Making 802.11 Take The Longshot

Simone from O'Reilly pointed out the continuing developments with Rob Flickenger & Co's efforts with 802.11. This time around they're trying to make a five mile to homes, via a 20.9 mile boost antennae. Fun for the whole wireless family.

Comments

Re:FCC rules for 802.11 and fines up to $250,000

[bluGill]

Accually you don't need a $200 installation geek. Your equipment must be either professionally installed, or certified. However the definition of a professional is pretty meaningless. If you are paid to do something you are a professional, which says nothing about your ability to do it right.

Note that you still need to meet regulations. So if you put a 500 watt amp on your signal they will get you, no matter how professional your system is put up. (.5 watts is the biggest amplifer you can buy, and even then the manufactures make a big deal that you cannot run the better antennas with it)

Re:Legality?

[mikeb]

I think the regulation in the US isn't that much different from in the UK (from where I speak). The limit here is based on ERP, effective radiated power.

The low-power cards pump out around a couple of hundred milliwatts. You can plug them into hi-gain antennae, in which case the ERP in the direction of the beam is increased. Increase that above a certain limit (depends on your Government's regulations) and you go outside the permitted level. Alternatively you can use an amplifier and a lower-gain antenna. Whether you get X decibels of gain from the antenna or the amplifier really doesn't matter, it's the peak energy density coming out that counts.

If you can't remember the math, it may help to know that decibels add: 10dB from the antenna plus 10dB from the amp = 20dB of gain. Decibels are based on logarithms base 10. 3dB = factor of 2 gain, 10dB = factor of 10, 20dB = factor of 100, 30dB = factor of 1000. 200mW into a 20dB antenna is theoretically equivalent to 20W into an omnidirectional atenna (but we call 'em aerials over here, at least if you are as old as I am).

In reality, you would never get the theoretical power, because feeder and mismatch losses in the connectors can easily lose you several dB, much more if you are careless. 10dB loss in connector and feeder would be no surprise. 2.4GHz is where you start to need plumbing and wires get more and more tricky to work with.

More to security than just your mail

[rakjr]

You are right that it usually does not matter who reads your e-mail. But it does matter when it comes to who is using the paid for resource. As more things go wireless, unless there is some kind of major security improvement, we are going to see a monster of a problem. Just like it used to be ok to leave your house unlocked. The emphasis being on "used to be."To be honest, I am surprised that people have not started stealing power via a fuel cell system from live outlets on the outsides of homes.

Legality?

[mindstrm]

I wish I could quote the math, but I just don't know it that well. What I do know, from working quite a bit with basically this same thing, is this.

It's not accurate to say 'you can't use an amplifier' nor 'if you don't use an amplifier, whatever you do is legal.'. Both can keep you with the bounds of the ISM rules, or take you outside of it, depending on what you do.

The point is, the right high-gain directional antennae alone can take you outside the technically legal limits of 2.4Ghz ISM. And other situations, you can amplify the signal as long as you stay within the specified limits.

Anyone with some real knowledge of the math involved want to explain this better? (Or correct me?)

Re:Legality?

[flatulus]

Thank you for raising the question. This *IS* a legitimate concern!

In the U.S., the FCC has established EIRP limits on Part 15 spread spectrum applications (which includes 802.11 in all its forms). Other countries have their own limits - generally more strict than the U.S., IIRC

The Part 15 limits on EIRP go something like this:

a) You are allowed up to 1 watt (+30dBm) output from your transmitter.

b) You are allowed up to +6dB antenna gain (over isotropic) with a 1 watt transmitter.

c) For every dB reduction in transmitter output, you are allowed a corresponding dB in antenna gain.

In essence, this means that you are limited to +36dBm EIRP (effective isotropic radiated power). I do not know whether you can subtract transmission line/connector losses from this.

Most 802.11b transmitters are at about 30 mW, or -15 dBm. In other words, you are 15 dB below the maximum allowed transmitter power. So your antenna gain must not exceed 15 + 6 or 21 dB. Judging from the pictures in the article, it looks like they are using dish antennae with probably 23 dB of gain.

Also: The 30 mW transmit power output is an assumption -- Some radios can output 100 mW. This would reduce the legal antenna gain from 21 dB to 16 dB, which would almost certainly push them past the legal limit.

