As ExpressLRS continues to evolve, there are actually an awesome variety of receivers to select from. That’s why I created this information: to interrupt down the fundamentals of ExpressLRS receivers, clarify the distinction in frequency, antenna modes and options, and make clear compatibility with transmitters so you may resolve which receiver is finest on your wants.
For those who’re new to ExpressLRS, take a look at my in-depth tutorial on getting began and organising your radio hyperlink: https://oscarliang.com/setup-expresslrs-2-4ghz/
Frequency: 2.4GHz vs 900MHz
Most ExpressLRS receivers help one frequency band (both 2.4GHz or 900MHz), whereas some receivers help dual-band (each 2.4GHz and 900MHz), although they can be switched to a single frequency if you happen to favor.
2.4GHz
- The commonest frequency in FPV radio hyperlinks
- Gives glorious vary (tens of kilometers in best circumstances), satisfactory for many pilots
- Helps extra pilots flying on the identical time because of the broader bandwidth
- Compact antennas — best for FPV drones the place weight and house matter
900MHz
- Covers 868MHz (EU) and 915MHz (US/remainder of the world) — it’s essential to select the proper frequency on your area to keep away from interference
- As a result of decrease frequency, it’s higher in penetration and vary in comparison with 2.4GHz, most well-liked for long-range flights
- Drawbacks: bigger antennas and added weight, which might be a problem for smaller builds
For many pilots, 2.4GHz is ample. 900MHz is highly effective, however typically overkill until you’re particularly flying lengthy vary or in difficult environments.
The best way to Determine 2.4GHz and 900MHz Receivers
You possibly can often inform what frequency a receiver helps by simply trying on the antenna:
- 2.4GHz receivers → Very small antennas; solely work with 2.4GHz transmitters
- 900MHz receivers → Massive antennas; solely work with 900MHz transmitters
- Twin-band receivers → Antennas typically characteristic each 2.4GHz and 900MHz parts, permitting them to work with each transmitter varieties
 2.4Ghz |
 900Mhz |
 2.4Ghz + 900Mhz |
One other indicator is the RF chip used:
- Single frequency chips:
- SX128X (SX1281) → 2.4GHz
- SX127X (SX1276) → 900MHz
- Twin-band chip:
- LR1121 → Helps each 2.4GHz and 900MHz
Antenna Modes
I like to think about antenna modes in two classes: Fundamental Mode and Gemini Mode.
Fundamental Mode
Fundamental Mode
Fundamental mode is how radio hyperlinks conventionally works in FPV drones. The transmitter sends one packet at a time to the receiver.
Range
If the receiver has two antennas, it may possibly reap the benefits of range to enhance sign reliability.
The principle advantage of range is that you could mount antennas in numerous orientations or places on the drone. This helps:
- Optimize antenna alignment because the drone continually adjustments perspective in flight
- Eradicate sign blind spots
However there are two sorts of range, relying on the receiver {hardware}.
Antenna Range:
- 1 RF chip + 2 antennas
- The receiver robotically chooses whichever antenna has the stronger sign at that second
- Helps cut back sign dropouts brought on by antenna orientation or multipath interference
True Range:
- 2 RF chips, every with its personal antenna (primarily two receivers on one board)
- Each antennas are continually listening and evaluating alerts, the cleaner sign is chosen in actual time
- Affords higher vary and reliability than antenna range, however comes at the price of larger value and energy consumption
The best way to Inform the Distinction
Each antenna range and true range receivers have two antennas. The distinction is within the {hardware}:
- Antenna Range → 1 RF chain
- True Range → 2 RF chains
For those who examine the board intently, true range receivers may have two unbiased RF receiver chains, whereas antenna range receivers solely have one.
Gemini Mode
In case your ExpressLRS transmitter has two antennas, it’s a superb indication that it helps Gemini Mode. Transmitters with just one antenna are restricted to Fundamental Mode (and variety).
Gemini Mode makes use of two transmitters, every with its personal antenna, to ship the identical knowledge packet on barely totally different frequencies (e.g. ~40 MHz aside on 2.4GHz, or ~13 MHz aside on 900MHz). A real range receiver can choose up these two alerts independently, successfully creating two separate radio hyperlinks. If one hyperlink experiences interference or sign loss, the opposite can take over — considerably enhancing hyperlink high quality and reliability.
