WEBVTT NOTE Control Link Spectrum and Why Links Fail 1 00:00:00.000 --> 00:00:04.085 Where your aircraft lives in the spectrum. 2 00:00:04.085 --> 00:00:24.021 Almost every consumer and prosumer sUAS uses unlicensed Part 15 spectrum: Band, 2.4 GHz (2400 to 2483.5 MHz); Typical use, command and control, sometimes video; Character, longer range, far more congested. 3 00:00:24.021 --> 00:00:37.442 Band, 5.8 GHz (5725 to 5850 MHz); Typical use, video downlink, sometimes C2; Character, more spectrum, shorter range, more easily blocked. 4 00:00:37.442 --> 00:00:58.156 Band, 900 MHz; Typical use, long-range C2 on some platforms; Character, best propagation, least bandwidth. Two things follow from "Part 15", and both matter operationally: You have no protection from interference. 5 00:00:58.156 --> 00:01:14.105 Part 15 devices must accept interference from anyone. Your control link shares 2.4 GHz with every Wi-Fi access point, Bluetooth device, and microwave oven in range. 6 00:01:14.105 --> 00:01:26.359 You need no licence, and your amateur licence buys you nothing here. The equipment is certified; you operate it as a consumer. 7 00:01:26.359 --> 00:01:38.319 Why links fail. Every lost-link event you will experience is one of five things, and the antennas and propagation lessons already explain each. 1. Distance. 8 00:01:38.319 --> 00:01:52.042 Free-space path loss goes as the square of distance and the square of frequency. Doubling the range costs 6 dB; moving from 2.4 to 5.8 GHz costs about 7.7 dB at the same distance. 9 00:01:52.042 --> 00:02:08.448 This is why 5.8 GHz video drops out well before 2.4 GHz control does, by design, so you lose the picture before you lose the aircraft. 2. Obstruction. At these frequencies, propagation is essentially line-of-sight. 10 00:02:08.448 --> 00:02:24.087 A building, a hill, or a stand of trees between you and the aircraft attenuates severely. Your own body counts, turning your back on the aircraft while holding the controller measurably reduces signal. 3. 11 00:02:24.087 --> 00:02:33.594 Fresnel zone intrusion. Even a clear visual line of sight is not enough: the first Fresnel zone must be substantially clear. 12 00:02:33.594 --> 00:02:50.460 Flying low over terrain that rises between you and the aircraft degrades the link while the aircraft remains plainly visible. This is the same effect as the ground gain and take-off angle material in the antennas module. 13 00:02:50.460 --> 00:02:58.740 4. Multipath. Reflections from buildings, water, and vehicles arrive delayed and can cancel the direct path. 14 00:02:58.740 --> 00:03:09.779 Near large flat surfaces the link can be worse at 50 m than at 200 m, which feels like equipment failure and is not. 5. Co-channel interference. 15 00:03:09.779 --> 00:03:20.359 A crowded 2.4 GHz environment, an event, an industrial site, an apartment block, raises the noise floor until your link budget disappears. 16 00:03:20.359 --> 00:03:29.403 This is measurable before you fly: point the SDR from the lab track at 2.4 GHz and look at the occupancy. Antenna behaviour. 17 00:03:29.403 --> 00:03:40.781 Controller antennas are usually simple dipoles or patches, and their pattern matters more than people expect. A dipole radiates broadside, not off its ends. 18 00:03:40.781 --> 00:03:51.940 Pointing the controller's antenna tips directly at the aircraft puts it in the pattern null, the worst possible orientation, and the most common mistake. 19 00:03:51.940 --> 00:04:01.860 Keep the antennas broadside to the aircraft: perpendicular to the line between you and it, and roughly vertical for a hovering aircraft. 20 00:04:01.860 --> 00:04:15.790 A directional patch or helical adds gain and range at the cost of a narrow beam you must keep pointed. Useful for long linear missions, actively harmful if the aircraft manoeuvres around you. 21 00:04:15.790 --> 00:04:27.825 Height helps disproportionately. Raising the controller a metre or two, or standing on a vehicle, often recovers a marginal link, because it clears the Fresnel zone. 22 00:04:27.825 --> 00:04:40.759 Lost link. section 107.21, In an in-flight emergency, the remote pilot in command may deviate from any rule of this part to the extent necessary to meet that emergency. 23 00:04:40.759 --> 00:04:49.613 A deviation must be reported to the Administrator on request. Lost link is the emergency Part 107 most anticipates. 24 00:04:49.613 --> 00:05:08.552 The aircraft's programmed behaviour, usually return-to-home, executes without you, so the pre-flight configuration is the emergency procedure: Verify the return-to-home altitude clears every obstacle between the operating area and the home point. 25 00:05:08.552 --> 00:05:25.259 An RTH altitude below a nearby tree line is a scripted collision. Confirm the home point is set where you actually are, especially after moving the control station. Know the failsafe behaviour: hover, land, or return. 26 00:05:25.259 --> 00:05:30.417 They fail very differently over water, over a road, or over people. 27 00:05:30.417 --> 00:05:45.195 What the amateur bands can and cannot do. Amateur allocations overlap the drone bands, 2.4 GHz is the 13 cm amateur band, and 5.8 GHz is within the 5 cm band, so the question comes up constantly. 28 00:05:45.195 --> 00:05:47.999 The answer is narrower than it looks. 29 00:05:47.999 --> 00:06:03.307 What an amateur licence permits: operating amateur-licensed equipment, including FPV video links designed for Part 97, under amateur rules, with the higher power limits and the antenna gain those allow. 30 00:06:03.307 --> 00:06:15.054 What it does not permit:. Anything with a pecuniary interest. section 97.113 prohibits communications in which you or your employer have a financial stake. 31 00:06:15.054 --> 00:06:26.270 A commercial Part 107 flight cannot use an amateur-band link, ever. This is the single most important point in this lesson. Encrypted control links. 32 00:06:26.270 --> 00:06:39.684 Obscuring the meaning of a transmission is prohibited under Part 97, and most commercial C2 protocols are encrypted. Operating a Part 15 certified radio at amateur power levels. 33 00:06:39.684 --> 00:06:51.203 Modifying certified equipment moves it out of its certification, and a certified device is not an amateur transmitter merely because you hold a licence. 34 00:06:51.203 --> 00:07:04.617 Practically: amateur-band FPV is a legitimate hobby activity for recreational flight under Part 97 rules. For Part 107 work, use the Part 15 equipment the aircraft shipped with. 35 00:07:04.617 --> 00:07:21.125 Check yourself. Your video drops out at 400 m but control is solid. Broken, or expected? You are flying over a large car park and the link is worse close in than further out. Why? 36 00:07:21.125 --> 00:07:31.547 You are being paid to inspect a roof and want to use your 2.4 GHz amateur FPV gear for a better picture. May you? 37 00:07:37.547 --> 00:07:54.191 Expected. 5.8 GHz video has roughly 7.7 dB more path loss than the 2.4 GHz control link at the same distance, so the picture is designed to fail before the aircraft does. Multipath. 38 00:07:54.191 --> 00:08:05.777 Reflections from the flat surface and the vehicles arrive delayed and can cancel the direct path at particular geometries. No. 39 00:08:05.777 --> 00:08:19.387 section 97.113 prohibits communications in which you or your employer have a pecuniary interest. A paid flight rules out the amateur bands entirely.