The first rule hasn't changed. A transmitter and receiver only talk to each other on the same band. A 900 MHz receiver will not bind to a 2.4 GHz module, whatever the brand. The exception is dual-band hardware, which can work in either.
2.4 GHz: the default for good reasons
The ExpressLRS hardware guide recommends 2.4 GHz to new users unless they plan to fly hundreds of kilometres or in a very noisy environment. The reasons, according to the docs:
- Range is not the problem people think it is. The Signal Health page mentions over 40 km at 250 Hz and 100 mW on omnidirectional antennas. The hardware guide says 5 km is achievable on a ceramic-antenna receiver with no amplifiers at 250 Hz/100 mW with clear line of sight.
- Antennas are about 2.5 times smaller than 915 MHz ones. On a 5-inch or a whoop that settles it.
- More spectrum to hop around in, so more pilots can fly at once.
- The fastest packet rates. On 2.4 GHz you get F1000 and K1000 at 1000 Hz. In the 900 MHz table the only 1000 Hz rate is K1000 Full.
- Wi-Fi is less of a threat than it sounds. The docs say 2.4 GHz LoRa handles Wi-Fi noise very well.
900 MHz: for long range and obstacles
900 MHz is the original long-range band. The docs describe it as better at penetration and "the ultimate king of long range flying", while adding that the penetration difference may not be as great as you think. At the same packet rate its sensitivity limit is usually lower, which means it can still hear a weaker signal.
Sensitivity limits from the ExpressLRS 4.x table:
| Packet rate | 900 MHz | 2.4 GHz |
|---|---|---|
| 25 Hz | -123 dBm | - |
| 50 Hz | -120 dBm | -115 dBm |
| 100 Hz | -117 dBm | - |
| 150 Hz | - | -112 dBm |
| 200 Hz | -112 dBm | - |
| 250 Hz | -111 dBm | -108 dBm |
| 500 Hz | - | -105 dBm |
| F1000 (FLRC) | - | -104 dBm |
The price is size and noise. 900 MHz antennas are large and heavy for a small build. Wi-Fi does not bother this band, but the docs list other neighbours: cell towers, thermostats, fire and burglar alarms and anything else that transmits there. The band is narrow, which is why the docs ask pilots at races to use low power so they don't knock others out of the sky.
In Europe the band is 868 MHz, and the limits are low
900 MHz hardware comes in two versions: 868 MHz for the EU and 915 MHz for the US and other regions. In the ExpressLRS Configurator you pick the matching regulatory domain, Regulatory_Domain_EU_868. On 2.4 GHz there is Regulatory_Domain_EU_CE_2400 alongside the general ISM one. TX and RX must use the same domain, or they won't bind.
It's worth knowing what the European short range device recommendation (CEPT ERC/REC 70-03, edition of October 2025) actually allows:
| Band | Power | Duty cycle | Note |
|---|---|---|---|
| 863-870 MHz | 25 mW e.r.p. | up to 0.1% | frequency hopping |
| 869.4-869.65 MHz | 500 mW e.r.p. | up to 10% | narrow sub-band |
| 2400-2483.5 MHz | 100 mW e.i.r.p. | - | wideband data |
These are CEPT recommendations, and each country implements them in its own regulations, so check the Polish ones (UKE) before you rely on a table. Even so, the gap between a 1 W module and 25 mW is obvious.
The ExpressLRS docs also disagree with themselves on listen before talk. The firmware options page says the EU domains are now LBT compliant. The user defines page still says EU 868 is compliant in frequency, but not LBT compliant. Check the current notes in the Configurator for your version.
How to tell which band a device uses
Look at the antenna and the chip:
- SX1281 / SX128x: 2.4 GHz only. Small antennas.
- SX1276 / SX127x: 900 MHz only (868 or 915 MHz). Large antennas.
- LR1121: both bands. Antennas often have both 2.4 GHz and 900 MHz elements.
A dual-band receiver works with a 2.4 GHz module and with a 900 MHz module, and you can lock it to one band. On a dual-band transmitter you choose the band in the Lua packet rate list. Oscar Liang describes the options as "Low band" (868/915 MHz) and "2.4G".
Gemini: one band, two frequencies
Gemini needs a Gemini-capable transmitter with two RF paths and a true diversity receiver, which has two RF chips, each with its own antenna. The transmitter sends the same packet on two frequencies at once, about 40 MHz apart on 2.4 GHz and about 10 MHz apart on 900 MHz. The receiver catches both, so the chance that at least one gets through goes up.
Gemini combines with DVDA modes. D500 on its own sends two copies of each packet on two frequencies. With Gemini you get four copies on four frequencies.
What it gives you:
- higher, more stable LQ in a noisy environment: urban freestyle, races with six or eight pilots and radios left on in the pits;
- stronger telemetry, because both antennas on the transmitter listen for it, even when the module is not in Gemini mode.
What it does not give you: range. The ExpressLRS docs say this plainly. Sensitivity for the packet rate stays the same, so Gemini holds LQ up to the failsafe point, but failsafe happens at roughly the same distance.
Gemini only works with a true diversity receiver. With a single-antenna receiver or a simple antenna diversity one (one chip, two antennas), the receiver syncs to one of the two transmitter paths and the other just transmits for nothing. Oscar Liang advises setting a specific antenna (e.g. ANT1) in that case and not enabling Gemini. According to the ExpressLRS docs, version 4.0 manages this automatically, based on which receiver is in sync.
Gemini Xrossband: both bands at once
Gemini Xrossband (GemX) sends the packet in 900 MHz on antenna 1 and in 2.4 GHz on antenna 2. It needs a transmitter with two LR1121 chips and a GemX-capable receiver. A single-band receiver won't even get sync.
You turn it on by choosing an X rate in the Lua (X100 Full or X150). The antenna mode then locks to Gemini, because both paths have to work at once. The sensitivity limit for both X rates is -112 dBm.
Oscar Liang gives the Radiomaster GX12 radio and the BetaFPV SuperX Nano receiver as an example of a compatible pair. In one place his guide lists maximum range among GemX's advantages, but further down he writes that Gemini doesn't magically increase maximum range, and the ExpressLRS docs say the same. What you're paying for is redundancy. The range is set by the packet rate and the band.
What to buy
5-inch freestyle, racing, whoops: a 2.4 GHz receiver. According to Oscar Liang, a single antenna is more than enough for most freestyle and indoor pilots. For longer flights he suggests a diversity receiver with the antennas mounted in different places on the frame.
7-inch and longer flights: many pilots go for 900 MHz, but Oscar Liang writes that 2.4 GHz is often more than enough and recommends trying it first if you already have a 2.4 GHz transmitter. A lower packet rate gives you more margin. Move to 900 MHz only when you can see what 2.4 GHz can't do on your routes, and remember the 868 MHz power limits.
Flying in a city or at busy races: Gemini on 2.4 GHz with a true diversity receiver. Higher LQ in noise, not more range.
Buying a new module or radio: dual band with GemX support gives you the most freedom. Oscar Liang recommends this: you'll be compatible with virtually all ExpressLRS receivers on the market. You pay for that flexibility up front.