I’ve written a full breakdown how ExpressLRS Gemini Mode works: https://oscarliang.com/expresslrs-gemini/
Be aware: Gemini Mode solely works with true range receivers. For those who’re utilizing a single-antenna receiver, or one which solely helps antenna range, it is going to default again to Fundamental Mode.
Gemini Xrossband (Gem-X)
Gemini Xrossband, or Gem-X, takes Gemini Mode one step additional. As an alternative of transmitting two equivalent packets on the identical band, it sends them concurrently on each 2.4GHz and 900MHz.
This requires:
- A dual-band transmitter that helps Gem-X
- A dual-band receiver with Gem-X help
Due to this, Gem-X setups are often the most costly ExpressLRS possibility. However they provide most:
- Vary
- Redundancy
- Resistance to interference
- General hyperlink high quality and reliability
Examples of appropriate {hardware} embody the Radiomaster GX12 radio and the BetaFPV SuperX Nano Receiver.
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Antenna Sorts
Most ExpressLRS receivers use an IPEX MHF1 connector (also called U.FL) for attaching exterior antennas. Nevertheless, you’ll additionally discover receivers with onboard antennas, reminiscent of ceramic tower antennas and flat antennas.
- Onboard antennas – Glorious for compact builds and short-range flying. They save weight and house however sacrifice efficiency.
- Exterior antennas – Advisable for higher vary and reliability.
Receiver Anatomy
RF Chip
The RF chip is without doubt one of the most necessary parts of a receiver. It determines what frequencies, packet charges, and modulation modes the receiver helps.
Frequent chips are:
- SX127X (e.g., SX1276) → Helps 900MHz
- SX128X (e.g., SX1281) → Helps 2.4GHz
- LR1121 → Helps each 900MHz and a pair of.4GHz
Amongst these, the LR1121 is probably the most highly effective, supporting dual-band operation together with extra modulation modes and packet charges.
 BetaFPV ELRS Lite 2.4GHz Receiver with SX-1281 Chip |
 BetaFPV SuperX Mono Receiver with LR1121 Chip (Helps each 900MHz and a pair of.4GHz) |
 Radiomaster RP4DT 2.4GHz Receiver with SX1281 Chip |
 BetaFPV SuperX Nano Receiver with LR1121 Chip (Helps each 900MHz and a pair of.4GHz) |
Right here’s a diagram displaying what frequencies, packet charges and modulations every chipset help.
PA and LNA
PA (Energy Amplifier) and LNA (Low-Noise Amplifier) are parts that enhance the efficiency of the receiver which might be necessary for vary.
- PA can increase telemetry sign hyperlink as telemetry requires the receiver to transmit sign again to the radio.
- The LNA will increase the sensitivity of the receiver and provides you higher vary and hyperlink stability.
Be aware that some compact or funds receivers don’t have PA and LNA to avoid wasting house and price.
TCXO
TCXO (Temperature Compensated Crystal Oscillator) is a kind of oscillator that gives a much more steady frequency with a a lot wider temperature vary. That is necessary as a result of when parts warmth up or quiet down, it may possibly trigger frequency shift within the oscillator, and if that frequency shift is exterior of a sure margin, your receiver will lose reference to the transmitter. So, having a receiver with a TCXO will guarantee optimum efficiency and reliability.
Processor
For the typical consumer, you don’t really want to know the processor (or MCU) however is price mentioning. Frequent processors in ExpressLRS receivers embody:
Built-in Receiver in FC
Some flight controllers have an built-in ExpressLRS receiver on the identical board to simplify setup and cut back weight. That is particularly frequent in tiny whoop FC boards. For max weight financial savings, the onboard antenna is typically only a easy copper wire soldered on to the board. instance can be the BetaFPV Matrix 5in1: https://oscarliang.com/betafpv-air-5in1-f4-1s-5a-fc/
FC with Exterior Receiver vs FC with Onboard Receiver
PWM Receivers
Some ExpressLRS receivers include PWM outputs (servo header pins). These are particularly helpful for wings or conventional RC fashions with out flight controllers, the place it is advisable plug in servos and ESC on to the receiver.
For multirotors, nonetheless, PWM receivers aren’t generally used — it’s a lot simpler and extra environment friendly to attach a receiver to the flight controller by way of a serial port (UART).
