How RSSI and LQ Actually Work on ExpressLRS: A Simple Guide for RC Makers

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Introduction to RSSI and LQ on ExpressLRS

If you’re into RC flying or building your own radio gear with ExpressLRS (ELRS), you’ve probably come across the terms RSSI and LQ. These two signals are crucial for understanding your radio link quality, but how do they really work under the hood? Let’s break it down in a simple way that helps you get the most from your gear.

What is RSSI?

RSSI stands for Received Signal Strength Indicator. It’s a measurement of how strong the radio signal is at the receiver’s side. In ELRS, RSSI tells you how powerful the signal your receiver is getting from the transmitter.

Here’s what you need to know about RSSI in ExpressLRS:

  • Measured in dBm: RSSI values are typically given in negative dBm numbers (like -60 dBm). The closer to zero, the stronger the signal.
  • Direct RF measurement: The receiver’s radio hardware measures the signal power of the incoming packets.
  • Instantaneous but fluctuates: RSSI can vary quickly based on obstacles, distance, and interference.

In practical terms, a high (less negative) RSSI means your receiver is getting a strong, clean signal from the transmitter, which usually translates to better control and video quality.

What is LQ (Link Quality)?

LQ stands for Link Quality, and it’s a bit different from RSSI. Instead of just measuring signal strength, LQ reflects how good the overall communication link is between the transmitter and receiver.

Key points about LQ on ExpressLRS:

  • Based on packet success: LQ is calculated by the receiver looking at how many data packets are received correctly versus how many are lost or corrupted.
  • Expressed as a percentage: LQ often runs from 0% (no link) to 100% (perfect link).
  • Accounts for interference and noise: Even if RSSI is high, a noisy channel can lead to lower LQ due to packet errors.

So, while RSSI tells you "how loud" the signal is, LQ tells you "how clean" and reliable the communication is.

How RSSI and LQ Work Together in ExpressLRS

In ELRS, both RSSI and LQ are crucial for maintaining a reliable RC link:

  • RSSI helps the system adjust power: If RSSI drops too low, the transmitter or receiver might increase power or warn the pilot.
  • LQ informs the pilot’s display: Many ELRS radios and OSDs display LQ to show how well your control signals are getting through.
  • Failsafe triggers: The system can use LQ thresholds to decide when to trigger failsafe or return-to-home functions.

ExpressLRS firmware constantly monitors these values, updating hundreds of times per second, so your link stays as strong and reliable as possible.

Using RSSI and LQ in Your Builds

For UK-based makers and RC pilots, knowing how to interpret RSSI and LQ can help you:

  • Choose the best antenna placement for stronger RSSI.
  • Diagnose interference issues if LQ is low despite good RSSI.
  • Set sensible failsafe points to protect your models.
  • Improve firmware settings and power output for longer range.

Many ELRS receivers output RSSI as a PWM or analog voltage signal, which you can feed into your flight controller or OSD for real-time monitoring. LQ is usually sent back via telemetry for display on your transmitter.

Conclusion

Understanding RSSI and LQ on ExpressLRS gives you a clearer picture of your radio link’s health. RSSI shows signal strength, while LQ reflects how well your data packets are getting through. Together, they help you fly safer and build better radio systems. Keep an eye on both when tuning your setup, and you’ll enjoy smoother flights and fewer surprises.

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