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Long-Range Networking
ink and several others sent in the latest Cringely column where he discusses creating a long-range 802.11b network using high-tech tools like a telescope and bribery. Sean Clifford sent in guide to creating your own long-range antenna: "Have some old PrimeStar hardware laying around? Do something useful with it by turning it into an IEEE 802.11 wireless networking antenna. This electrical engineering professor uses an Airport, but any access point should work fine." If you're at all interested in this sort of stuff, get involved with one of the community wireless networks springing up.
There's a few wireless ISPs that have been using 802.11 for long distance shots for quite a long time..
Longest one I ever did was 13 miles with no amplification, using standard 24 dBi antennas. That was over 2 years ago (yes I know it wasn't 802.11 back then, but basically the same 2.4gHz wireless networking gear.)
While it may be "l33t" to hack old primestar gear to make a shot, you're not coming up with anything new.. for a couple hundred bucks you could buy two 24 dBi antennas and easily make line of sight shots over 10 miles with no amplification.
At close distances, it'll punch through quite a bit. I run an Airport card in a G4 as my "base", and a stock Wavelan Gold card in my laptop as the remote system. Both run Slackware, and are configured in the "old ad-hoc mode" which lets you just ifconfig the interfaces with reasonable numbers and it just works.
As for distance, I can go about 150 feet in most directions, including getting out of my house, crossing the yard, and getting through the walls into another house. It starts getting touchy inside the next building, but that's life. The point was to have total coverage inside my place and the yard immediately surrounding it, and I have succeeded.
The next step is to get some antenna action happening so I can light up even more space with the signal. Right now, everything is stock and it's still amazing just how well it works.
Even if the airport is just a lucent card in disguise. The antenna and base have not been certified together. A no no.
Not true. the law is a bit complex, but it isn't definatly illegal to work to modified one off equipment. It is illegal to sell such equipment, but the requirement is that modified equipment be professionally installed. If your not breaking any noise or power requlations and your installation looks nice, then you have a reasonably arguement that your setup was professionally installed by you.
If that will hold up in court depends on the judge and jury, but generally it won't go that far because the FCC has better things to do then worry about someone on a license free band who isn't breaking power limits.
You said:
Also is it legal? I could just see the FCC knocking on someone's door for this.
Also what about diameter, do you have to be in direct sight of it, or will it work though walls and if you are off to the left 50 feet?
The article goes into both of these:
1) the fcc only cares about signels over a certain strength. This lives comfortably below that threshold.
2) Yes, this must be line of site. Cringely went looking through three different telescopes to find someone to work with.
Zapman
Why would you think there's any HTML in my post? Does it show up that way in your browser or something?
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Could you name the community where this happened? Or better yet provide a link to a news story about it? I'd like to know more, if only to avoid ever passing through there.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
If you really were the time would be 25 or 6 to 4.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Isn't line of sight basically a 2 node network? Does it really make sense to use a protocol that worries about polling and collision detection when RTR and RTS should handle it just fine?
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Cringely's satellite setup had a crap uplink which I assume was dialup. Assuming the satellite downlink is 2 Mbps, and the modem 33.6 Kbps on the uplink, the ratio between downlink and uplink is about 60.
On a big download, he would receive Ethernet style 1500 byte packets on the downlink, and send 40 byte TCP ACKs on the uplink. Unfortunately 1500 / 40 is 37.5 - he would need to send 2,000,000 / 37.5 = 53 Kbps of ACK packets over his 33.6 modem, so his downlink is reduced to about 1.3 Mbps when he's using TCP.
This is a bit of an artificial example but it does illustrate why extreme asymmetry is a bad idea with TCP, and of course any other traffic on the uplink would slow things even more. There is some work on optimising TCP to solve this, e.g. ACK filtering and ACK reconstruction.
BTW, high latency still sucks because TCP's ability to ramp up its congestion window after some packet losses is controlled by the round trip timer - high latency means a slow ramp up after every significant loss, which is particularly bad if you go into slow start and have to start from one packet again.
In this case it was probably more latency than asymmetry because his link was unlikely to be 2 Mbps.
I've set up similar networks. However, I managed without the dish, and instead of coax I used string.
Strangely, it was much easier to use it for VoIP than Email, Web, or Quake.
Know what I like about atheists? I've yet to meet one that believes God is on their side.
The power limits are further constrained by the requirement to use the minimum power necessary to achieve communications, and the need to control uwave RF exposure to people near the antenna.
Plus generating that much power at 2.4 GHz is EXPENSIVE as well as unecessary.
True, but the FCC regulations for the Amateur Service place limitations on the content you can send, use of encryption, and other restrictions that may make "souping up" an 802.11b system more useful.
What kind of losses do I get firing through trees?
as many cant put up 100 foot towers to get over the trees here in suburbia If my target is less than 5280 feet away will 22DBi gain burn through the trees inbetween?
