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Inspiring Adventures in SF Wireless Networking 154

Posted by chrisd from the and-you-too-can-be-wirelessly-groovy dept.
JimDog writes "Here's a description I wrote of how I set up a point-to-point 802.11b link over 3.5 miles for Internet access at my house. The link runs at 3.5 Mbps, which I barely make a dent in, and I'd like to offer the rest of the bandwidth to anyone who's got line-of-sight to my location in San Francisco." The great thing about this story is both his terrific exposure to different parts of city and his willingness to share. It also makes it clear just how easy it is to set up a long distance link.
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Inspiring Adventures in SF Wireless Networking More

Inspiring Adventures in SF Wireless Networking

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  • Next time in town, I won't have to use a dialup!
  • Is it just me or have we been getting a lot of 802.11b stories lately? Maybe it's just to replace the lack of MS stories today:)

  • Slashdot effect makes 4m SF citizens impotent. (Score:5, Funny)

    by wackybrit ( 321117 ) on Wednesday May 29, 2002 @11:12PM (#3607250) Homepage Journal
    The link runs at 3.5 Mbps, which I barely make a dent in

    Now the whole of SF can experience the Slashdot effect, as 100,000 geeks point their 2.4Ghz transmitters at your aerial, creating enough radioactivity and EMG to render most of the male popular impotent.

  • Directory of WiFi (Score:3, Interesting)

    by NETHED ( 258016 ) on Wednesday May 29, 2002 @11:12PM (#3607251) Homepage
    I really wish someone would make a definitive database for WiFi locations based on either postings by users or the WiFi equipment owners themselves. I know that there are a few sites, but they, well suck. There needs to be a consentrated effort to do this. I'll gladly share my bandwidth if i know I can borrow someone elses later.

  • Haha! (Score:2, Funny)

    by Peridriga ( 308995 )
    I barely make a dent in


    With that kinda line of sight over San Fran and the entire population of Slashdot reading this... There will be a big dent soon

    Hope your connection is firewalled from your home PC('s) or there will be a dent in those soon too
    • He is running point to point with IPSEC at either end

      No dents for him!

    • Get it right! ping god.org Pinging god.org [204.181.30.186] with 32 bytes of data: Reply from 204.181.30.186: bytes=32 time=78ms TTL=235 Reply from 204.181.30.186: bytes=32 time=62ms TTL=235 Reply from 204.181.30.186: bytes=32 time=63ms TTL=235 Reply from 204.181.30.186: bytes=32 time=63ms TTL=235 Ping statistics for 204.181.30.186: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 62ms, Maximum = 78ms, Average = 66ms

  • 802.11b everywhere (Score:1, Interesting)

    by ajiva ( 156759 )
    I'm waiting for high speed 802.11b access to be everywhere. We should blanket the country with 802.11b, and just provide internet connectivity similar to cell phones. In your "area" you get internet connectivity for $x, if you leave your area it costs some $y. It would kill DSL and Cable, but it would be great for travelers, people too far from CO, etc

  • Grrr (Score:1, Interesting)

    by Anonymous Coward
    I really wish people wouldn't use generic acronyms in story titles. Especially when they use them for their less common meanings. "SF" on the internet generally means Science-Fiction, not San Francisco.

    I've noticed a rash of these in article titles on /. lately.
    • I don't know what kind of geekfest you're hanging out at on the Internet, but the generally accepted expansion of SF is San Francisco. It is also frequently used to abbreviate Sex Friend.

    • Re:Grrr (Score:3, Funny)

      by happyclam ( 564118 )
      I thought it was Single Female. Funny how "Science Fiction" never even crossed my mind when I saw SF. I thought "adventures in single female wireless networking" sounded pretty interesting...
  • Maybe it's just me, but this employer seems to be extremely cooperative. I wonder how much convincing he had to do in order to get this project off the ground.

    • Maybe it's just me, but this employer seems to be extremely cooperative. I wonder how much convincing he had to do in order to get this project off the ground.

