How-To: Build a WiFi biquad dish antenna
posted November 15th 2005 2:45PM
Wireless enthusiasts have been repurposing satellite dishes for a couple years now. This summer the longest link ever was established over 125 miles using old 12 foot and 10 foot satellite dishes. A dish that big is usually overkill for most people and modern mini-dishes work just as well. The dish helps focus the radio waves onto a directional antenna feed. We're building a biquad antenna feed because it offers very good performance and is pretty forgiving when it comes to assembly errors. Follow along as we assemble the feed, attach it to a DirecTV dish and test out its performance.
Why? With just a handful of cheap parts, a salvaged DirecTV dish and a little soldering, we were able to detect access points from over 8 miles away. Using consumer WiFi gear we picked up over 18 APs in an area with only 1 house per square mile.
Building the antenna
Biquad antennas can be built from common materials, which is nice because you don't have to scrounge around for the perfectly-sized soup can. We did have to buy some specialized parts before getting started though.
The most important part here is the small silver panel mount N-connector in the center of the picture; the entire antenna will be built on this. We purchased it from S.M. Electronics, part# 1113-000-N331-011. The "N-connector" is standard across the majority of commercial antennas and you can connect them to your wireless devices using "pigtails." The longer pigtail in the picture is a RP-TNC to N-Male pigtail that we'll use to connect our antenna to a Linksys WRT54G access point. The short pigtail is a RP-MMCX to N-Male pigtail so we can connect to our Senao 2511CD PLUS EXT2 WiFi card which is pictured. We also purchased 10 feet of WBC 400 coax cable so we wouldn't have to sit with the dish in our lap. We got our surplus DirecTV dish from Freecycle. We'll cover the reason for the mini butane torch later.
Trevor Marshall built one of the first biquad WiFi antennas found on the internet. We followed the slightly more thorough instructions found at martybugs.net. Here are the raw materials we started with:
The wire is standard solid-core 3-conductor wire used for most house wiring. We didn't have any copper printed circuit board material laying around so we used this thin sheet of copper and supported it using the 1/4-inch thick black plastic pictured.
The first step in building the element was stripping and cutting a 244mm length of wire.
We marked the wire every 31mm with a permanent marker and began bending the wire into a double diamond shape. We tried to make the length of each leg 30.5mm.
The easiest way to make really sharp bends in the solid copper wire is to use two pairs of pliers. With the pliers held perpendicular to each other bend the wire against one of the sets of jaws.
The element with all bends completed:
Next we cut out a 110mm square of black plastic to use as a base for the reflector. We drilled a hole in the center to clear our connector.
We then soldered a piece of copper wire to the center pin of our N-connector.
Next we soldered a piece of of wire to the outside of the connector. We ran into some trouble here. Our cheapy iron was not capable of getting the connector's base hot enough to make a good solder joint. We bought a butane torch and used that to heat up the surfaces. This worked pretty well except it desoldered our center pin. We recommend you solder the outside piece of wire first before doing the center one.
After the connector had cooled it was attached to the black plastic base using epoxy. The thin copper sheet was attached to the front with epoxy and trimmed to fit.
We let the epoxy cure for a while before proceeding. The next step was to solder our bow tie shaped element to the vertical wires. The element was supported by two pieces of scrap copper trimmed to 15mm to ensure proper positioning.
Then the extra wire was trimmed off and the outside wire was soldered to the ground plane to complete the antenna.
To make mounting to the dish easy we modified the original feedhorn. Here is what it originally looked like.
After removing the housing, internal components and shortening the feedhorn looked like this.
The antenna is attached by inserting the N-connector into the tube and then connecting the coax cable.
Here is a picture of the final antenna assembly ready to be attached to the dish.
Since the satellite dish has an off-center feed it looks like it is pointed at the ground when it is level with the horizon. Even though there are no angle markings for setting the dish at 0 degrees inclination we can still ensure that the dish is pointing at the horizon by setting the dish angle to 45 degrees and mounting it on a tube with a 45 degree angle.
