We're still in communication with Voyager 1, which is operating on a grand total of about 20W of RF power; and is currently about 14.5 billion miles away.
At the receiver, you have "minimum detectable signal", MDS, measured in dBm.
At the transmitter, you have power out, measured in dBm. Add transmitting antenna gain, in dB, subtract propagation loss through medium(s), add receiving antenna gain, and if that number is greater than MDS, you win! The Really Great Science in Voyager is the added factor of "coding gain" -- sophisticated error correction codes can give you a many dB adder, at the expense of data rate (nobody cheats Claude Shannon).
Indeed. If you grow up with your most common radio interactions being an FM car radio and a dumbphone, you get the impression it's entirely about range. Then you buy a drone and find out one pine needle shaves 50% off of your signal strength.
iirc the claimed range is around 8km on the one i have, about 5 miles. I have assuredly gone well over 2km with no issues with control or video feed. This was over a straight highway. I routinely fly around a kilometer away, and the only issues i have is if i launch from an extremely dense patch of pine trees, and only at about 800-900 meters, i will lose video (artifacting for a second), but not control. It's never had to RTH.
In case you're curious about city usage, i have a friend that has one he launches from a culdesac in Orange County and can fly in nearly any direction for about 8 minutes* before he hits a geofence, the drone still functions normally. If there is any issues, he can just fly higher.
The newest newest DJI stuff claims even more ridiculous range, 15km+ over open water, for instance.
If i hadn't used it myself, i wouldn't have believed it, it sounds like BS.
* this is 5-7km depending on the tailwind
Is there anything particularly special about the antennae on the spaceship? They must be rigorously aligned to point at Earth, and even a slight knock would spoil everything? Or is it more resilient than that?
If you threw a beach ball from the distance of voyager straight to earth it would eventually make it here.
At $865 million[1] and 14.5B miles that about 0.034 Euros/Km. 1/20 of what he did in 2005.
1: https://voyager.jpl.nasa.gov/frequently-asked-questions/fact...
In terms of size usually guard interval < slot size < inter-frame space. If propagation exceeds guard interval AND have a channel with lots of echo any communication will be difficult. If propagation exceeds slot timing then coordination between more than 2 devices will be different (high retries/low throughput). If propagation exceeds interframe spacing a two-way wifi connection will not be possible as both stations will think every frame timed out waiting for an ACK.
More info here: https://en.wikipedia.org/wiki/Guard_interval https://en.wikipedia.org/wiki/Distributed_coordination_funct... https://en.wikipedia.org/wiki/Short_Interframe_Space
For really long range propagation on earth, reflections on atmospheric layers are the dominant factor (as there is no line of sights due to the curvature of the planetary surface).
See https://www.sciencedirect.com/topics/engineering/atmospheric... for some nice graphs.
Now this might be significant enough in directional waves with a huge constant multiplier (like a 'ideal' laser with no divergence). Someone can probably give insight on it here.
1. https://www.researchgate.net/publication/270512069_Propagati...
Certainly the author picked a beautiful region to do that kind of outdoor experiment in.
My impression though is that recent advancements in wifi have all been focused on getting high bandwidth at very short range, like same room line-of-sight, so I wouldn't assume there'd be much to be gained over b/g/n range performance in trying an ac- or 6-based system.
But with 440mhz i've transmitted data over 100 miles with full decode, from my driveway in a forest with a 6 element yagi. And a couple of years ago the first trans-atlantic 440 (UHF) transmission ever was accomplished.
The main issue with consumer wifi is that it's attenuated by water, and by nature, nature is full of water. That's why UBNT switched to 12ghz or 24ghz for their long range "airfiber" stuff, and hacker hams try and find 902MHZ band capable equipment, as 900mhz can "punch through" more vegetation than 2.4 or 5.8ghz.
I don't mean to be argumentative, but I wonder what the ugliest 43.33km line of sight environment one could find would be? I imagine it's quite a good proxy for beauty, the maximum distance you can see.
Or maybe somewhere like North Korea.
https://en.wikipedia.org/wiki/File:Fillmore_03_Hwy_33.jpg
Flat. Flatter. Flattest. With virtually zero change in elevation there is very little to see but pavement and sky.
This is on purpose: the idea is to make the common WiFi (and Bluetooth) bands short range on purpose, so that many people within a city block can have local WiFi or local Bluetooth without interfering with each other.