      His employer has a wicked fast connection, presumably because he's in the same building as the ISP. From reading the article, I figured he's probably paying for a few megs of base usage that he isn't using right now. So his employee's project is "free".
      • And depending on what they do, he may be able to place it under "research" if they plan on doing more wireless links for their internal use/ or even for other employees...

        eg: If they give employees laptops w/ wireless cards and want to configure it so that the employees can seamlessly use the device both at home and at work......

    • Not too hard to argue if you are a large bandwidth provider like a large ISP. Bandwidth is typically purchased in bulk, meaning at any given point in time, a provider is nowhere near maximum capacity. 3.5 megs doesn't even make a dent in a few OC3s.

      In addition, it is a "perk of the job". No longer an employee, no longer free bandwidth. This is the problem with the community network designs relying on a few POP points to provide access...
      • Having worked for a private semi-large ISP. I can see how this wouldn't be a problem. There they are probably getting 100mbs for around $2000.00 mo. or, that is if they are a CLEC, (there are other charges for co-location etc.) but the bandwith just by itself is small, it's all the other stuff that makes the monthly charges go up.
  • That is a seriously nice view. Any house with a view like that near downtown SF must cost some serious bank, even when splitting the cost with roomates. Doesn't it?

  • Be thankful (Score:4, Funny)

    by inflex ( 123318 ) on Wednesday May 29, 2002 @11:45PM (#3607381) Homepage Journal
    I think this is great... out here in 'outback' Australia we're still trying to convince the budgies to comply with the Avarian packet methods.
  • I live on Potrero Hill, and can probably do line of sight to your house. I look at Twin Peaks out my living room window. Wanna try a linkup?
  • I will be living in Boston next year, probably in Alston or thereabouts. Anyone interested in getting Boston 'unwired' with me? Set up a few points throughout the city? I think it would be a great project to get most of the area for 4 miles south of the Charles to be wirelessly accessable to some of us!

  • ...to the beautiful lands down under? We'll be very happy to see you here!
  • Would anyone be interested in setting up a free wireless network in the North Side of Pittsburgh? I know that there is some wireless zone somewhere in downtown pittsburgh, but that's out of reach from where I am.

    Let me know if anyone is in the area, maybe we could get something going.

    You can message me here or email me at the above domain. Use my slashdot username @ domain. :-)

  • this must be the *real* golden age of wireless (Score:3, Interesting)

    by green pizza ( 159161 ) on Thursday May 30, 2002 @02:07AM (#3607696) Homepage
    The early days of radio sound pretty cool... imagine hearing about your neighbor "pulling music out of the air"! Or how about the first radio singers that "were paid to sing into a can [microphone]"?

    I grew up with radio and television... but my friends and I would still string up tincan-and-string communication systems and eventually started moding walkietalkies.

    These days the current generation of youngsters can transmit data at nearly half a megabyte per second with inexpensive electronics, a bit of coax, and a modified pringles can!

    Kinda funny how it all goes back to a can...

  • For your safety... (Score:5, Insightful)

    by isaac ( 2852 ) on Thursday May 30, 2002 @02:20AM (#3607730)
    For your own safety, and your employer's, you really need to install proper lightning arrestors on your outdoor antennas, or you could be in a world of hurt (and liability) if a fire starts in your house or your employer's building as a result of a strike.

    (I also question the wisdom of allowing outsiders on your employer's network, since you never know what kind of illegal activities the random users might be up to. Your employer says everything's cool, though so he's probably assumed this risk.)

    Just be careful.

    -Isaac

  • Where I live (West Texas) the town is flat. I live 3.3 miles from my office, but there are quite a few building between here and there. How line of sight is WiFi line of sight? Would I need to be able to see the building at the other end of the link?
    • If the building is concrete you will do okay, (standard brick) but if there's steel re-enforcement, forget it. Although I would still try, I have seen it defy all logic in one case. Is there a third point you could setup to relay off of that you can both see?

