LoRaWAN packet received at record distance of 702 km
thethingsnetwork.org
thethingsnetwork.org
Let's say maximum receiver size is roughly 10cm by 10cm, and power consumption can't be over 10 watts, but the "base station" can be as large and powerful as you want.
[edit] cause this is getting some upvotes, here's some thinking I was doing: you can't go through the ground (unless you're at ultra low frequencies and those need antennas measured in tens of kilometers long). So you pretty much have to bounce stuff off the atmosphere, right? When you see stuff like this [0], with thousands of kilometers of range, I imagine that's what happening. Especially as that's 10MHz, which is 30 meters wavelength, which bounces off the atmosphere pretty well IIRC. The only thing with that is that the powers are incredibly low and the antennas are huge. What if you increased the power but decreased the antenna size, for example a 10cm x 10cm antenna with 10W? 100W? 1kW? Would transmissions across thousands of kilometers still be possible?
There are many propagation modes to choose from. HF frequencies (~3MHz to ~30MHz) will propagate via the skywave mode, bouncing off charged layers in the ionosphere. By using codings with extremely low data rates (JT65, QRSS), amateurs routinely make contacts over thousands of miles on a fraction of a watt. Unfortunately, this mode relies on sunspot activity and we're currently at a minimum in the solar cycle. Frequencies below 3MHz will diffract around obstacles and follow the curvature of earth; unfortunately an efficient antenna at these wavelengths is enormously long, so a small system would have absolutely vast antenna losses. NVIS propatation is usable between about 3 and 8MHz, although you're limited to about 600km in a single hop. Multi-hop propagation is possible, although the path loss increases exponentially. Satellite is the other obvious propagation mode and is surprisingly accessible to amateurs.
Solutions to the Shannon-Hartley equation that involve very wide bandwidths are sadly underexplored by the amateur community, because of an FCC requirement to use the narrowest possible bandwidth and the relatively meagre frequency allocations available to amateur operators. The extraordinarily wide bandwidth of a modern direct-conversion transceiver offers some tantalising possibilities.
The data rates would be very low, but for experimental purposes it's viable. The cool thing is there's a ton of simple circuits you can build on your own that other enthusiasts have put online.
The requirement for a small antenna is hard to accommodate, but a lot of people find creative ways to deploy something with a low profile.
I also think the idea of using drones for microwave links has some potential - haven't seen much on that yet but I'm sure people are doing it.
Low speed data can be and is sent using such transmitters, it is done by phase modulating the carrier. The data can be used to switch electrical appliances on and off.
https://en.wikipedia.org/wiki/Radio_teleswitch
https://en.wikipedia.org/wiki/Droitwich_Transmitting_Station
Droitwich puts out 500kW and reception range is on the order of 1000km.
The catch is, thanks to Shannon of course, bandwidth. WSPR will do something like 1.46 baud. That and the 13 meter long antenna.
https://en.wikipedia.org/wiki/Communication_with_submarines#...
Bandwidth is even worse though (<<1 baud), and don't start on antenna length.
>Instead, one has to find an area with very low ground conductivity (a requirement opposite to usual radio transmitter sites), bury two huge electrodes in the ground at different sites, and then feed lines to them from a station in the middle, in the form of wires on poles. Although other separations are possible, the distance used by the ZEVS transmitter located near Murmansk is 60 kilometers. As the ground conductivity is poor, the current between the electrodes will penetrate deep into the Earth, essentially using a large part of the globe as an antenna. The antenna length in Republic, Michigan, was approximately 52 kilometers (32 mi).
> "This article needs additional citations for verification."
Mud modulation.
Basically, while drilling, mud is pumped down the drill string and back out for cooling and cleaning purposes.
Some genius at one of the major oil drilling companies (maybe Schlumberger?) came up with the crazy idea of modulating the mud pressure to transmit information into the depths of the earth. You can control the drill bit speed, angle of drilling, and monitor all sorts of diagnostics over a mud-based communication channel. The bandwidth is decent (think: dial-up), especially when the drilling tools use an efficient modulation scheme.
It's amazing stuff to see first-hand.
wait until you see the NSA mud-pipe-tap.
Very clever...
I regularly see APRS packets of 120mi+, although probably at a lot more power. The current record seems to be near ~2,000 mile[1] bounced from the ISS.
[1] - http://qrznow.com/new-iss-packet-distance-record-claimed/
We were transmitting at 3 watt using a small Yaesu hand-held connected to a micro-controller.
WSPRNet[0] is a network of WSPR transceivers that use milliwatts to communicate across the world. It's just.... very slow.
Edit: And this is very frequency dependent.
> The distance was 3,089 kilometers (approximately 1,915 miles)
I can't recall if Ubiquiti ever had any 900 MHz radios or not but they have plenty in the 2.4/5 GHz (unlicensed) bands as well as the 3.65 GHz (licensed) bands that would probably serve your needs for cheap. Unfortunately, the 900 MHz band is getting quite crowded these days, leading to lots of interference and reduced "throughput".
Mimosa is another (younger) company making similar gear that's relatively cheap with good bang for the buck.
A place I do some work for has several 15-20 mile links (6/11 GHz) pushing ~500 Mbps although those are much more expensive.
As with all VHF and higher data comms what matters most is antenna height and line of sight. I can get 3km fine up on a big hill or lose signal only 300m away from home in other directions.
The longest one with a photograph is 443km (275mi).
The modulation scheme is essentially FM with a twist: high bitrate mode is essentially straight FSK and lower rate modes are FM modulated with sawtooth, which is or is not inverted in each period depending on the transmitted bit. The idea is essentially same as various QRP modes involving painting images on waterfall diagram. (Full gateway nodes receive full band and can track ~50 transmitting nodes at once)