Test results
The Engadget Corn Belt Testing Facility has broadband access provided by a local WISP. So we knew if we plugged in our antenna we were sure to pick up something in the area. We pointed the dish at the closest grain elevator, where the WISP mounts their antennas. We connected the dish feed to our Senao card and started up Kismet.
We expected to get one AP, but five is even better. Looking through the info strings we were able to determine where the APs were since the WISP had named them according to the town they are in. The AP on channel 5 is the one we pointed at in town A, 2.4 miles away. The AP on channel 6 is located in town B, 8.2 miles away. The two APs on channel 1 are a bridge between town A and town C which is located 2.6 miles directly behind the dish.
Our next test was to hook our WRT54G up to the dish and point it at a hill 1 mile away. We drove to the top of the hill and used an omnidirectional mini whip antenna with our Senao card to detect it.
Our router was picked up easily. The found 14 other WISP APs including town D, 7.8 miles away. The WISP is definitely using some high powered equipment if we're just picking this up with an omnidirectional antenna.
For a final test we put the dish on the roof rack and parked on top of the hill to see if we could pick up any more APs.
Our final count is 18 APs, 17 of those belonging to the WISP. This was a pretty fun project and shows that you can build decent wireless solutions using consumer gear.
For the curious: The WISP gives its subscribers a patch antenna with a built in power-over-ethernet access point. Once the antenna is mounted to the roof they run a single ethernet cable into the house which means they don't have to worry about signal loss from coax. These client boxes are manufactured by Tranzeo.
lotfi
This. Is. Awesome.
I think this is the perfect replacement for the Cantenna. I already have a spare DirecTV dish gathering dust, so why not use it?
I would like to know wtf is happening with this site that i´ve not seen neither loaded the images all times i access in. Is it a problem from me or anywhere else? Thanks.
The images don't load for me either. This is a great project. Can you please fix the images?
Thanks!
Actually, an RP-MMCX to N-Male pigtail will not fit a Senao card, as Senao connectors are not Reverse Polarity, they're standard MMCX. The SMC2532W-B do have RP-MMCX connectors though.
Looks great!
According to the loss stats on the coax's data sheet though, you'll lose almost a whopping 7 dbi of gain over 100 feet of cable....
I wonder how it would work as a roof antenna if you ran hardline? Awesome, I bet.
Although, this could be useful with the previous router in an outdoor box post. In fact, it's perfect!
Oh, P.S. for all the people who might want to build one of these, and aren't too familiar with RF coax:
RF coax is not the same as your normal CATV/satellite coax. You can't use SAT coax! You'll damage your gear.
CATV/SAT coax is rated at 75 Ohms of impedance. RF gear requires 50 Ohm cable... Some Radio Shacks still carry it... but places like Home Depot don't.
Just be careful or you'll damage your gear.
If you use this antenna in your house you could get into most of the wireless networks in your neighborhood, right?
Does it mean that you no longer need to walk down the street with your Cantenna to find a network?
am I wrong?
You are right! :) Start building yours! Hehehe.
MElias:
You couldn't use it *inside* your house and get effective coverage... your walls will eat any signals from far away.
You'll get best results if you stick it high up outside. The higher the better.
there is a faint wifi that i get only when i stand in my front yard, so if i get this then i will be able to use the wifi fine inside my house?
hat do u need this 4?
Sultan, you should brush up on your basic antenna theory if you think a dongle attached to the dish will have anything near the performance of a bicubic quad antenna.
Allow me to recommend:
The ARRL Antenna Book (click my name for the direct link)
whats rather disturbing about this vs the cantenna is its not obvious what you are doing...if i see someone walking around with a cantenna or see one sticking out of the side of their house i know exactly that they are stealing my wifi and/or attempting my computers...This dish is great because the police wont know the difference and neither will i but its kindof disturbing to realize that it is getting easier and easier to steal other peoples internet that people like me pay for.