Not that I expect the FBI SWAT team to knock down your door :), but just thought I would point out that the amount of antenna gain you can utilize - and stay legal - is finite.

This topic concerns me because the more that is said in a public forum (such as this story), the more likely the FCC will be to tighten up on 802.11b uses. I have already heard that the FCC is considering making it illegal to manufacture a Part 15 transmitter (which all U.S. 802.11b products are) with an external antenna, for this very reason. I hope that does not come to pass...

Trying..

[mindstrm]

But they haven't done it yet, though it's quite likely.

I've seen approximately 20 km links using 2.4Ghz ISM band, staying within the limits of the ISM band.

5 miles is no biggie; we were doing that 3 years ago or so with Proxim RangeLAN cards & some good antennae.

READ -- interesting.

[mindstrm]

There is an added benefit you didn't mention for the US.
For each dB of cable loss or dB of reduced output power, you can add 3dBi of antennae gain, PROVIDED the connection you are making is point to point, and fixed (not mobile). This allows for much longer ptp links than are possible in Canada, for instance, where the rules are simpler (EIRP of 36dBm, period).
So a 20 mile link is probaby quite easily done, provided the connectors and antenna work is top noch (2.4Ghz is sensitive to small errors in cabling, etc).

ALso, and I can't confirm this absolutely, but I know when you get things approved for ISM band in the US, you have to specify the cable length/type and antennae type, and you have to use non-standard antennae connectors (if they aren't fixed or internal). This is because they are techniaclly not supposed to be modified, as if you change any component, you are creating an unapproved transmitter.

Hemos is new to the English language

[novarese]

This time around they're trying to make a five mile to homes, via a 20.9 mile boost antennae.

For those of you in the audience who just said to your self "what the fuck is he talking about?", a quick translation/clarification from the actual story:

This series of articles tracks our progress in trying to use the 802.11b protocol to create a link from Sebastopol to a hilltop tower 20.9 miles north, and from there on to some homes 5 miles across a valley.

Not that I blame Hemos, I know how hard it must be to "edit" these submissions.

Re:Discovering America?

[Keeper ofthe Keys]

The limits here in the US is 1 watt ERP. With the antenna they are showing in the articule, (I use the same one) and using the Orinoco Silver card, (I use the Gold card) they are illegal with that set up.

Actually, for point to point links, the maximum EIRP is 48dbm (total system power), but you must reduce output power by 3db for each 6db added with antenna.

For normal point to multipoint, the EIRP is 36dbm (4W total system power) but the power output of the radio/amplifier cannot exceed 1W (30db).

Re:brokent link? n/t

[marienf]

just an unbalanced quote in the href.
remove the last quote from the URL and you'll be fine.

Shouldn't be too hard...

[electricmonk]

...but what's the point? There's already some pretty inexpensive equipment that'll do long range point-to-point connections

Also, with the questionable security of 802.11, even with WEP enabled, would it really be that good of an idea to have that large of a coverage radius? With technology like this, people wouldn't even have to drive up to the parking lot to gain access to the network, they could do it from their home or someplace far away from their actual target.

It's a security breach waiting to happen.

Re:Shouldn't be too hard...

[electricmonk]

When I used the term "questionable security," I was including the fact that it would be trivial to gain access to the network and compromise the servers there.

Re:Shouldn't be too hard...

[boaworm]

Well, even if its a security problem with it, it can sure be useful. I mean.. is every data in need of being secure ?

Say you live far out from the city, and you can pick between a lowspeed modem or a lot faster radio lan. What would you pick ?

With some encryption, say encrypted webproxy at the ISP, encrypted mail etc, i'd definitly go for it if the alternative was modems. And many things you do online doesnt even require security... i dont really care if someone eavesdrops my slashdot browsing :)

Re:Shouldn't be too hard...

[ConsumedByTV]

I live near this area.

I want to say that Orielly gives back to the community.

What few people might try and break this would be out numbered by the number of people that would pay for this sort of thing.
The number of people that would be beniftied by this would be great. Schools would have highspeed access, kids who wouldnt have access otherwise.
And yes it is possible to do long range point to point, but then you have to hook it up to each computer.There inlies your real cost, your real reason for having a DMZ on an 802.11 network.

This is a great idea and I forone am going to go out there with my laptop as soon as I get my new lucent 802.11 card.



Are you on the Sfglj (SF-Goth EMail Junkies List) ?

