--- title: "OpenRX shows exactly what a 10 mm antenna choice costs in range" locale: "en" url: "https://irz.fr/en/articles/openrx-size-antenna-range-en" markdown_url: "https://irz.fr/en/articles/openrx-size-antenna-range-en.md" category: "tech" tags: ["ExpressLRS", "OpenRX", "radio", "open hardware", "FPV"] published_at: "2026-08-23T18:05:00.000Z" author: "Léa Perrin" translation: "https://irz.fr/fr/articles/openrx-antenne-taille-portee-fr.md" --- # OpenRX shows exactly what a 10 mm antenna choice costs in range Four receivers share the same ExpressLRS core, then add an external antenna, dual-band RF and a second radio. A 5.3 km test measures what each compromise buys. OpenRX could easily be introduced with the most spectacular number available, since some ExpressLRS long-range demonstrations have gone beyond one hundred kilometres; **by contrast**, this receiver family is more useful when read as a set of hardware compromises rather than a distance trophy. The four boards share nearly the same core and then progressively remove or add the things that make a radio link robust. The smallest is roughly **10 × 10.5 mm** with its 2.4 GHz antenna directly on the PCB; the largest approaches **17 × 15.7 mm**, carries two LR1121 radios and requires two external antennas.[2](https://github.com/OpenDrone-hw/OpenRX)[3](https://opendrone.be/products/openrx) OpenDrone put all four on the same logger and rode a little over five kilometres away from the transmitter. Across that route, measured link uptime was **55% for Lite, 80% for Lite-UFL, 95% for Mono and 99% for Gemini**.[1](https://opendrone.be/newsletter/openrx-range-test) Range stops being abstract when it can be read in PCB millimetres, connectors, antennas and a second RF chain. ## Same core All four OpenRX variants use an ESP32-C3, a 3.3 V supply and ExpressLRS firmware. Their PCBs have six layers, while KiCad files, schematics, BOMs and manufacturing data are published under CERN-OHL-S; each variant also carries OSHWA certification.[2](https://github.com/OpenDrone-hw/OpenRX)[3](https://opendrone.be/products/openrx) That makes the family unusually useful as a near-controlled comparison, because the processor and software stack remain common while most of the visible change happens in the radio hardware. > **Four levels** > - Lite: SX1281, 2.4 GHz, on-board ceramic antenna: 10.05 × 10.55 mm > - Lite-UFL: same radio, connector for an external antenna: 10.05 × 10.55 mm > - Mono: LR1121, 2.4 GHz + sub-GHz, RF front-end: 10.05 × 16.35 mm > - Gemini: two LR1121 radios, two RF chains and two antennas: 17.05 × 15.75 mm > Dimensions and architecture from the current OpenRX repository. The three smaller boards grew by about 1 mm after the physically validated fabrication set. Lite and Lite-UFL use the same SX1281 at 2.4 GHz, but their link antennas differ: Lite carries a small ceramic antenna on the PCB, whereas Lite-UFL exposes a U.FL connector for an external antenna.[2](https://github.com/OpenDrone-hw/OpenRX) Mono changes more of the equation by moving to one LR1121 for 2.4 GHz and sub-GHz operation, with additional PA/LNA, RF switching, balun and filtering, while Gemini duplicates that approach around **two independent LR1121 radios**.[2](https://github.com/OpenDrone-hw/OpenRX) ## Tiny antenna Lite's integrated antenna has an obvious benefit: nothing sticks out, no coax needs to be routed, and there is no external antenna lead to tear away in a crash.[3](https://opendrone.be/products/openrx) On a very small craft, removing a few centimetres of wire may matter more than winning a distance contest. OpenDrone's range test shows **the cost of** that compactness: all four receivers travelled together in one test box while the logger recorded link quality, RSSI, SNR and GPS position every second.[1](https://opendrone.be/newsletter/openrx-range-test) Lite was the first board to lose the connection entirely, at **2.89 km**, when a hill moved between receiver and transmitter. OpenDrone also estimates that the trees cost roughly **35 dB** in that test.[1](https://opendrone.be/newsletter/openrx-range-test) > Illustration: The four OpenRX Lite, Lite-UFL, Mono and Gemini boards wired to one logger. All four variants share one test fixture. Their digital core stays similar; antenna, radio IC and diversity become the main visible variables. Credit: [OpenDrone / Incutec](https://opendrone.be/newsletter/openrx-range-test). Lite-UFL already performs much better over the complete ride, with **80%** uptime against Lite's 55%.[1](https://opendrone.be/newsletter/openrx-range-test) Those figures cannot establish universal “U.FL superiority,” because antenna placement, orientation, surroundings and installation all change radio performance; **in this shared setup**, however, moving the link antenna away from the PCB bought substantial margin. ## Two radios Mono and Gemini buy another kind of margin. The LR1121 can operate around both 2.4 GHz and sub-GHz frequencies, while Gemini carries two chips and two antenna paths for ExpressLRS Gemini Xrossband.