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Using an Old Satellite Dish as a WLAN Antenna
=m8s=Dark Underlord writes "I was browsing for wireless stuff and came across this link that shows how to use an old satellite dish as an 802.11 antenna." The directions tout the range as being 10 miles given line of sight. We've had other stories about building antennas, but I think these are cooler because of their focused nature, but a Primestar dish is a little tougher to locate than a Pringles can or a floppy disk.
The Original Slashdot Article
Looks like you can pick up a Primestar dish on eBay for about 50 bucks (current auctions here). Shipping looks to be about $20. Anybody know of other sources for acquiring these dishes?
.sig
I tried this a while back, but at the time, even unused sattelite dishes were too expensive. I borrowed a neighbors' dish for the experiment. The hard part was focusing the dish - If you didn't have something sturfy to mount it to, then you would lose the signal pretty easily.
Why bother with the Primestar dish for $50 on Ebay when you can get a real 802.11b/g antenna with 24dB gain for about $65? If memory serves, every 3dB is double, so 24dB is 2^8 or 256 times the signal strength.
Primestar was purchased by Directv, who made the old primestar dishes "useless". Directv sent new satellite dishes and receivers to anyone who was subscribing to primestar.
Google Cached Version
http://216.239.53.104/search?q=cache:ltX22XDG3_4J: www.wwc.edu/~frohro/Airport/Primestar/Primestar.ht ml+&hl=en&ie=UTF-8
Hey, guys, this would violate FCC part 15 and other applicable rules. Specifically, we are referring to ERP (effective radiated power).
Have fun if you get nailed!
If you are interested in this, check out the Canteena solution which has a 12 db gain. You can get a *new* shiny antenna for much less than the cost of a used Primestar dish on EBAY. I know the dish in the article boasts 22 db gain with a 10 mile range but, keep in mind that setting up communication that is line of site 10 miles apart is nearly impossible. (Just try using a camera with an 8x telephoto lens to take a non blurry picture, you'll start to get the idea. ) Have fun!
Theres even a 50 foot homemade dish for ham radio. Build your own big dish
My dish network is not fixed, and has been working for over a year. I use an old carpet to prevent sliding, and place it against a wall on the side and a box on the back. It has been surving 35mph winds.
The hard part is pointing it, but once getting it right it is easy to replace it in position.
Did you ever think to RTFA...
"A Primestar dish. (You may use any old dish, but if it is bigger than the Primestar the gain will be higher, and it may not be within the Federal Communications Commission rules for use within the United States. In fact I have come to find out that there seem to be several different dishes that Primestar used, and I am only sure that the one I used, pictured above, used with the ordinary Wavelan or Airport transceiver card is within the effective radiated power limits given by the FCC.)"
Actually... with equipment that will use loose timing 30 miles would be no problem. You could even use an omni on the other end.
The main problem with these is getting them high enough for line of sight and also mounted sturdy enough. Mountain to mountain is the best for these kind of links.
With a beamwidth of 1degree or less those 6-10ft dishes have to be held dead still or you loose your signal at any distance.
Anyways.. the record is something like 120+km with two of these things and some VERY modified radios in the cards.
Telcos have alot of dark fibre in the States. Most people assume that's optical fibre...but it's actually moral fibre.
"I sacrificed a db of gain here by not turning it over, mostly because I'm mounting it on a vent pipe, and didn't want to put that kind of wind load on it. As mentioned above I don't really need the extra signal either."
Wonder if he realizes what that vent pipe is for? Are there any studies on the interference factor from 'methane gas' emmisions on WI-FI?
Maybe it's just the bathtub/sink vent.
sig mind freed
The atmosphere is opaque to ham radio frequency and so the signal bounces back to earth (that's why you get different levels of signal quality depending on the weather, etc.) while the atmosphere is transparent to the Ghz frequency of Wi-Fi so your signal goes off into space.
Ok I understand the curvature of the Earth thing. But damnit! HAM Radios don't have to be line of site. Why the hell do I have to be within line of site of my friends house to reach his bandwidth!
I'm not sure if you're kidding or not, but I'll tell you the reason anyway.
