3 ms·

>> point-to-point over anywhere from 5-20km I think 20km point to point is not to be sniffed at if my back of a napkin calculations are correct (would love som

>> point-to-point over anywhere from 5-20km I think 20km point to point is not to be sniffed at if my back of a napkin calculations are correct (would love someone more knowledgeable to correct!) Firstly on LOS - that’s like 15m+ masts at each end of the link (assuming perfect LOS path with no clutter like trees or buildings). Then on free space path loss you’d be looking to overcome around 100db+ of path loss i think assuming 2.4ghz ISM band and perfect atmospheric conditions. 10dbi / 12 dbd log periodics for 2.4ghz are available off the shelf and are very reasonable to use (not too big, not too much wind loading at 15m elevation, weatherproof etc.) Recieve sensitivity should be around -110dbm maybe? Assuming fairly rural conditions so that you’re not also dealing with a man made noise floor (and also benefitting from a very directional antenna to miss most noise too). You’d need a 1 watt power amplifier minimum, again that’s more or less off the shelf but there’s restrictions globally on use and that may make sourcing harder.

madaxe_again 4y ago
The loss is only one facet of the problem - the round trip time becomes a significant problem, requiring large windows and timeouts and general weirdness - time travelling ARPs, for one - as does the ability of consumer equipment to send a signal your AP can receive. The Wi-Fi antenna in a phone or laptop is not generally very powerful. The limiting factor isn’t the AP, in short. Now, running LTE microcells - that’s a viable option in a desperate environment, and one that can be done with SDR. Only problem is then getting consumer equipment to authenticate with it. This is possible, either with eSims or with cooperation from local regulatory authorities - but not altogether trivial. This is borne off the back of experience - I tried to do long range Wi-Fi, but for a usable experience from consumer gear (a phone), 2.5km was about as far as I could get with a 1 watt amp on a dipole. Got much further with a yagi, but funkiness emerges beyond about 4km on 802.12g. You’d get further on b but your rates will be pants. I would do LTE for this application. My solution where I am is a mast that receives LTE atop a hill and has four yagis doing 802.11g to receiver nodes, which each comprise a repeater with a yagi pointed at the mast, and a dipole omni to get a solid 500m radius around each repeater. I’ve covered 15ha of tortured terrain with Wi-Fi with this - and come to think of it, the highly directional signals could provide hardness against interference and would greatly mitigate interception issues. Oh, and I’d you’re doing yagis, you need real ones, not the fake crap you’ll usually find for sale. The real deal is about 70cm long for 2.4ghz and will have tapered vanes to the point. Commercial models come in a plastic can.
ac29 4y ago
Just to clarify for people reading this comment: This: >10dbi / 12 dbd log periodics for 2.4ghz are available off the shelf [I assume this is actually talking about 12dBi and 10dBd which are equivalent] combined with this: >You’d need a 1 watt power amplifier minimum Is very illegal in the US and probably most other places in the world. There is a hard 1W transmit power limit and a 6dBi antenna gain limit. Fixed point to point links can use higher gain antennas in combination with lower transmit power, but there is no situation in which 1W transmit power + 12dBi gain is legal.
- squarefoot 4y ago
  They're at war and being constantly bombed; I think being legal or not is the least of their concerns.

madaxe_again 4y ago

The loss is only one facet of the problem - the round trip time becomes a significant problem, requiring large windows and timeouts and general weirdness - time travelling ARPs, for one - as does the ability of consumer equipment to send a signal your AP can receive. The Wi-Fi antenna in a phone or laptop is not generally very powerful. The limiting factor isn’t the AP, in short. Now, running LTE microcells - that’s a viable option in a desperate environment, and one that can be done with SDR. Only problem is then getting consumer equipment to authenticate with it. This is possible, either with eSims or with cooperation from local regulatory authorities - but not altogether trivial. This is borne off the back of experience - I tried to do long range Wi-Fi, but for a usable experience from consumer gear (a phone), 2.5km was about as far as I could get with a 1 watt amp on a dipole. Got much further with a yagi, but funkiness emerges beyond about 4km on 802.12g. You’d get further on b but your rates will be pants. I would do LTE for this application. My solution where I am is a mast that receives LTE atop a hill and has four yagis doing 802.11g to receiver nodes, which each comprise a repeater with a yagi pointed at the mast, and a dipole omni to get a solid 500m radius around each repeater. I’ve covered 15ha of tortured terrain with Wi-Fi with this - and come to think of it, the highly directional signals could provide hardness against interference and would greatly mitigate interception issues. Oh, and I’d you’re doing yagis, you need real ones, not the fake crap you’ll usually find for sale. The real deal is about 70cm long for 2.4ghz and will have tapered vanes to the point. Commercial models come in a plastic can.

ac29 4y ago

Just to clarify for people reading this comment: This: >10dbi / 12 dbd log periodics for 2.4ghz are available off the shelf [I assume this is actually talking about 12dBi and 10dBd which are equivalent] combined with this: >You’d need a 1 watt power amplifier minimum Is very illegal in the US and probably most other places in the world. There is a hard 1W transmit power limit and a 6dBi antenna gain limit. Fixed point to point links can use higher gain antennas in combination with lower transmit power, but there is no situation in which 1W transmit power + 12dBi gain is legal.

squarefoot 4y ago
They're at war and being constantly bombed; I think being legal or not is the least of their concerns.