Low power cards are NOT couple hundred mw!

[Totally_Lost]

Nearly all 802.11b cards come in two flavors roughly 30mw and 100mw due to the power amplifier design of the three most common radio chipsets. Aironet 4800 series and other PRISIM I designs are mostly 100mw, nearly all Lucent, PRISM II and II.5 are 30mw with the exception of the Cisco 350 series which is also 100mw.

There were a few early 802.11 Prism I cards that were 250mw and 500mw produced by minor players in the market. And I believe the same is true of 802.11 FHSS vendors - mostly 100mw.

It's pretty hard to connect a 30mw radio to a 23dBi dish without any cable and connectors losses. Especially given that it generally takes an RG316 jumper to get from the PCMCIA card to some more managable connector for the antenna. Typically lose 1-3 dBi between the radio power amp and the antenna feed element even with short cables and best connectors.

Most people mistake that dBi and dBm are the same, converting 24dBi to dBm we get 24-2.1=21.9dBm EIRP is predicted then to be roughly 13 + 20.8 - 2 = 32.9 dBm for most 30mw radios connected to a Conifer 24dBi dish typical. These leaves a safety margin of 3.1 dBm for radio power, cable and antenna variances, and still remain inside the FCC 36dBm EIRP budget.

Most standard RF cables and connectors do not work well with 802.11b at 2.4GHz. But Times Microwave cable and connectors are excellent - most people use LMR-400 and LMR-600 with TM gold pin connectors for minimum losses. The times cable has the best propagation velocity factor in the industry, which greatly minimizes wave front compression and associated phase distortion in the encoded digital signal.

100' of TMR-600 costs about $165 plus two TM "N" connectors that are $23/ea - for about $220 assembled. The cable and connector loss is about 4.1 to 4.5 dBm. 100' of TMR-400 with connectors is about $130 and 9-10 dBm of loss. Beldon 9813 "LOOKS" almost identical to LMR-400, but has a much slower propagation velocity factor, and often will not work at 11mbps in cable lengths over 25', even though the two have nearly the same RF attenuation at 2.4GHz. A lot of older vendor cables from 1-2mbps 802.11 days are Beldon ... beware tring to make them work at 11mbps.

ALso beware of center pins plated with other than gold - since the RF at these frequencies will accelerate oxidation which will rapidly change the connector impedance and the cable will "ring" with standing waves if anywhere near a wavelength multiple. Symptoms are good signal strength reported by radios in both directions, but very high retry rates caused by either garbling of the encoded signal and/or the ringing not settling down fast enough to recieve the 802.11 ACK packet.

Similar symptoms are also had when a "passive re-radiator" element is near the beam path at either end - a section of metal near a multiple of the wave length which rings during transmit, and the ringing doesn't die down fast enough to recieve the ACK packet.

Re:boosting airport?

[Totally_Lost]

Oh ... and I forgot the $150,000 fine for personal violations, and $250,000 fine for commercial violations, could make it the most expensive "boosting" around :(

FCC rules for 802.11 and fines up to $250,000

[Totally_Lost]

Everyone should consider that it is illegal to mix and match arbitrary 2.4Gz gear, unless you employ the services of what the O'Reilly guys call "an FCC-approved installation geek at $200 per visit" who are required to make sure the installation is legal as required by Part 15 Regs.

While it is pretty easy to buy off the self antennas for 2.4GHz on Ebay or mail-order, there are very few vendors who sell certified configurations approved by the FCC for use with specific 802.11 vendors gear. Companies like Winncom and Hyperlink have done the required FCC certifications (which typically cost $15-30K) and can sell kitted systems - radio, cable, antennas to allow self installation of an FCC legal configuration. Otherwise, attempting to save a few hundred bucks is likely to net $250,000 in fines per installation as soon as a competitor (either in the wireless business or your trade) attempts to level the playing field with a complaint to the FCC.

When I was at Networld/Interop last year several of the wireless vendors were quick to note FCC raids in the south brought on by ISP's home brewing illegal configurations that violated the specs.

We have been doing what the O'Reilly boys are trying for several years now, and have a strict policy in our customer base to purchase approved kits from Winncom AND to use professional installation to make sure our network remains legal.