(I'd calculate it but I cant find my ARRL antenna handbook.)
Do not look at laser with remaining good eye.
Agreed. In support of this, we provide a free courtesy LANRoamer account to anyone who runs an open access point that meets the other LANRoamer criteria (up most of the time, in our coverage maps, technical contact info provided, etc.).
I don't think this policy is on our web page yet, but it will be soon and we publicly stated it in our presentation at the last sbay.org meeting, and possibly in our presentation at the last Bay Area Wireless User Group meeting.
Goofy. Aside from a bad antennae connection, perhaps you should try replacing one/both units?
;). Maybe a neighbor has his experimental microwave weapon pointed at you.
It only takes a small nick in the antennae connection to screw things up horribly, though... 2.4ghz is quite sensitive to that.
Time to get out your Rhode & Schwartz spectrum analyzer and check out what's goin down in your airspace
External 'diversity' antennas? Is that when there are two omni's, one on either side of the unit? Gah.
Cool.
Good luck with the yagi. I know we've used them lots and they make a huge difference.
ANy place you can borrow a spectrum analyzer? One of the local hammies or a cellular tech will have one in his truck.... maybe for a case of beer a cellular guy will come over and sweep the place?
If you are in some country with a monopolistic government, some small carribean island, then I might believe this.
As for the US, I doubt it.. I don't believe there are civic laws regarding providing telcommunications.
You have an RF problem somwhere.A 20 foot unblocked airspace should provide no discernable difference, at least, not on the software meter they show.
Linksys tends to be reliable.
Do they have internal or external antennae? Do you have any other 2.4Ghz products? Cordless phone? Video transmitter?
Does your microwave leak?
Also, what exact model of card are you using? What's it's output power (not that it'll be the problem)
Also, what's the wall made of? 2.4Ghz doesn't like going through concrete either. It doesn't like going through much of anything, actually. Thin wooden walls in the house will be okay, thin partitions in offices are okay.... thick wooden walls present a large barrier.
- 802.11 has specifications for doing exactly this kind of link
- Yes, a customized protocol tuned for exactly the distance you are going would be more efficient, but you'd have to write it, and you wouldn't get that much of an improvement.
- 802.11b does not do collision detection, it does collision avoidance (has to do with timers). You cannot detect a collision reliably in RF, especially at these distances.
- The lack of collision detection is one reason why you need rts/cts and other types of handshaking. The other is radio noise.
- 802.11b doesn't poll (I don't think.)
- Adjustments to the inter-frame gap in 802.11b (if memory serves) to account for increased distance can cut down largely on the # of collisions, but decreases the available slot time, so a transmitter may have to wait longer to transmit, but will transmit faster once it goes.
- This can be extended into 3 node, or other configurations where not all stations can see each other; 802.11b can deal with this as well.
If he is right about the antenna being 21dB then it is most likely to be illegal.
Most 802.11b cards put out about +12 to +15dBm, some more than that. +12 + 21 = an effective radiated power of +33dBm. The FCC limits for the 2.4GHz band where 802.11b lives is 1W maximum, i.e. +30dBm.
His set-up is most certainly illegal. The FCC cares about the effective power, not the power fed to the antenna.
Also, if you are using a +21dB antenna and you are 50ft off, it is probably not going work. A +21dB antenna is going to have a _very_ narrow beamwidth.
Absolute statements are never true
So at some point it makes no sense in making more directional antennas, as you have to decrease the power level accordingly.
See this link for more information.
When I first read this article.. I was chuckling at his ingenuity..and determination...sweet... Then I thought..To help subsizde his monthly cost and his inital outlay..talk to his neighbors.. I'm sure the signal isn;t so omnidirectional that the radio signal goes straight to his house without any spill over.. He can set his neighbors up on 802.11b as well,, charge them a modest fee and he can be come is own neighborhood ISP..
I'll be damned, I've never heard of that. That's insanely cool!
Dahlmann tightly grips the knife, which he may have no idea how to use, and steps out into the plain.
True, but I can't believe they even let you try, without at least a ham license. Very un-governmental of them. :)
Dahlmann tightly grips the knife, which he may have no idea how to use, and steps out into the plain.
This is all covered under the Part 15 section for homemade electronic devices.
I've never heard of that. What subpart is it under? That's cool, if true.
Dahlmann tightly grips the knife, which he may have no idea how to use, and steps out into the plain.
I assume he didn't spend $2K just to play Doom.
Oh, I don't know. I spent way more than that building this just to play Quake...
Dahlmann tightly grips the knife, which he may have no idea how to use, and steps out into the plain.
-- ;-)
Kuro5hin.org: where the good times never end.
I would say no. There's only a couple places that power can go:
Point to point microwave links for such things are available, although they're not common consumer items.
