I'm designing a drone(UAV) as a hobbyist, and radio communications is not my strong point. I will be transmitting waypoints from a portable control station and receiving video(a low frame rate is ok). I'm trying to decide what frequency I should use. I want to get a range of about 1 - 2 miles with not a lot of power. Are there power to range benefits from using different frequencies? At the moment I'm thinking about using 2.4Ghz is this suitable for my needs? Thanks!
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$\begingroup$ Wireless house phones and wifi routers use that frequency and do not achieve that range. $\endgroup$– OptionpartyApr 27, 2015 at 22:11
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$\begingroup$ Yes, but they are quite limited on power. If you were to use more power, it would allow for video to be transmitted relatively effectively. $\endgroup$– PearsonArtPhotoApr 27, 2015 at 22:18
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$\begingroup$ Take a look at arrl.org/atv-fast-scan-amateur-television $\endgroup$– PearsonArtPhotoApr 27, 2015 at 22:18
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2$\begingroup$ Can you quantify 'not a lot of power' and 'low framerate' into some hard numbers? Do you have a link budget, will everything be line of sight, what kind of antenna's will you be using? All these factors come in to play as well. 2.4GHz is fine in itself for what you're trying to do. $\endgroup$– captchaApr 27, 2015 at 23:03
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$\begingroup$ The maximum power for the rc would be 300mA at 12V. I would be able to live with 1 FPS @ 720p, though 5 fps is what I'm looking to achieve. It will be a clean line of site, yes. I am thinking about using dipole's antenna, tough I'm not sure if this is suited. My link budget is £120. $\endgroup$– AaronApr 28, 2015 at 10:53
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3 Answers
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The frequency you choose is largely irrelevant with respect to range, at least within the range of frequencies you are likely to choose for this kind of application.
Size limitations (and probably licensing requirements) will probably dictate VHF or UHF, and so you will be using line-of-sight propagation. Regardless what frequency you select, electromagnetic radiation is subject to the same inverse square law. That is, in the absence of obstructions, 2.4 GHz radiation "travels just as far" as that of any other frequency you might reasonably choose for radio communication.
See:
answered Apr 28, 2015 at 14:14
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$\begingroup$ So assuming my calculations are correct I can reach a range of 2.5 Miles (4 KM) . Free Space Path Loss: 107.9 dB , output 18dB, -95 dB sensitivity $\endgroup$– AaronApr 28, 2015 at 16:35
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$\begingroup$ @Aaron assuming isotropic antennas and no other sources of loss or interference, that sounds right. But it's probably overoptimistic: in real life you need some margin in the link budget. And assuming you are using the 2.4 GHz ISM band in a populated area, the noise floor is going to be well above -95 dBm. $\endgroup$ Apr 29, 2015 at 1:03
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$\begingroup$ Heh. I love that phrase: isotropic antenna. Makes me laugh every time. Throw in no other sources of loss or interference and I LOL. Meanwhile, great comment on real life, @Phil.. $\endgroup$– SDsolarSep 9, 2017 at 6:09
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If you mean 2.4Ghz for video, how are you going to control the R/C model? 2.4Ghz spread spectrum is the most common R/C control link. A 2.4Ghz video transmitter would probably swamp your R/C control RX.
I've done a 3.5mi flight with 2.4Ghz control and 5.8Ghz video. That was a 200mW video transmitter, and a "pepperbox" antenna. It's very directional. It has a 160deg beam width, but 60deg beam height. I was also out in the middle of nowhere where the noise floor was really low (and I wouldn't damage anything if I crashed and I knew I could retrieve if I crashed). The flight was pretty much straight and flat. I say all this to say that the environment and antennas matters a lot.
In general you'll have better luck with video on lower frequencies. 900Mhz is about the lowest I have seen folks use for video, antennas get pretty big though. It might be hard to find ready-made gear for anything else. I have seen some compact 1.3Ghz antennas.
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You might be looking for wifibroadcast, a form of low latency digital video broadcasting (motivated by controls of R/C models...)
Prominent features:
- uses Raspberry pi
- uses raw wifi frames, thus does not need association between the receiver and the transmitter
- video is received as long as the receiver is in range, with increasing number of errors as the signal drops (but the connection does not drop sicne there is no connection)
- low latency
- kilometer(s) range is achievable in good conditions
- diversity (reception with two different antennas) can improve reception under low signal/noise/reflections conditions
- unfortunately, wifi hardware does not pass frames with errors, which makes the reception less ideal (lower range) than it could be