  • Scalability questions using 802.11b as a wan (Score:3, Interesting)

    by Indy1 ( 99447 ) on Thursday May 30, 2002 @02:30AM (#3607762)
    I know 802.11 was designed as a wireless drop in replacement /supplimant for traditional ethernet lan's. My question is, what happens if every house and business in America(world) throws up a WAP and a big dish on their roof forming one huge wan across the country. Can 802.11b scale this far (or big enough to handle a good size man - thats metropolitan area network for you non networking types) ? Is there enough bandwidth / frequency allocation in the 802.11 specs? What about packet collisions? Does the spread spectrum nature of 802.11 take care of this if the network was really huge?
    • The short answer is yes, but it would be incredibly hard to have every household. I'm sure there would be some places so dense that it couldn't be done too. You would have to have many cells of operation, using narrow beam antenna's both horizontal and verticle polarity and many many AP units. (For just one site) The big hangup on 802.11b is that there are 11 channels but only 3 of those channels do NOT overlap. So you have to be carefull how set it up.

  • Polarity of Antennas (Score:2, Insightful)

    by Anonymous Coward
    The waveguide is horizontally polarized, his grid antenna is vertically polarized. He should turn his grid 90 degrees, and reaim... Prolly start seeing a full 6mb (the real-world thoughput of wifi) over that link.

    • Re:Polarity of Antennas (Score:1, Insightful)

      by Anonymous Coward
      By gosh, you're right. And that amounts to about a 20 dB drop in gain -- pretty much negating the benefit of that $75 antenna. Ouch...
  • If your employer decides for whatever reason to discontinue the free connection, would it be possible to reconfigure it as an isolated LAN for the purposes of Q3A et al? I reckon that depends on latency and all that, and I haven't the inclination to look it up since I don't live in SF. (Though Wellington is in some respects similar...)

    Anyone already knowledgeable care to comment?

    • Re:If they pull the plug... (Score:1, Interesting)

      by Anonymous Coward
      yeah, we're already doing this out in toowoomba, australia - a bunch of smaller lans and home users are getting wireless antannas - mainly for games and file sharing.
      we'd like net access, but telstra would probably shoot us for sharing broadband and besides, how to share the cost?
      http://brismesh.org/ is brisbane which has a fairly established wireless network, and http://tolkun.com.au/mesh/ is toowoomba, which is just getting going.
      suprised slashdot hasn't done more stories on it.. it's a perfect environment for setting up a cute little *nix server :)
  • and ever time there is an earthquake (every 10 min it seems) hes gonna have to reposition his janx. :)
  • The Gist of the Following is that thou mayest need to reduce thy Power on thine Wireless if thy gettest too Effective with thy Antennae. (sorry, been reading Thomas Pynchon).

    By Tim Pozar - pozar@lns.com [mailto]
    for the Bay Area Wireless User Group [bawug.org]

    1. Background

      1. Introduction

        With the unlicensed use of 802.11b radio Ethernet devices in the Industrial, Scientific and Medical band that has been set aside for such use, there is confusion of what is allowed or limited by the Federal Communication Commissions Rules and Regulations. This paper is meant to help guide folks through the cryptic nature of these rules.

        This paper does not cover other legal issues of using these devices such as FCC type-acceptance, Radio Frequency Radiation issues (ie. ANSI RFR levels) or Appropiate Use Policies (AUPs) of ISPs you may connect to.

      2. What is the FCC's involvement in this mess?

        The FCC is a regulation body whose purpose was defined in the Communications Act of 1934 [fcc.gov] as:

        "For the purpose of regulating interstate and foreign commerce in communication by wire and radio so as to make available, so far as possible, to all the people of the United States a rapid, efficient, Nation-wide, and world-wide wire and radio communication service with adequate facilities at reasonable charges, for the purpose of the national defense, for the purpose of promoting safety of life and property through the use of wire and radio communications, and for the purpose of securing a more effective execution of this policy by centralizing authority heretofore granted by law to several agencies and by granting additional authority with respect to interstate and foreign commerce in wire and radio communication, there is created a commission to be known as the "Federal Communications Commission", which shall be constituted as hereinafter provided, and which shall execute and enforce the provisions of this chapter."

        The FCC, with the Act of 1934, was empowered to regulate wire and wireless communications. Wired communications regulation was needed to monitor and regulate monopolies. Wireless regulation is needed as the spectrum is finite. The FCC is the "traffic cop" to ensure that communications is not interfered with.