Incidentally, links like this need some extra gain margin if you want them to keep working during heavy rain. Rain passes gigahertz frequencies about as well as it passes light.
...making your private network availible to even more people.
First lets work out the security holes (of wireless networks) and make sure the admins can properly configure them before proclaiming wireless networks "the coolest thing since sliced bread".
There are way too many companies out there who have just lept into the wireless market with both feet and later found out that any Tom, Dick and Harry had access to their network (example: *cough* Sun *cough*)
- Can someone help me off of my soapbox?
"A plan fiendishly clever in its intricacies"- Homer Simpson
What is the distance on these things (prime star hack)?
Also is it legal? I could just see the FCC knocking on someone's door for this.
Also what about diameter, do you have to be in direct sight of it, or will it work though walls and if you are off to the left 50 feet?
"`Ford, you're turning into a penguin. Stop it.'" -THHGTTG
Section 15.23. "Equipment authorization is not required for devices that are not marketed, are not constructed from a kit, and are built in quantities of five or less for personal use."
ok then your [sic] infringing on my copyright! Could you as [sic] me next time before STEALING my comments for your own?
A complete list of free wireless projects at PersonalTelco.
And will someone explain to me why latency is important? I assume he didn't spend $2K just to play Doom. For a server? If I ever spring for a dedicated server, it will live in a web farm, not behind an unrealiable 1 megabit DSL link.
__
Oh, and don't you think you should just buy banner space on Slashdot instead? It's probably a lot more effective.
--
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( \
X
Friends don't let friends use multiple inheritance.
If you'd like to see just how much an ISP cares about policing its network, go to grc.com and read his account of tracking down Denial of Service attacks on his system. He had clear evidence of hacked machines running as zombies, hijacked dial-in accounts, etc. and got exactly zero interest from the ISPs on whose customers were being exploited. The entire story is a fascinating read on how he tracked down the perpetrators of these sort of attacks and got it stopped (no thanks to the ISPs or law enforecment).
I checked a recent link about designing Airport nets and some other Airport sites. They don't reveal any clues about this being possible.
I checked the Cisco/Aironet site. For the 340 Series WLAN gear they have a product called an Ethernet Bridge which is what you would use to do what Cringely said he did. This is different from their Access Points and Base stations . A Cisco base station looks to be equivalent to an Airport.
Does anyone have any references on how to do this with an Airport? I'm finding Cringely's story a little hard to believe.
Kevin
"They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety"-B.Franklin
Why not use a standard LNB module instead of a juice can? Is it not possible to transmit with one of those? How about one from those 2-way dishes (is there even any difference)?
Microshaft still OWNZ JOO!
SIG: HUP
If the guy gets a 20db gain from his setup, then who cares? He got it to work, he's not selling the equipment to you, if you try it YMMV, etc, etc.
So, either you say "this guy isn't getting a 20db gain" and prove it, or drop the whole impromptu /. EE course and admit it just plain works! Obviously, he's not too far off the calculations (too far being defined as not getting his needed 20db gain from the setup) or he's lying about the gain. Which is it?
When done correctly, you can get a 20 mile + link setup. The operative word being CORRECTLY!!!
The tin can antennas are not correct, nor is altering a wLAN card to do something it isn't ment to do. Use a Cisco AIR-PCI352 or AIR-LMC352 100mw card for your long range wireless links, and the correct antenna + cable.
We do this legally and professionally; we have many antennas, cables, amps, and other accessories. We also have complete long-range pre-built systems
Donald Beckman
Techsplanet.com
Wireless sales @ www.techsplanet.com/wlan
I still think RFC1149 is a better, and cheaper alternative! ;-)
I'm only trying to go 200 yards line of sight, so I just want a very simple/cheap antenna - I figure if even the simpler 802.11 designs are made to go 1Km or more, then I can afford to botch it a little.
Also I was wondering - is it a good idea to intentionally "de-tune" an antenna, to reduce it's output to just what you need (as opposed to using an attenuator). I don't want the FCC knocking on my door because I'm interfering with all the cordless phones in my neighborhood.
Here's a link to some 2.4GHz antennas. Has anybody here experimented with these designs?
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It is illegal to *run* a setup using an antenna (omnidirectional, yagi, dish, parabolic mesh), cable (you soldered it up), OR amp, if any part of the setup is something you slapped together.
The setup you purchase, from the card to the cable (to the amp) to the antenna must be certified altogether. iow, it must be sold specificly and unmodified, or must have been certified for installation by an FCC licensed installer.
If you have a WaveLAN/Orinoco card, you have to buy Lucent's antennas or antennas approved to work with Lucent's card. If you construct your own antenna, you can use it on your card as long as it's been approved.
You see a lot of sites about soldering some coax cable, constructing antennas out of wire clothes hangers, or using adapters to fit the external antenna plugs on some of these 802.11b cards...they are all nifty, cool, etc., but if they run their setup and did not get it checked by an FCC licensed/approved installer, it's an illegal setup.
