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Why do TBS Crossfire, ELRS etc. not use lower frequencies like 433MHz? If we omit legal regulations and antenna size, are there any drawbacks?

Lower frequencies provide longer communication distances, but they also cut down communication bitrate. If it's because of the bitrate, what minimum bitrate is required for FPV piloting? What is the minimum possible operating frequency?

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Lower frequencies provide longer communication distances.

No, not in general. While the free-space path loss is lower for the same frequency, your antenna needs to be larger. Use a larger antenna at a higher frequency, and you get more effective area. These effects have the same magnitude.

I don't know any of the abbreviations you use, but I guess you want a live video stream, at low latency. Well, it depends on the resolution and image quality you want, but you'll want several hundred kilobits at bit error rates below 10-3, so that basically rules out these bands.

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  • \$\begingroup\$ ELRS stands for Express LRS (haha) - its an open-source hardware-software for drone piloting. TBS is the company that creates the same stuff, but proprietary. I don't want video stream, I want control and telemetry support \$\endgroup\$
    – Secret-guy
    Commented Dec 8, 2023 at 15:31
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    \$\begingroup\$ @Secret-guy You didn't explain probably the most important acronym in your question: what does FPV mean? \$\endgroup\$
    – Hearth
    Commented Dec 8, 2023 at 16:29
  • \$\begingroup\$ First-Person View drones. It's usually about quadcopters that have an onboard camera and the pilot wears "FPV Goggles" and can see the world and flight process from the drone's perspective. These drones use separate RX/TX for video transmission and for control/telemetry. I have analog video transmission already set up (it uses 1.3GHz) and am working on the development of a control transmission \$\endgroup\$
    – Secret-guy
    Commented Dec 8, 2023 at 17:36
  • \$\begingroup\$ If the pilot wears goggles, you will want very low latency. \$\endgroup\$
    – Fredled
    Commented Dec 8, 2023 at 19:53

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