    2. Part 15 of the Rules and Regulations

      Almost every bit of spectrum is regulated by the FCC with the exception of extreamly high or low frequency spectrum and bands managed by the Intergovernmental Radio Advisory Committee (IRAC) for the military and other goverment orginizations, by licensing operators of radio equipment. The part of the FCC's rules that cover the operation of equipment that does not need a license is (3) Except as shown in paragraphs (b)(3) (i), (ii) and (iii) of this section, if transmitting antennas of directional gain greater than 6 dBi are used the peak output power from the intentional radiator shall be reduced below the stated values in paragraphs (b)(1) or (b)(2) of this section, as appropriate, by the amount in dB that the directional gain of the antenna exceeds 6 dBi.

      • (i) Systems operating in the 2400-2483.5 MHz band that are used exclusively for fixed, point-to-point operations may employ transmitting antennas with directional gain greater than 6 dBi provided the maximum peak output power of the intentional radiator is reduced by 1 dB for every 3 dB that the directional gain of the antenna exceeds 6 dBi."

    3. Lets dissect this section...

      • Part 15.247(b)(1) defines the maximum power that an intentional radiator can put out as 1 watt.

      • Part 15.247(b)(2) doesn't apply as it is covering devices in the 902-928 MHz band and 802.11b devices are in the 2400-2483.5 MHz band.

      • Part 15.247(b)(3) covers the need for limiting the amount of radiation the "intentional radiator" can emit with "directional gain" antennas. It says that in general (with an exception coming up) that if the gain of the antenna system is more than 6 dBi, the intentional radiator needs to be turned down to keep the emission at the 1 watt maximum plus 6 dBi (36 dBm or 4 watts EIRP). The FCC encorages the use of directional antennas [fcc.gov]. With that they give you 6 dBi more power for not poluting the rest of your space with radiation that is not needed to do what you need to do.

      • Part 15.247(b)(3)(i) covers the need for limiting the amount of radiation the "intentional radiator" can emit running "fixed, point-to-point" with "directional gain" antennas. This means that the transmitter is mounted not on a moblie device and is talking to one other transmitter.

    Do we need to turn down the transmitter?

    1. Omni-directional or Point to Multi-point paths...

      15.247(b)(3) makes the assumption that you are running a point to multi-point network much like an Apple Airport or Cisco/Aironet AP box with a number of computers connecting to the network. They may be randomly surrounding the access point so you are not using a directional antenna.

      But what does the FCC mean when they limit the "intentional radiator" to one watt?

      This is a critical sticking point in understanding what the FCC is talking about. There is some question of what an "intentional radiator" consists of and what and where exactly is 1 watt measured. Unfortunatly if you just look at these poorly written rules you will not understand what the FCC means here. One has to look a bit deeper to the "Report and Order" and Notice of Proposed Rulemaking" [fcc.gov] that generated this section of the rules.

      Things get a little clearer when we read this sentence in paragraph 4 of the Report and Order...

      • "The current regulations limit spread spectrum systems to a maximum peak transmitter output power of one watt. When operating at that power level, the maximum directional gain of the associated antenna may not exceed 6 dBi, resulting in a maximum equivalent isotropically radiated power (EIRP) of four watts, i.e., 6 dBW."
      With the old rules they are refering to the "intentional radiator" as a whole with a directional antenna can't exceed 6 dBw or 36 dBm and the antenna gain can't be more than 6 dBI. The transmitter can be up to one watt.

      In order to know if we are legal or if we need to turn down the transmitter we need to know the gain of your "intentional radiator". Let's say your access point actually puts out 1 watt of power and you want to put an omni-directiona antenna on it that has a gain of 5 dBi such as the ORiNOCO Range Extender Antenna" [wavelan.com].

      We know the gain of the antenna, the transmitter but we also need to know the loss of the transmission line going to the antenna as this attenuats the transmitter output power going into the antenna. Looking up the attenuation of a common coax cable such as RG-8 on an coax attenuation table [therfc.com] we find that at 2.4 GHz we have 16 dB of loss with 100 feet of cable. With a 10 foot cable your loss is about 1.6 dB. So your new "intentional radiator" will be radiating transmitter power output plus antenna gain minus coax loss or (30dBm + 5 dBi - 1.6 db) or 33.4 dBm or 2.2 watts EIRP.