Some PWM receiver choices:
Compatibility
| 2.4Ghz Single Antenna TX | 2.4Ghz Gemini TX | 900Mhz Single Antenna TX | 900Mhz Gemini TX | Twin Band Single Antenna TX | Twin Band Gem-X TX | |
|---|---|---|---|---|---|---|
| 2.4Ghz Single Antenna + Antenna Range RX | Fundamental | Fundamental | X | X | Fundamental | Fundamental |
| 2.4Ghz True Range RX | Fundamental, Range | Fundamental, Range, Gemini | X | X | Fundamental, Range | Fundamental, Range, Gemini |
| 900Mhz Single Antenna + Antenna Range RX | X | X | Fundamental | Fundamental | Fundamental | Fundamental |
| 900Mhz True Range RX | X | X | Fundamental, Range | Fundamental, Range, Gemini | Fundamental, Range | Fundamental, Range, Gemini |
| Twin Band Single Antenna RX | Fundamental | Fundamental | Fundamental | Fundamental | Fundamental | Fundamental |
| Twin Band True Range RX | Fundamental, Range | Fundamental, Range, Gemini | Fundamental, Range | Fundamental, Range, Gemini | Fundamental, Range | Fundamental, Range, Gemini, Gem-X |
RX
2.4Ghz Single Antenna RX
2.4Ghz Antenna Range RX
2.4Ghz True Range RX
900Mhz Single Antenna RX
900Mhz Antenna Range RX
900Mhz True Range RX
Twin Band Single Antenna RX
Twin Band Antenna Range RX
Twin Band True Range RX
TX
2.4Ghz Single Antenna TX
2.4Ghz Gemini TX
900Mhz Single Antenna TX
900Mhz Gemini TX
Twin-band Single Antenna TX
Twin-band Gem-X TX
The best way to Change Between Antenna Modes
For those who’re utilizing a Gemini-capable module (one with two antennas), such because the Nomad module or Radiomaster GX12 radio, you may change antenna modes utilizing the ExpressLRS LUA script. In case your transmitter solely has one antenna, you don’t want to fret about antenna modes, it is going to function in Fundamental Mode by default, with no switching required.
- Fundamental Mode: Beneath Antenna Mode, choose Ant1, Ant2 or Change (robotically alternates between antennas).
- Gemini Mode: Beneath Antenna Mode, swap to Gemini.
- Gem-X Mode: choose Gemini below Antenna Mode, and select a packet fee prefixed with “X” (e.g. X150).
In case your transmitter is twin band, you too can select which frequency to transmit on within the packet fee choices: Low band = 868/915Mhz, 2.4G = 2.4GHz.
Essential: In case your transmitter helps Gemini however you’re utilizing it with a single-antenna receiver, you need to choose one of many antenna in Antenna Mode (e.g. ANT1). Don’t allow Gemini, for the reason that receiver can solely sync to at least one transmitter antenna — the second antenna would merely act as interference.
For extra particulars, take a look at my full information on antenna modes: https://oscarliang.com/expresslrs-gemini/#How-to-Allow-Gemini-Mode
Conclusion: The best way to Select ExpressLRS Receivers
For five-inch quads and smaller, a 2.4GHz single-antenna receiver in Fundamental Mode is greater than sufficient for many freestyle and indoor pilots. In order for you further reliability for longer vary flights, think about upgrading to a range receiver and mount the antennas in numerous places on the drone to scale back blind spots.
For 7-inch or bigger long-range rigs, many pilots favor 900MHz, however as I discussed earlier, 2.4GHz is commonly greater than ample. For those who already personal a 2.4GHz transmitter, I like to recommend making an attempt that first. In my view, 2.4GHz is just extra versatile. For those who actually wish to discover 900MHz, then a dual-band transmitter may be the smarter selection for flexibility.
For ultra-long vary, flying in interference-heavy areas, or going behind obstacles, think about Gemini Mode and even Gemini Xrossband (Gem-X). The selection will depend on your wants and funds. Take into accout: Gemini doesn’t magically enhance most vary — physics nonetheless limits how far a frequency can journey. What Gemini does present is best resistance to interference and redundancy for a extra strong hyperlink.
For those who’re shopping for a brand new transmitter module, think about a dual-band possibility that helps Gem-X. This fashion, you’ll be appropriate with just about all ExpressLRS receivers in the marketplace and be extra future-proof. Relating to receivers, although, the only option relies upon solely in your flying model and necessities.