It has a little to do with output power, but mostly to do with frequency. The higher in frequency you go the more readily the energy is absorbed by "stuff."
Ham operators use HF frequencies (loosely defined as about 7MHz - 30MHz). Those frequencies tend to be reflected and/or refracted by the atmosphere and they can "skip" over great distances. Once the signals reach the ground, they can bounce off the ground and skip again, leading to VERY great distances. If the atmosphere didn't help in this way, ham operators would too be limited to line-of-sight.
All opinions presented here aren't mine.
There are much better solutions. While a pringles can and cantenna might work, assumng you put it right in the focal point, build the cantenna right, and can find the dish, this might be a better way to go:
Try this.
Its a 24dB gain antenna (Thats 256 times power folks), its guaranteed to work, it HAS a feedhorn, and all the calculations have been done for you. Not only that, its a grid antenna so there is almost no wind loading. You might pay 50bux or more for a primestar dish on ebay, plus trying to get the can into the focal point, etc. There is certainly a certain apeal in doing it yourself, but sometimes work for the sake of work is no fun at all.
The best thing? Its only 70 bux, WITH the feedhorn and pigtail.
Right now im using one of those, and two 10 foot C-band dishes to make a big triangle network connection. The C-band to C-band dish connection is over 30km long. (Yea I'm in Canada: 30 kilometers = 18.6411358 miles)
It's easier to fight for one's principles than to live up to them.
For what it's worth, two Linksys WAP11's in bridge mode, and two directional 24dBi gain antennae, and my link is rock solid at 1.1 miles.
I use Linksys WET11 bridges with 24dBi grid antennas made for 2.4GHz (also less than $70 each) and have a rock-solid 11Mbps link a bit over 6 miles away. The trick is to mount your WET11 in a weatherproof box right underneath the antenna, to keep the coax pigtail as short as possible, because signal loss in a long coax is the distance killer. I have only a 3 foot long coax pigtail and run the dc power up the unused pairs of the CAT5 cable to power the WET11. You may have a significant voltage drop at the end of a long CAT5 cable, so you may need to use a +6V or even a +7V DC power supply of adequate amperage to ensure that you still have +5V DC at the end of the CAT5 cable with the WET11 plugged in loading it down. I had to use a +6V, 1.5 amp DC power supply on mine to keep the voltage at +5 volts at the end of my CAT5 cables, or the WET11 wouldn't run.
Only the party obtaining the FCC certification is allowed to specify another antenna. You, the user, cannot alter the device even if it meets the requirements of 15.247. Modifying approved transmitters is generally not allowed, with the notable exception of the Amateur Radio Service. A new configuration with higher antenna gain requires a new certification. 47CFR2:
[emphasis added]So unless you have the money to spend on a complete recertification (it's neither cheap nor easy), leave your wifi alone!
Read ALL the regulations, starting with Part 2. The technical limits in Part 15 apply to the "responisble party" who obtains the FCC certification. It has nothing to do with user antenna modifications, which are expressly forbidden by the regulations. Any user modification is forbidden, except for Part 97 use (amateur radio)-- and amateur radio cannot be legally used for public wifi setups.
According to the Cisco distance calculator you need a pair of ~169' towers to do a 32.7 mile links using their 21Dbi dishes. So no mountains needed, but you WOULD need a flashing light at the top and certain permits as I believe anything over 150' needs to have an FAA clearance so planes don't crash into it =)
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
How the heck do you sight something like this in? You have to be accurate within a few seconds, don't you? A search pattern would take forever with that narrow of a beam, wouldn't it?
The beam isn't that narrow. Let's do a quick mental calculation. A typical direct-to-home Ku-band dish is going to have a beamwidth of about 1 degree (2 degrees, whatever) in order to be able to isolate the right satellite on the arc. That's at Ku-down, which is about 11 GHz. A given antenna will get "wider" as you go down in frequency, so the beam width at 2.4 GHz for this same antenna is much wider. I believe the beam width and frequency scale inversely, so if you go down in frequency by about a factor of 5 (11/2.4) then your beamwidth (however you want to measure it) goes up by the same factor.