Multipoint links out to 25 miles are not that difficult - but it's also not a piece of cake using commercial hill top radio sites - especially when microwave links, AM/FM/TV broadcast stations, Cell Operators, Paging Operator, 400/800MHz moble repeaters, and other high power transmitters are on or near the tower. These transmitters all product Broad Band Noise (white noise) in their power amplifiers which greatly increase the noise into the 802.11 radio's reciever - often making the receiver deaf to your signals at distances further than a few miles - no amount of filtering will solve this problem, only careful trial and error placement of your antenna will minimize, but not remove the problem. Secondary to this, is the fact that snow, fog, rain, hail at the site will cause reflection/defraction of the broadband noise back into your antenna making the reciever deaf under cetain weather conditions that would not otherwise impair the link.

Also there is a problem with the transmit energy from co-located gear at the site mixing in your amplifier and radio front end, producing harmonic products of your radio's IF frequencies, which go right thru the filters and deafen your radio for as long as the RF carriers are present. We run with 110dB of band pass filter between a 7dBi omni and amplifier/radio to suppress this "Intermod". Reciently one of the PCS cell carriers doubled the number of channels at two sites we share, and seriously disrupted our repeaters for 30-90 minutes at a time - until we identified the source of the problem and added an additional 40dBi of band pass filter. We still see several second hits off the 3rd and 5th harmonics of 400/800Mhz pagers/mobile communications due to the extremely high EIRP they transmit at (several hundred watts). Even though their out of band energy is legal (50-70dB down from their primary carrier) it deafen's our recievers for brief periods due to near-far problems (IE our incoming signal is down around -80dBm - their harmonics are -40 to -10 dBm at the repeaters antenna.

It has taken us 6 weeks of trial and error placement and equipment/cable tuning to make some hill top repeater sites usable. This is not a binary problem where it just plugs and plays after hooking up some wires.

So in short, Metropolitan Area Networks built from off the shelf 802.11 wireless lan gear using repeaters over commercial radio hill tops sites isn't always easy to make links more than 2-3 miles work reliably. Even using this this gear shorter distances across roof tops is often difficult due to diffraction losses caused by the buildings and trees, and other Fresnel zone violations resulting in multipath interference that varies with temperature and weather. On some of our longer (IE weaker) links we have even seen Solar radition interference patterns on radios with west facing dishes as the sun sets at times. And other links installed in the winter, where a tree 90' away, and 40' to the side of the beam, leafed out and disrupted the link. And where standing waves from metal building 400' away at 10 O'clock to the beam, nulled out the beam at certain times of the day probably due to the metal siding warping in the heat and changing the pattern reflected back at the side of the dish antenna.

So do your homework before tring to save a few bucks buy 3rd party 802.11 gear from vendors that have not done the required certification with each radio you have. The several million in fines if you get caught is not a savings. You probably want to get a spectrum analyzer for the 2.4GHz band before you start that has a calibrated dBm vertical scale - like the HP8559s and later series of SA's. You will also need a display which offers "Max Hold", with an 8559A this means an 853A digial display, not a 180 series display. Trying to debug metropolitan area wireless lan's without being able to see the spectrum is nearly impossible - and horribly frustrating.

For more information of microwave path issues, check out:
http://www.tapr.org/tapr/html/ve3jf.dcc97/ve3jf.dc c97.html

For FCC regs see:
http://www.fcc.gov/oet/info/rules/
Also checkout the fines section elsewhere on the site.
Extracted from current FCC Regs, Part 15

PART 15 - RADIO FREQUENCY DEVICES
Subpart C - Intentional Radiators Section
Section 15.203 Antenna requirement.
An intentional radiator shall be designed to ensure that no antenna other than that furnished by the responsible party shall be used with the device. The use of a permanently attached antenna or of an antenna that uses a unique coupling to the intentional radiator shall be considered sufficient to comply with the provisions of this Section. The manufacturer may design the unit so that a broken antenna can be replaced by the user, but the use of a standard antenna jack or electrical connector is prohibited. [...] Further, this requirement does not apply to intentional radiators that must be professionally installed, such as perimeter protection systems and some field disturbance sensors, or to other intentional radiators which, in accordance with Section 15.31(d), must be measured at the installation site. However, the installer shall be responsible for ensuring that the proper antenna is employed so that the limits in this Part are not exceeded.

Section 15.204 External radio frequency power amplifiers and antenna modifications.
(c) Only the antenna with which an intentional radiator is authorized may be used with the intentional radiator.