[2](https://github.com/OpenDrone-hw/OpenRX)[4](https://www.expresslrs.org/software/gemini/) In that mode, one RF path operates in sub-GHz while the second operates at 2.4 GHz. ExpressLRS explicitly says this should not be read as a mathematical range multiplier because sensitivity for the chosen RF mode remains the same; the benefit is maintaining **higher link quality** when interference or obstruction affects the two paths differently.[4](https://www.expresslrs.org/software/gemini/) The ride shows the same pattern, with OpenDrone recording 95% uptime for Mono and **99% for Gemini**, whose longest outage across the route lasted three seconds.[1](https://opendrone.be/newsletter/openrx-range-test) The price is visible immediately on the PCB, where Gemini becomes the largest board in the family, doubles the LR1121 and associated RF front-end, exposes two U.FL connectors and requires two correctly installed antennas.[2](https://github.com/OpenDrone-hw/OpenRX) **In exchange for** better continuity, the design spends more area, components, routing, antennas and power. ## Below noise The most surprising result concerns something other than the farthest point: on the outbound ride, OpenDrone reports that **49% of Gemini packets and 73% of Lite packets arrived with negative SNR**, meaning the wanted signal sat below the measured noise level in the channel.[1](https://opendrone.be/newsletter/openrx-range-test) > Illustration: OpenRX test SNR chart showing many received packets below zero dB. Many packets remain decodable with negative SNR. A large part of the margin comes from modulation and processing rather than transmitter power or antenna size alone. Credit: [OpenDrone / Incutec](https://opendrone.be/newsletter/openrx-range-test). This is where the LoRa modulation used by part of the ExpressLRS mode set matters. Chirp spread spectrum spreads information across a known sweep, allowing the receiver to correlate against that structure and pull data out of noise. OpenDrone estimates about **24 dB of processing gain** in its explanation,[1](https://opendrone.be/newsletter/openrx-range-test) while Hackaday describes the same mechanism through inverse chirp multiplication followed by an FFT.[6](https://hackaday.com/2026/08/22/open-source-expresslrs-receiver-reaches-for-range/) The trade-off remains, and ExpressLRS's own signal tables make it measurable: at 2.4 GHz, for example, 50 Hz LoRa is published at -115 dBm whereas 500 Hz LoRa is listed at -105 dBm,[5](https://www.expresslrs.org/info/signal-health/) so a higher packet rate comes with less margin for weak signals. > **Range has several prices** > - integrated = compact; external = freer placement: Antenna > - 2.4 GHz = smaller antenna; sub-GHz = different propagation behaviour: Frequency > - more packets per second generally reduce LoRa sensitivity: Packet rate > - two radios and two bands improve continuity but enlarge the hardware: Diversity > ExpressLRS itself says Gemini primarily improves link quality, not automatic maximum-distance multiplication. ## Not a record The **5,307 m** figure is useful only if it is not turned into a product rating.[1](https://opendrone.be/newsletter/openrx-range-test) It comes from one route, with a transmitter positioned on a tower, four receivers grouped in one test fixture and real terrain obstacles along the way. Different geography, antennas or radio settings would generate another curve. There is a second limitation for anyone trying to reproduce the result literally. The OpenRX repository says the physically validated board set was ordered on **June 10, 2026**, whereas an August 5 revision changed the clock supply, enlarged pads and grew the Lite, Lite-UFL and Mono outlines by about 1 mm. Those current layouts had not yet been fabricated when the repository status was written.[2](https://github.com/OpenDrone-hw/OpenRX) OpenDrone still marks the receivers **alpha / coming soon** rather than mature retail hardware.[3](https://opendrone.be/products/openrx) Publishing every file makes the design auditable, while the latest Git revision still remains distinct from the board revision that actually went through the field test. That is exactly why OpenRX is more useful than a distance record: the repository lets us follow each trade, from removing the antenna cable to moving the antenna off-board, adding another band and finally duplicating the radio itself. “How far does ExpressLRS go?” becomes almost the least interesting question **relative to** what OpenRX can actually expose about hardware design: **how many millimetres, components and antennas are we willing to spend so that the link disappears less often?** ## References 1. [OpenDrone, OpenRX Video Release — range test](https://opendrone.be/newsletter/openrx-range-test) 2. [OpenDrone-hw, OpenRX repository](https://github.com/OpenDrone-hw/OpenRX) 3. [OpenDrone, OpenRX product page](https://opendrone.be/products/openrx) 4. [ExpressLRS, Gemini](https://www.expresslrs.org/software/gemini/) 5. [ExpressLRS, Signal Health](https://www.expresslrs.org/info/signal-health/) 6. [Hackaday, Open-Source ExpressLRS Receiver Reaches For Range](https://hackaday.com/2026/08/22/open-source-expresslrs-receiver-reaches-for-range/)