I'm not saying that it won't be within regs. I'm not saying these setups are bad and evil. I'm saying that, if someone finds out, whether by social interaction (you talk) or stray emissions (neighbor doesn't like your ugly dish), and the FCC comes knocking, you can be fined up to $150,000. Not cool.
When people hear this, they get all huffy and puffy about "how their installation" works and isn't harming anyone, or how they won't get caught. Blah blah. I'm not commenting on whether it works or not. Don't flame the messenger--that's what the regs state.
btw, this issue has been brought up by others in other /. posts after stories involving 802.11b setups, esp. the earlier ones. Look for some of the +5 posts.
this reminds me of those folk who THINK that putting a bunch of aluminum around the ends of their (old) TV antenna's actually make the thing work better.
Hell, if it works, fuck the math and milling out expensive blocks of aluminum! I used to strategicaly put an empty soda can next to my wireless card when too many cars were parked between my house and my neighbor down the street. When it started to rain, we had to break out the aluminum foil.
Technically, there are no power limits for certain amateur radio license holders in the 2.4GHz range other than those that address interference to the primary allocation holder (amateur radio is secondary in the 2.4GHz range). Plus, amateurs are permitted under FCC regulation to modify their equipment (including commmercial equipment) as long as the mods do not generate interference above certain limits.
This is quite interesting...
SWR - who needs to be concerned with that...
Wavelength of the feedhorn - who needs to be concerned with that...
There is a reason that standard feedhorns are patterned out of machined steel/aluminum - dimensional control. The size AND shape of the feedhorn is critical for proper (and efficient) transfer of energy from the wire to the waveguide/air. Even the shape of the exciter element (the 1.15" wire soldered to the end of the RF connector) is quite important.
Then again, this reminds me of those folk who THINK that putting a bunch of aluminum around the ends of their (old) TV antenna's actually make the thing work better. It works for one articulate idiot so the rest of the world jumps right in. Can anyone say "Lemmings"?
Ron Gage - Westland, MI
Apropos to community networks, I'd like to make a shameless plug for a GPL-compatible open source gateway and settlement system, downloadable from ftp://ftp.lanroamer.net/pub/lanroamer. The backend software will also be released under GPL later this weekend. There is obviously a business behind it, but the software and the ideas are relevant to this article in their own right. The basic idea is that whoever puts up an access point gets free use of the everyone else's access points and a significant share of share of the revenues from paying customers (expected cost to paying customers: $20-$25/month). We are in the process of setting up a sourceforge area for the software as well. Finally, if you're curious about future development direction, you might want to check out the current wish list, although completely different additions to this list and, better yet, contributed code are welcome.
At first when I read the summary of the article, I was thinking that he was going to somehow use those telescopes to actually DO the networking instead of just using them to find a house.
:)
In fact, I kept thinking this beyond the point where he was talking about street lights and stop lights.
I wonder, how feasible could such a system be? If I had a high powered light bulb (or some other convienent light source) that could switch on and off very rapidly, then at the other end of the "network" have a telescope with a CCD camera watching the light, as long as the telescope never moved, data could be sent at a rate equal to the speed at which the light could be toggled.
I can see a great number of potential obstacles to this which would make it difficult to use in a production environment. But it would be a cool hack nevertheless.
-Restil
Play with my webcams and lights here
Here is a Low Cost Wireless Network How-To.
It covers the technical details that the other wireless networking sites miss. It has amplifier ideas and schematics and external antenna mods using old MMDS dishes. It even has CGIs for preforming wireless link analysis.
Airport is ideal for this sort of project - the base stations are relatively inexpensive, and they can be easily configured without a Mac - one fellow wrote a Java-based configurator app. They also work with pretty much any wireless card out there, AFAIK. I also use a Linksys with mine for one of my Wintel boxes.
I took my Airport and added the Lucent range extender antenna (about $60), and simply dremeled my base station to accept the antenna mount. I've been using it for about a year and a half now, and it gives me an effective range of about a quarter mile (it helps that I mounted the whole rig on an outer wall upstairs in my house) when used with my iBook.
To go much farther you either need more power (which may tick off our friends at the FCC) or directional antennas, like Cringely used, with clear line-of-sight. You're subject to all limitations of the 2.4 GHz band, though, and a lot of current cordless phones run in that range - it can mess up 802.11 signals somewhat.
I stick to 900 MHz digital phones partly for that reason.
- -Josh Turiel
-- Josh Turiel
"2. Do not eat iPod Shuffle."
Tim Pozar's page The FCC's Part15 Rules and Regulation and 802.11b emissions in the ISM 2.4GHz Band discusses this and has links to the regulations and other useful references. Look for the section titled "Fixed, point-to-point paths and get even more power."