91–100 of 168 posts
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Just use Unifi Airfiber for 6 miles at gigabit speeds. If you're relying on line of sight then 2.4GHz is nonsense. And if you don't have line of sight then no you're not getting 6 miles
Is UniFi Air fiber extremely low power and cheap to produce?
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Correct. The LoRa configurations mentioned which offer 100× the speed of Meshtastic/Core operate at 800 kHz and 1.6 MHz bandwidth, which are permitted by the FCC in 15.247. As far as I know there's not actually anything particular to 2.4 GHz allowing higher throughput for LoRa than that the corresponding Semtech chip happens to support wider bandwidths. (I.e. no legal barrier.) The tradeoff is less range due to lower…
What issues does it create for others to use too narrow of a bandwidth? Why “should” the FCC care if someone is only using a small portion of the spectrum that would otherwise be fine fr them to use? Thanks for educating us!
The legal power limit in these bands is 1 W. If you spread that out over 500 kHz, that signal is weaker than background noise at any given frequency for anyone more than about a city block away. (Give or take many factors.)
But, if you compress that 1 W into, say, 12.5 kHz (typical for FM voice), your signal is now detectable (and will interfere with other, possibly licensed, users) at over 6 times the distance.
There are probably other factors. For example, it's not legally sufficient to simply reduce your power by a corresponding factor. I suspect it may simply be the FCC's goal to reduce conflict between users by mandating spread-spectrum technologies for unlicensed use.
Note also that 47 CFR 15.247(e) [1] gives a spectral power limit which corresponds approximately with the 1 W max / 500 kHz min specified in (b)(3) and (a)(2).
Final side note – https://docs.fcc.gov/public/attachments/FCC-02-151A1.pdf is interesting reading as to how the current form of 15.247 came to be. Specifically it changed the rule from specifically DSSS to digital modulation generally, which in turn allowed the transition from 802.11b (DSSS) to 802.11g (OFDM) on 2.4 GHz.
[1] https://www.ecfr.gov/current/title-47/part-15/section-15.247...
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Correct. The LoRa configurations mentioned which offer 100× the speed of Meshtastic/Core operate at 800 kHz and 1.6 MHz bandwidth, which are permitted by the FCC in 15.247. As far as I know there's not actually anything particular to 2.4 GHz allowing higher throughput for LoRa than that the corresponding Semtech chip happens to support wider bandwidths. (I.e. no legal barrier.) The tradeoff is less range due to lower…
What issues does it create for others to use too narrow of a bandwidth? Why “should” the FCC care if someone is only using a small portion of the spectrum that would otherwise be fine fr them to use? Thanks for educating us!
It's a mechanism to try to make the 900Mhz band more useful to uncoordinated users.
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It doesn't surprise me. This is a deep networking problem and very few CS people know anything about networking or how to design clean, fast, low-overhead network protocols and systems. If IP were designed today the packets would have 500+ bytes of plain text JSON as headers and the spec would support hundreds of extensions.
Have you seen that IPvwhatever proposal from a handful of weeks back that has OAuth/OIDC in packet spec
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LoRa would go much farther than Wifi on 2.4ghz. Lora uses Chirp Spread Spectrum (CSS) modulation while wifi uses OFDM (Orthogonal Frequency Division Multiplexing). The first being designed for extreme range while the latter for bandwidth. At 2.4ghz you could probably get LoRa connections up to 6 miles with the right antenna height.
6 miles seems a very optimistic estimation: 2.4Ghz propagation is very reduced by obstacles like buildings or trees and at that frequency the atmospheric water (fog, rain, humidity) have a big impact on propagation. And you need also to consider that 2.4Ghz is a very polluted band, then the noise floor is significatevly higher than in the 865/915 Mhz. Moreover at 2.4Ghz the Fresnel window is smaller and the risk of m…
WiFi sensitivity is about -90dB, while LoRa sensitivity is around-150dB…. So that’s about a million times more sensitive. So you need about a million times more signal strength to use low bandwidth WiFi (still impossibly fast by LoRa standards) than to use low bandwidth LoRa.
Those are radio specifications. Real links require about 10db more to get any kind of reliability, but the comparison stands.
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We may see a day when the internet is not available, or when interacting with it represents an unacceptable risk. It's a good idea to know how to set up your own.
In that day whatever is jamming starlink will just jam mesh radio too. It'll likely be even easier.
The mesh networks are dealing with, by definition, a sparse and widely distributed set of devices which are independently configured and controlled, and in their current widely available form are only dealing with terrestrial communication. Without that point of centralisation you would need to focus on targetted regional jamming, as from a practical standpoint you cannot perform wideband RF jamming over an entire country - signal jammers don't scale that well, and geographic features come into play. As an example you might effectively block mesh networks from operating reliably in a given city, but if people were to move outside of that area then the mesh would operate again. Geography is both a strength and a weakness here: a mountain range will impede direct communication with someone on the other side, but it will also have the same effect on jammers which will vastly increase the cost to deploy them in a ubiquitous fashion.
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In that day whatever is jamming starlink will just jam mesh radio too. It'll likely be even easier.
That’s really the killer for survivalist mesh ideas. It’s trivially easy to jam, and if it’s open it’s also easy to DDOS. Jamming is done in military scenarios too, but in that case it’s limited by the fact that a jammer is a big transmitter painting itself with a big sign that says “fire missile here.” Civilian mesh doesn’t have that fallback.
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In that day whatever is jamming starlink will just jam mesh radio too. It'll likely be even easier.
That’s really the killer for survivalist mesh ideas. It’s trivially easy to jam, and if it’s open it’s also easy to DDOS. Jamming is done in military scenarios too, but in that case it’s limited by the fact that a jammer is a big transmitter painting itself with a big sign that says “fire missile here.” Civilian mesh doesn’t have that fallback.
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It sucks how everything feels like a toy. I think meshtastic is the closest thing to a “product”. They made a bunch of bad architectural decisions that are haunting them now like how nodes broadcast its info.
Because they are toys. For real work it makes so much more sense to use the internet. With the new satellite tech you can reach the internet everywhere. Mesh radio is a fun way to chat with radio nerds in your area. Not a serious infrastructure.
Meshtastic should be the obvious answer for this but in my limited experience the app(s) and code are buggy on even the most typical hardware. Wish it wasn’t the case but it is.