So your beamwidth at 2.4 GHz is going to be something like 5-10 degrees. And it's not a super sharp rolloff, so you'll find that signal easy.
Another way of expressing all of the above is to say that an antenna with a certain gain at a high frequency (like Ku band) is going to have a lower gain at a lower frequency, and the corollary of that gain reduction is lobe spreading.
Hey, maybe someone here can point us to a visualization tool for this -- looking at an antenna pattern for a given antenna, crank down the frequency and watch the lobes spread out and drop.
One simple rule for its versus it's
The FCC doesn't seem to care much about power levels and antennas in the ISM band. Remember, it's kind of a throwback "freebie" given to appease the anarchist crypto parasites and cheap low end consumer equipment for those unable to afford the "protected and scarce" high dollar bands that go up for auction. :-)
The only exception might be certain commercial product vendors who try and sell out of spec equipment to the masses. That is actually worth their time, but some guy with a primestar dish? no way. [ Like linksys getting pressured to take their 2.4Ghz amps off the market because they could interoperate with too many other "unapproved" equipment configurations. Supposedly they can sell them again after making them harder to use with anything but linksys/cisco. arg. ]
There are a number of smaller WISP's that I've come across in the northwest that run 1/2W and 1W amps on their directional point-to-point and point-to-multipoint configurations, but until someone complains that they are interfering, there is no way the FCC is going to proactively come out and bitch.
Wireless users groups across the nation post plans and site configurations using all sorts of unapproved antennas, radios, amplifiers, etc. There is no widespread FCC CRACKDOWN going on. In fact, I challenge anyone to name an incident where a WiFi user (not company) was pressured or forced by the FCC to alter their equipment back into spec. It doesn't happen.
Personally I think this is a good thing. The FCC has done more harm in the 802.11 space than good. Like antenna connectors. Do you know why there is a proliferation of SMA, RP-SMA, N-type, BNC, RP-BNC, MMCX, and any number of other bastardized formats for antennas and equipment? The FCC requires vendors to make their radio's use proprietary connectors to prevent people from easily and usefully extending the range of their equipment with generic antennas. Not that the vendors mind. Nothing like vendor only parts with the associated 400% markup to pad the profit line.
Let the FCC play with the Big Co's and handle licensed spectrum. The ISM bands are where its at.
I've got a reasonably fool proof way of making use of these offset dishes, unless of course you're the more talented fool. The Australian Fox TV dishes are similar, but lend themselves to this technique. Aquire some mirrored perspex or something similar. Cut it into small squares, or just steal a mirrorball. Randomly cover the surface of the dish with these using double sided tape. The thinnner the tape, the better. When you reckon you've got enough, point your dish at the sun so that the focal point, your tin can feed or quad, helical whatever is glowing quite well. Too many little mirrors and you'll melt it. All you want is to be certain that the focal point is exactly where it needs to go. Right on the signal feed. If you know where the feed point is, you also know where the sun is. A pointer of some kind pointing directly into the sun, fixed to the dish so that it throws as little shadow as possible can be used to accurately align the dish with little effort. Mount the dish on your roof. sight along your pointer at the source of the signal. Voila. Dish aligned. Jaycar in Australia sell sheets of tiny mirror squares that are perfect for this job. http://www.freenet-antennas.com in WA has managed some big distances with a modified dish. He doesn't use my alignment method thow.
Some links:
KI7cx dish
Primestar dish
Bi-Quad feed for primestar DIY
10 Euro dish with biquad feed
Modifying Confier Antennas for Wireless Networking
More info: Wireless Leiden
More info about the ARRLs take on that:here. They point out that channels 1-6 fall within the amateur band around 2.4 GHz, and if they get modified within the part 97 allowances for amateurs they could use them instead of the slower packet radio (although I have read about 5-10Mb/s links, but they are more for backbones between the slower areas).
So yes it is posible, just remember that you can't encode/encrypt to obscure the meaning of the data. (Although I have never read anything about putting a passowrd, you might run into trouble because some OSes (i.e. Windows 95B & later ) encrypt the password before sending it).