      Since this is a non-directional antenna you are limited to 1 watt EIRP or 30 dBm. The transmitter will need to be turned down 3.4 dB to 26.6 dBm or about 0.45 watts (450 mW) to get you back to 30 dBm or 1 watt EIRP.

      If you think about this you may ask, "why add an omni-directional gain antenna it if I already was at 30 dBm?" You would be correct that it would be a waste of time. But if you had something like an Apple Airport that will only put out 15 dBm or 30 mW then you can add an omni-directional gain antenna and it will extend your "roaming" area. In fact you can add up to 15 dB of gain with an omni-directional antenna before you need to attenuate the output of the Wavelan card in the Airport.

    2. Use a directional antenna and get more power - or - this is where the Rules get even more hard to follow...

      Part 15.247(b)(3) actually gives you a free 6 dBi if you use a directional antenna your "intentional radiator". How do the do this? Only if the gain of the antenna is over 6 dBi will the Feds want you to roll back the EIRP of your "intentional radiator". You don't have to do it right at 1 watt EIRP. When would you do this? Say if you have an access point in the corner of a building and it needs to aim back into the work area. You don't want an omni-directional antenna as about 75% of the power would be going out the windows. Why not use a directional to keep the signal in the building and penetrate through the walls better? If we have antenna gain of about 12 dBi and in this case the antenna is a directional antenna. With the transmitter putting out 30 dBm and the coax has 1.6 dB of loss we have an "intentional radiator" that is putting out (30 dBm + 12 dBi - 1.6 dB) or 40.4 dBm or just over 10 watts EIRP. Since the antenna gain is 12 dBi and we have to reduce the power of this "intentional radiator" 1 db for every db we go over 6 dBi of the antenna we would have to roll the power back to 34.4 dBm or 2.2 watts EIRP (40.4 dBm - (12 dBi - 6 dBi)). Well, it is slightly better than 30 dBm or 1 watt EIRP.

    3. Fixed, point-to-point paths and get even more power...

      There is another exception to this section of the FCC rules. Part 15.247(b)(3)(i) covers systems that are "fixed, point-to-point". That means this path only has two transmitters involved and they are bolted down by never moving their locations. Automobiles may not apply. An example would be if you have an access point and a user that is a couple blocks or even tens of miles away that you want to connect to.

      This exception is more lenient as you only need to turn down the "intentional radiator" 1 dB for every 3 dB of signal over the 6 dBi of the antenna system. The FCC does this as it knows that these paths will not likely not be omni directional on each end and will have less of a chance to interfere with others as well as the need to span some long distances.

      Lets look at an example using the same antenna, transmission line and transmitter as above. Without turning anything down we had an "intentional radiator" that was producing 40 dBm or 10 watts EIRP. Since the antenna gain is 12 dBi and we have to reduce the power of this "intentional radiator" 1 db for every 3 db we go over 6 dBi of antenna gain we would have to roll the power back to 38.4 dBm or 7 watts EIRP (40.4 - (12 dBi - 6 dBi) / 3).

    Real world examples...

    1. Omnidirectional Point-to-Multi-point...

    2. Directional Point-to-Multi-point...

    3. Directional Fixed, Point-to-Point...

      Recently I put up a short path between myself and a neighbor about 2 blocks away (.2 miles). I have an Apple Airport that uses the Lucent Wavelan Silver card that puts out 30 mW or about 15 dBm. The antennas have a gain of 24 dBi with a transmission line loss of about 6 db. This gives me an "intentional radiator" power of 48 dBi. Since the antenna gain is 18 dBi over the 6 dBi that the FCC gives you and since it is a fixed, point-to-point link I would have to limit my

      [...]

      Since the little Wavelan card only puts out 15 dBm, I am legal as far as part 15.247 goes.

    Quicky Definitions...

    1. deciBels - dB

      dB, or one tenth of a Bel, is a unit of mesurment that looks at the ratio of one value to another. Gain or loss can be measured in dB. The dB scale is an exponential scale using the formula log(ratio)*10. This means that 3 dB is about twice the power, 10 dB is 10 times the power, 13 dB is about 20 times the power and 20 dB is 100 times the power.