So 2.4GHz over a long distance kinda goes against the design of WiFi / Bluetooth.
This isnt really true to any significant degree that matters, unless you are literally under water.
Rain fade is a thing, but is really only meaningful above 10GHz.
edit: I should note, its not that water droplets dont attenuate radio signals, its just that losses on a typical radio path are already huge in perfectly clear weather - you might lose 99.99999999% (100dB) or more of your signal strength between transmitter and receiver anyways.
PSA: we need more HAMs out there! Check out https://hamstudy.org and get your license https://hamstudy.org/sessions/remote
The hash is just a reason for people to complain about them. As shipped from the factory, they're below the minimum hash levels required. Now, if you connect them to a cheap RF amplifier, you might run afoul of your license's rules about hashing up the harmonics.
Personally i prefer quansheng, as their speakers are louder, but i've never had an issue with a baofeng, especially with an external speaker/mic/antenna.
for posterity, i am extremely tired, and i welcome all elucidations and corrections, because i'm probably misremembering something, here.
Very simplified, the signal is carried within a "fresnell zone", which s basically a 3d ellipse, that is relatively wide in the middle, and you'd have to cover a lot of that area, to block the signal... definitely more than a bird can do. https://en.wikipedia.org/wiki/Fresnel_zone#Clearance_calcula...
...unless the bird is standing infront of the transmitter/receiver.. then yes.
This is a neat exercise in antenna design. They've built high gain directional antennas and minimized transmission line losses. The 15 dBi antennas aren't even that remarkable; you can buy 30+ dBi wifi antennas.
My first 'better than dial-up' internet connection was a 2.4 GHz wifi service across 7 miles. On my end was a roof mounted aluminum parabolic grid antenna. It worked rather well and sometimes I wish I still had it.
Of course you’d have a little problem with the battery :-)
Of course, the VTX is usually a different matter..
[0]https://www.expresslrs.org [1]https://www.expresslrs.org/2.0/info/long-range/
https://flylib.com/books/en/2.434.1/hack_83_make_a_deep_dish...
Now-a-days, mikrotik or ubnt make doodads you can replace the LNB with that instead provides some wifi band, with PoE, so two of those up on a tower means you have active repeating, and you can probably push that solution out a lot further than 43km.
For the record, i put a USB wifi stick inside of a pirouette cookie can and it was a phenomenal "war driving" antenna. I use folded-dipole-fed yagi antennas now for doing wifi surveys, but in a pinch 802.11B 1000mW+ wifi cards are stacked up in a filing cabinet...
[0]https://web.archive.org/web/20050201000000*/https://www.qsl....
https://en.wikipedia.org/wiki/Cantenna
width or diameter is a criticalproperty:
https://www.everythingrf.com/tech-resources/waveguides-sizes
https://web.archive.org/web/20161029045619/http://www.pwmn.n...
have fun, and dont cut yourself, they do work well when used at both ends of the line.
https://web.archive.org/web/20071012133113/http://www.saunal...
There's also this misconception that speed is the only thing that matters, so "higher speed = better connection" and the vast majority of consumer-grade tools only ever test for this. This is where it will mislead you, as an unstable connection with short bursts of high speed will appear "better" (despite being fragile and completely unusable for anything real-time) than a slower but more reliable connection. In-browser speed tests are extremely bad for this because all the buffering & various layers could even fool the test code itself, making it believe it's getting a steady stream while in reality it's getting merely short bursts of data (in between tons of underlying TCP retransmissions). Iperf & ping are the tools of choice if you actually want to look into it - they are closer to the metal and will give you faster feedback (you will be able to actually see the dropouts due to packet loss).
See https://en.wikipedia.org/wiki/Free-space_optical_communicati....
Broadcast packets with the SSID aren't too difficult to get. You only need to get one.
Fun regardless, but I'm curious for more info.
A bit higher quality point-to-point can be obtained with a bit of specialized equipment, Mikrotik has a bunch: https://mikrotik.com/product/MTAD-5G-30D3-PA for example, can go 40+ km.
https://www.openstreetmap.org/directions?engine=fossgis_osrm...
https://web.archive.org/web/20061205205844/http://www.aftenp...
Perhaps given the limitations of 802.11 it means something but in theory it's meh.
