card's RFIO u.FL connector (with the device powered off) before use, or the card cannot transmit or receive over the antenna at all.

Regulatory limits (EU868)​

  • Uplink: max 25 mW = 14 dBm
  • Downlink on 869.525 MHz (RX2 band): up to 500 mW = 27 dBm EIRP
  • EIRP = TX power (dBm) + antenna gain (dBi) − cable loss (dB)

Always check the LoRaWAN Regional Parameters and your local regulations for the values that apply to your deployment.

Further reading​