Eli5- How do consumer drones (DJI, etc) broadcast the camera image to your phone from so far away? How come you can control a drone and view the feed like a mile away but I have trouble getting Wi-Fi reception on the other side of condo
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The ones Ive used aren’t wifi or bluetooth, they have a sim card and use mobile data like your phone.
Edit- I have a short range one that uses bluetooth, but it only has a range of like 15 feet.
Drones use radio signals to operate. Similar to how your car radio can get sound or how your TV used to work. Radio waves can travel pretty far, but objects and other radio waves can interfere with them. Wifi uses radio as well, but doesn’t use a strong signal. I mean, you don’t want the whole city to be able to see your network. Also, wifi routers are indoors. So there can be a lot of walls, electrical components, or other things in the way to your TV or phone.
My drone has a 3 mile max distance… in perfect conditions. In reality, I can see about a mile to a mile and half depending on where I am. I did try and fly it outside while I was inside once and the distance was like a quarter mile or less. Two miles is the max I’ve flown it and I was in the country with an OK line of sight. Had I been on top of a hill, then I could have probably flown it the full 3 miles.
There are two important things range of communication depends on when it comes to radio communication frequency and power. Higher frequency means more data but less range, this is why 5 ghz can carry more data than a 2.4 GHz wifi signal. Power increases range but the further your signal travels but the fewer people can use the same signal without interference. Like imagine being in a crowded room the louder people talk the lower the amount of productive conversations but the further away you’ll be able to hear a particular person. Now both wifi and Bluetooth are heavily used and therefore their power is severely limited. However if you use a different frequency band with higher power limits you can greatly increase range
The answer is compression, codecs, and request time.
How do you stream a youtube video on your phone from miles away? It gets compressed. Same with a drone. You’re not really watching the video in its full glory on your phone. You’re watching what is basically a rough sketch of what the video actually looks like. Computers are really good at making those sketches, so it looks fine to you, but it is not what you would see on a nice 4k TV.
Compression can make videos really small, and the exact way the codec that does the compression works can be optimized for things like smoothly playing back a live feed, even when a couple frames get lost in transmission so it looks extra good in that one special use case.
Okay, sure, playback is possible – but YouTube always needs to buffer and sometimes cuts out, what’s stopping that from happening here? When you watch a YouTube video, you are requesting the video from a server, that basically keeps going back to a filing cabinet to get you the next few frames. But that server is handling many requests from many people for many different videos. If communication gets disrupted, the server in this three-step conversation might need you to remind it what you wanted, or it might need to find the right filing cabinet again – making interruptions much more noticeable.
With a drone, there are only two things talking: you and the drone. The drone is sending its video directly, so even if the transmission screws up, it’s not like either end needs to guess what it was supposed to be doing – the very next instant the drone will be back to sending video to you – and the drone probably uses a codec that helps gloss over this when it does happen.
A big factor is line of sight. Walls (especially steel reinforced concrete), wires, plumbing etc. can all attenuate radio signals strongly.
Without obstacles normal 2.4GHz Wifi or Bluetooth can reach ~100m range. With good, directional antennas this can be extended to several kilometres.
The biggest limitation in the 2.4GHz part of the spectrum is the low power limit. Most regulations only allow up to 100mW of transmit power. In other parts of the spectrum you are allowed to transmit with *a lot* more power. Like 25W or even more.
As others have said, lower frequencies (e.g. the 35MHz band used by RC aircraft) tend to propagate better through obstacles and are less affected by water vapour.
Most of the reduction in range in your home WIFI comes from the walls in your house blocking the signal.
A drone, however, has a clear line of sight, which means the signal is reduced a lot less.
There are a few very misguided explanations here already.
ELI5 answer: They are allowed to talk to each other under different rules than your laptop talks to your wifi hotspot.
Short answer: Because they are using frequencies with less interference and more relaxed power rules than what WiFi permits TOGETHER with radio protocol designed for long-range use.
Long answer: While there are some drones that indeed will connect via wifi or bluetooth their range and power will be limited by law. Try Mavic Air via wifi link or via remote control – completely different ranges. The difference is that remote control talks to the drone NOT via wifi, but via its own radio protocol in frequency range _outside_ of wifi frequencies (but very close, which is why most people see 2.4GHz and think it is still wifi).
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Question: Why doesn’t WiFi do the same and give same range?
Answer: WiFi is designed to be cooperative among large number of devices active at any time. WiFi devices have strict limits on how loudly they can talk with each other (to be fair to others) and try to squeeze in a lot of data each time they get a chance to have a word (transmission window) so that your netflix 4k stream has enough data meaning that signal is more complex to understand (and degrades quicker). If everyone who uses wifi around you would do the same nothing would work for anyone.
Look up bps.space on YouTube they have some quite good board designs where they talk about this sort of thing.
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