What is worse is that people are getting busted for downloading things on p2p networks and bittorrent sites and they only bust them by ip address...how can you get caught if your stealing your neighbors internet from a few blocks away? I wonder how they will deal with this issue in court.
More about dish antennas here:
http://wireless.binarywolf.com/parabolic.htm
Are both wires from N connector soldered to double diamond or is the outside wire connected the big copper sheet?
If there was some way to work this into an active dish that's getting satellite tv, I'd be sold on it. Can't see mounting 2 dishes on my house hehe
There are many variations of this type of antenna out on the web. One resource is: http://www.wikarekare.org/
My favorite is the bicircle:
http://www.wikarekare.org/Antenna/bicircle.html
I've build a couple for 802.11b/g using large gauge #6 bare ground wire from Lowes and 6x4 inch 16oz. copper sheet metal from a local sheet metal shop (you might look around for a rain gutter shop... they use similar stuff).
By recalculating the specs you can build one for cell phone boosting (both GSM and CDMA single and dual band).
I currently have one dual-band design on a rooftop mast that pulls in cell signals from miles away. In this case its used for CDMA EVDO access in a mountainous area that normally receives no signal. :)
i live in a rural area in indiana. There is a WISP about 8 miles from my house and they say that they only serve a 3 mile radius. So, I could get an account with them even though im too far away and build one of these to connect to them? I am very interested in this because the only high speed available to me is sattelite and it sucks. Also, will this only work to pick up Wireless ISP's or can you pick up regular old wifi routers as my buddy is about 7 miles away with a linksys wifi router on roadrunner. Plz help, this could make my year to get off this damn sattelite.
FYI, when using a biquad as a feed on such a dish, you should make the reflector 110x110mm (while 123x123 is better as a standalone antenna), and add some side lobes to it to reduce radiation from the rear lobes.
Also be sure to check your local regulations, as a biquad-fed dish is likely to exceed any local maximum EIRP limits...
So approx how much do all the parts cost to build this thing.
Will this work after the copper bowtie turns a pretty shade of petina?
hey we were wondering if you needed line of site...
habitual,
yes this will work perfectly. It might be even possible to use the same bi-quad but simply put it in a sardin can.
If you need a picture of something simple just mail me at info@linkpixels.com
Cheers,
Ries
Satellite dishes hooked into laptops, bolted on the top of a Subaru? This is the ultimate in geek-chic! I must make me one of these.
I oft find myself needing internet @ a friends house in the projects but I can only find one unsecured AP in the dinky range of my built in WiFi.
This page is soooooo getting bookmarked.
1 watch the leignth of your coax every 3db of loss is half your power to your antenna
2 there are LIMITS to the power your allowed to put out by the FCC to protect licensed services (large fines)
3 they dont use just your ip to get ppl for downloading they use a unique hardware address embedded in a persons net card wired and wireless called a mac address every nic has one of its own no two are the same
#26 - the mac address can easily be spoofed. as well as that, you can't get a mac address over the internet, only from the local network. it's not true that they can bust you from mac address. maybe for stealing their network through mac address, so i suggest you should spoof it.
About dB loss, if you are really concerned about losing the signal I suggest that you purchase a wireless router (one that can connect an external antenna, preferably two antennas, such as a linksys etc) then place your router in a weatherproof box as close to the antenna as you care for. Then you simply run an ethernet (Cat5E or Cat6) cable to your switch etc and your done, minimal loss of dB.
Of course sometimes that loss can be benificial say if for example you're exceeding your legal output dB, then losing a little in the cabling can drop it down just enough.
--Praetorian_TMOTC
Very cool, I'll have to give this a shot. I wonder if I can use a home built dish (made of mesh) and not a TV dish.