    2. dBm

      dBm is deciBels referenced to a value of 1 miliWatt of power. Power over or under 1mW would be plus or minus dBm respectively.

      If you have a transmitter that produces 1 watt of power that would be 1000 times more than 1 mW so that converts to 30 dBm.

    3. dBW

      dBW is deciBels referenced to a value of 1 Watt of power. Power over or under 1 Watt would be plus or minus dBW respectively.

    4. Effective Isotropic Radiated Power - EIRP

      Effective Isotropic Radiated Power defines the gain of an antenna over an "isotropic antenna" that would radiate equally in all directions.

      An example would be a light bulb. A lightbulb is designed to radiate light equally well in all directions, except the direction that the base is in.

      If you have an antenna that radiates better in one direction than another, it would likely have gain in this direction. The amount of gain would be shown as "dBi" or dB gain (or loss) over an "isotropic antenna".

      To further our example above, if we have a light bulb and put it in front of a mirror, we would be taking the light radiation that would be heading in the direction of the mirror and reflecting it back in the same direction of the light not directed towards the mirror. Hence you would have twice the amount of light going in the direction of the refelction. As we are doubling the amount of light, we have a "gain" of 3dB or 3dBi.

  • 802.11 risks (Score:4, Interesting)

    by Wise Dragon ( 71071 ) on Thursday May 30, 2002 @09:21AM (#3609083) Homepage
    This is from an article [weblogger.com] on 802.11b.weblogger.com. The gist of is that licensed users of the 2.4Ghz spectrum are allowed to radiate at up to 1.5kw, effectively shutting down 802.11!

    [Dewayne] Hendricks [of the FCC] pointed out a simple case in which hams could shut down an extensive area. "Ham television is becoming more and more popular, the equipment's becoming cheaper; lots of hams like to broadcast," Hendricks said. "It's a pretty sexy application."

    Hendricks said that the San Francisco Bay Area already has a number of ham TV repeaters. "A bunch of hams could deploy TV broadcasts" up to 1.5 kilowatts (kW). "We could effectively shut down 802.11 in the entire Bay Area, and it would be perfectly legal and there wouldn't be anything you could do about it." Part 15 devices like Wi-Fi radios are limited to less than 1 watt (W), and many devices use 30 to 100 milliwatts (mW). (When you start talking about radiated power output, these numbers are only starting points for calculations.)

    • While Hams may have a maximum power output at those frequencies, broadcasting at full-blast is not necessarily legal. I can't remember exacty wording, but I think the phrase "mimimum necessary power for effective communcation."

      While a Ham might make a case for using a given power level, it might not always be legal.

      -Signed, former Ham

    • Re:802.11 risks (Score:2, Informative)

      by pozar ( 54229 )
      If you want to see what the risks are to 802.11, check out my paper at:

      http://www.lns.com/papers/part15/Regulations_Affec ting_802_11.pdf [lns.com]

      It covers everything from co-users (interference)to Radio Frequency Radiation to human tissue, to antenna height and equipment certification.

  • I was going to ask the boss for a cable connection for our SF 'office' (really a Tenderloin apartment...)
    now i've got a(nother) decent option! I love it! :)
  • With the priciness of getting space on a tower I started thinking about how practical it would be to use helium ballons as repeater antenas. Has anyone else looked into this? I know weather stations send up ballons twice a day but I wonder what kind of FAA regulations you would have to wory about to get something like this going.

  • Crackdown by ISPs (Score:4, Insightful)

    by bluegreenone ( 526698 ) on Thursday May 30, 2002 @12:25PM (#3610444) Homepage
    One thing I'm surprised that doesn't get mentioned more is the expected response of ISPs to people re-distributing their bandwidth to strangers via wireless. As this becomes more common I think you can count on telecos at the very least preventing customers from sharing bandwidth with the general public with their service agreements. The more people that share a connection the fewer customers telecos will have. Imagine the response from a cable company if someone started sharing their cable TV via wireless!

