Crossfire – LQ explained

“What’s the difference between LQ and RSSI?” or “Which one should I use?”
are frequenly asked question by first time Crossfire users.
The answer to which one should be used along with Crossfire is pretty easy: always use LQ

LQ = link quality  –  “How good is my link?”
RSSI = relative signal strength index  –  “How loud is my transmitter?”

RSSI just tells you how much signal strength is on the frequency.

LQ takes into account both the RSSI and noise floor, therefore giving you a more accurate indication of the control link stability.

Showing LQ on the BetaFlight OSD

With recent versions of BetaFlight (4.1 and above) it became even easier to show LQ on the OSD as it now comes with dedicated OSD elements:

OSD elements

(on previous versions you had to “route” LQ via an AUX channel and use the “RSSI” OSD element)

On BetaFlight 4.1 and later there’s nothing to set up.
Just use the LQ OSD element which is ranging from 0 to 300:

300-200 is the LQ of 150hz mode (= RFMD 2)
199-100 is the LQ of 50hz mode (= RFMD 1)
99-0 is the theoretical LQ of 4hz mode (= RFMD 0)

Preview: BetaFlight 4.2 OSD example showing dBm value and LQ (now split in RFMD and LQ number):

OSD example

When should I turn back?

Head home when LQ drops below 70 in RF Mode 1.

Why is LQ at 99 most of the time?

That’s because Crossfire is so good 😉 It has very sensitive “ears” and can listen through noise, deal with imperfections in the signal, etc.

More detailed explanation

RSSI simply determines the “volume” of your transmitter. It’s a logarithmic value, meaning you can still go very far, even if the number appears low): 60% RSSI doesn’t mean 60% range left.
It means about 90% range left. 5% would be about 30-50% range left.

Picture yourself in a desert … not a sound anywhere. A mile away someone has a boom-box.
RSSI is… let’s say… 50. You can hear it perfectly. LQ = 100.
Now you’re in a busy city. Same boombox. Same distance. RSSI still 50.
But you can’t even hear the boombox. LQ = 0.

RSSI in and of itself tells you absolutely nothing. It makes no indication of if you are going to failsafe, or how many packets are coming through. Based only on RSSI information you are unable to make any statement about your link budget, the quality of your link, how close you are to a failsafe, etc.

That’s why you want to monitor LQ instead of RSSI. RSSI is just for noisy situations.
For example: when the RSSI is strong but LQ fluctuates, you know you’ve got lots of interference/noise.

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