I am adding a link to satellite dishes on eBay for anyone who is interested in building one of these.
check this out - reasonable results with usb dongle http://www.usbwifi.orcon.net.nz/
and this too for everything diy wifi
www.manuka.orcon.net.nz
and this too for everything diy wifi
www.manuka.orcon.net.nz
Ok lets say i made this setup ok.Now how do i check if i have any connection to my dish?
And does it have to be this card http://www.wlanparts.com/product/NL2511CDPLUSEXT2
I can imagine a much better geek toy with the came concept: a rotating/oscilating RADAR dish used to search for wifi :) . Bonus points if you can get it to track to 2.4ghz signal sources, and doubly so if it can track 2.4ghz while discerning between wifi and home phones.
Oh god, now I really want one. But first I'll need to justify getting a car... :)
gots a question im roughley 20 miles (give or take) from a collage in southeren illinois i have a large antana and it is all flat land with a minimum of trees, buildings, ect we are suffering with dial up and i am realy starting to get interested in wireless is there any way for me a novice/newbe to hit a hotspot that far away and if so directions or a website would be great
I have an old 20" dish lying around and I need some more info before I go ahead and try this.
First, is there any way to buy the feedhorn for this type of thing? I don't trust my handyman skills all that much.
Second, I like the idea of sticking the router right up there with the dish. I know the router sends out signal, but will it actually receive it from the antenna? Basically we're talking about inverting the functions of a wireless router- using the antenna to receive and the ports to send out the connection. If I wanted to repeat the wireless signal, I presume I would need 2 Wifi routers?
38 try two pf thes hooked tigether in a Phased array (google phased array)
39 a router is a 2 way device to your CARD and back if you get a linksys wrt54g then you can setup 1 tranciever port(antenna connector) to the biquad 1 to an omni and setup 3rd party firmware i sugguest http://www.sveasoft.com/
im not affiliated with them but i do like their feature set also this design is very forgiving also try finding a hamfest in your area they have all kinds of antennas even commercialy made 2.4ghz antennas and yes that is the frequency we are working with
how would i go about using this configuration to boost a cell phone signal....
how would i go about using this configuration to boost a cell phone signal....
How much do you shorten the feed horn?
thanks
jb
How much do you shorten the feed horn?
thanks
jb
Hey Guys. WOW that all is so cool... teehehehe Tracking the signal. Yeah sure, I can do that. Hope everything works out for ya. So Great ideas. U have helped me soo much. now i no what to do with my dish. i was going to make a bird barth... hahaha
jeremiah kb9vgr:
How do you keep your router from broadcasting back on the 14db antenna all over the neighborhood? I'd like to receive on the biquad and broadcast on the low gain
antenna(s) included with the router... I guess it doesn't matter since my network is secured but isn't 14db a pretty strong signal? I wouldn't want to create too much interference.
Thx,
~ n8
That's very cool but, there are 4 images i cannot see... the first one, second, ninth and twelfth...
i'll thank you post again those pictures... my email is neko.katse@gmail.com if you can send it to me...
Thank and Greetings!
Does anyone know if a double biquad element shown on http://martybugs.net/wireless/biquad/double.cgi would work better with a dish rather than the single one shown here?
dose it have to be a direct tv dish or can it be any dish
I have two houses 600 fee apart I need to connected. This is very cool.
I would like to ask if i used 50 ohm coax to a standard satellite meter can i detect this Wi-Fi signal thru a standard Satellite test meter for installations??? I have to buy the parts to experiment but we just made a can antenna with a direct tv multisat dish and obviously where i live we have tall a$$ trees. but a signal meter would help if this is possible. Not sure though. I figure the voltage would be to low. but im curious is there is somewhere that makes some sort of meter to if this doesnt work.
thanks
chris537
Stupid Question: I have a LinkSys WRT54G router. How do I set it to pickup Wi-Fi signals from other routers? And is it true that you can use two different antena types? I read somewhere that both antenas had to be the same, or you had to turn the other one off. -Don!