    Expect a response soon from the big ISPs. Wireless is currently in the phase that MP3 sharing was in its infancy, too small a blip to register much. But it will attract attention as more people do this. I wouldn't be surprised to see them even getting laws or FCC regulations that prevent wireless sharing.

  • Is this legal? (Score:4, Informative)

    by Skuld-Chan ( 302449 ) on Thursday May 30, 2002 @12:30PM (#3610483)
    Under part 15 you're only allowed 6db of gain - this guy is running two 24db grid style parabolic dishes.
    • Legal? Not sure - depends on other factors as well which aren't necessarily in the article. Chances are, he's ok, but he's never made indication of what his calculations are. Also, the FCC has been beating on people (WISPs) more for using untested (uncertified by FCC) combinations of equipment - which is easier to prove in court than overradiated power.

      6dB? Where does it say that? And where relating to a point-to-point link? The ratings are ERP (effective Radiated Power) in which the dB rating of the antenna is a single factor.

      Other things include the loss of the cable, the connectors, the power output by the device itself, etc. I suggest you get your butt over to http://www.access.gpo.gov/nara/cfr/waisidx_98/47cf r15_98.html and try reading the regulations.

      Check http://www.austinwireless.net/index.cgi/FreqentlyA skedQuestions#line83 for some more info on this, including a link to the above gpo site.

      And I think the above pertains to point to multipoint links, which have different regulations than point-to-point links on wireless.

      • Your allowed more for bridging. Including power output, can output up to 2 watts for a bridge, but only 100 mw for AP units.
      • 6dB? Where does it say that?

        Right here [gpo.gov]

        Keeping in mind that there's no real actual clear definition in the spread spectrum rules in Part 15. It does give a statement that monitor input may not exceed 6db.

        I do have an amateur radio license so I'm not an RF idiot - and they do require you to calculate erp in the extra class exam (which I passed). Your right - feedline loss, antenna db, and transmitter power make a big difference in erp - especially feedline. For 2.4 ghz I'd never use anything less then something with an aluminum jacket.

    • Re:Is this legal? (Score:2, Informative)

      by pozar ( 54229 )
      He is allowed any gain of antenna he wants. He just has to back off on his transmitter power (1W and down) depending if his antenna has more than 6 dBi of gain and if he is running point-to-point or point-to-multipoint.

      See my paper at:
      http://www.lns.com/papers/part15 [lns.com]
      for details on FCC Part 15.247.

  • It looks like the placement of your antenna is perfectly in the way of several pipes. And those pipes I'd hazard to guess are Fire Department lines for emergency. If that's true, you've got a beautiful lawsuit just waiting to happen. And thousands of witnesses to say "yeah, they had wires and pipes and stuff cluttering up the roof there" from Slashdot.

    If they ARE NOT fire pipes, then you'll just tick off the building management (And I'm an alarmist). If they are, I'd have to think you're being irresponsible in your placement (and I'm not an alarmist).

    I can appreciate the wireless link you did, it's cool. Good luck and hopefully nobody will blast on your channel nearby. :)

  • There is this company called Biongo brought to by the proud of owners of Earthlink formly known as Mindspring. Biongo has 3hotspots in the seattle area which is all located by the sea-tac airport. PRICKS.
  • I saw this stuff at the NAB convention. Looked really good and not that expensive.. Here is the literature and prices you requested for the Trango Microwave Systems. www.trangosys.com Falcon Plus 5.8 Ghz - 1 mile system - $ 2250.00 Falcon Plus 5.8 Ghz - 4 mile system - $ 2749.00 Falcon Plus 5.8 Ghz - 7 mile system - $ 2849.00 Eagle Plus 2.4 Ghz - 1 mile system - $ 1168.00 Eagle Plus 2.4 Ghz - 4 mile system - $ 1408.00 Complete systems include: transmitter and receiver, transmit and receive antenna suitable for distance, all weather nema enclosures, hardware, antenna to radio cable, power supplies, manual. Resellar pricing is also available. Thanks Aaron Davis Diversified Marketing 509-585-9377 Phone 509-585-9455 FAX
  • I've heard of a five mile Non-Line-Of-Sight Network between a rich kid and all his friends. Has anyone heard of a cheap version of this?

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