Directional double BiQuad WiFi antenna 2.4GHz by ChatToBrian is licensed under the Creative Commons - Attribution - Non-Commercial. Then this directional BiQuad WiFi antenna might come handy. With this antenna you can increase the working distance of your WiFi by up to many hundreds of meters. WiFi Antenna 5.8Ghz Omni BiQuad MACH 4B Antenna for FPV SUPER LONG RANGE BOOSTER RP-SMA. By Custom Cables Group LLC. $19.99 $ 19 99. Ochoos Original High Gain 5.8GHz 12dB Double Biquad Long Range Directional FPV Antenna SMA - (Mode: Soft Antenna) by Ochoos. $52.99 $ 52 99. FREE Shipping on eligible orders.
Lo and behold, the humble yet mighty biquad.
The gain figure on one of these things is pretty impressive, you're looking at 8-10 dBi. The double biquad detailed a bit lower is about 2-3 dBi higher. A quad biquad (an octquad?) would be around 1 dBi higher still.
Construction
Construction is very simple. I used a bolt, sanded so as to be solderable on a beer can taped to a cardboard backing, as seen here:
The wire is enameled copper transformer wire; For a double or a quad, this is necessary, but any old wire can be used for a single biquad.
The red sheet is electricians' insulating tape, used to ensure insulation between the feed points.
Dimensions are pretty exact: Tolerance is about 5% and bandwidth about 10%, though it's ~25% to unity gain. Each square edge is an exact quarter wave of the centre frequency you're interested in. This is about 31mm for the 2.4GHz 802.11b/g band. The coax feed connects, in these images, above and below. A common mistake is to connect side by side, resulting in a folded dipole which has piss-poor performance.
The reflector, ideally, is infinite in size. In the real world, however, the radiation pattern does not extend more than about a quarter wave around the antenna's sides. Build too big rather than too small for the reflector plate. Also ensure a good connection between the plate and coaxial ground/braid.
The distance between the antenna elements and the plate must be as near as damn it lambda/8 (half a quarter wave), this causes constructive interference between the direct and reflected waveforms and adds about 80% to the forward gain of the antenna.
A much simpler and very easily rigged antenna is an unreflected biquad. Build as described above but omit the reflector. I use such an antenna for UHF (675MHz centre) DVB-T transmissions. It compares very favourably to commercial Yagis. Gain is about 6 dBi and it has two lobes, front and rear.
The feed point MUST be perpendicular to the plane of the antenna, otherwise the coax braid will really screw things up.
The double biquad is as the biquad but with another square on the end and the two long edges are a half-wave. At the crossing point, the conductors do not contact (hence enameled wire).
Use
Polarisation is important with any antenna, and biquads are a bit special. They aren't as polar as a dipole but they still have around 50% more gain when oriented with respect to source polarisation. Biquads are polar perpendicular to their long axis so in my photos the polarisation is vertical.
To severely abuse a biquad, mount it at the focal of a satellite dish (for perhaps TV). You can get gain in the 20 dBi range like that, this is easily capable of transmitting 802.11b (b is better at range than g is) over ten miles to a similar antenna and half a mile to a mile to an omni. Between two WRT543GLs with DD-WRT installed and 220 milliwatts output, I was able to traverse around 15 miles at 'excellent' signal quality. Fifteen miles was the limit because I couldn't actually find any two points more than that distance apart with a line of sight. I'd estimate detectability and possibly even data transfer at 200 miles per watt.
Have at it, have fun, and this is in AV because antenna related topics traditionally have been.
The gain figure on one of these things is pretty impressive, you're looking at 8-10 dBi. The double biquad detailed a bit lower is about 2-3 dBi higher. A quad biquad (an octquad?) would be around 1 dBi higher still.
Construction
Construction is very simple. I used a bolt, sanded so as to be solderable on a beer can taped to a cardboard backing, as seen here:
The wire is enameled copper transformer wire; For a double or a quad, this is necessary, but any old wire can be used for a single biquad.
The red sheet is electricians' insulating tape, used to ensure insulation between the feed points.
Dimensions are pretty exact: Tolerance is about 5% and bandwidth about 10%, though it's ~25% to unity gain. Each square edge is an exact quarter wave of the centre frequency you're interested in. This is about 31mm for the 2.4GHz 802.11b/g band. The coax feed connects, in these images, above and below. A common mistake is to connect side by side, resulting in a folded dipole which has piss-poor performance.
The reflector, ideally, is infinite in size. In the real world, however, the radiation pattern does not extend more than about a quarter wave around the antenna's sides. Build too big rather than too small for the reflector plate. Also ensure a good connection between the plate and coaxial ground/braid.
The distance between the antenna elements and the plate must be as near as damn it lambda/8 (half a quarter wave), this causes constructive interference between the direct and reflected waveforms and adds about 80% to the forward gain of the antenna.
A much simpler and very easily rigged antenna is an unreflected biquad. Build as described above but omit the reflector. I use such an antenna for UHF (675MHz centre) DVB-T transmissions. It compares very favourably to commercial Yagis. Gain is about 6 dBi and it has two lobes, front and rear.
The feed point MUST be perpendicular to the plane of the antenna, otherwise the coax braid will really screw things up.
The double biquad is as the biquad but with another square on the end and the two long edges are a half-wave. At the crossing point, the conductors do not contact (hence enameled wire).
Use
Polarisation is important with any antenna, and biquads are a bit special. They aren't as polar as a dipole but they still have around 50% more gain when oriented with respect to source polarisation. Biquads are polar perpendicular to their long axis so in my photos the polarisation is vertical.
To severely abuse a biquad, mount it at the focal of a satellite dish (for perhaps TV). You can get gain in the 20 dBi range like that, this is easily capable of transmitting 802.11b (b is better at range than g is) over ten miles to a similar antenna and half a mile to a mile to an omni. Between two WRT543GLs with DD-WRT installed and 220 milliwatts output, I was able to traverse around 15 miles at 'excellent' signal quality. Fifteen miles was the limit because I couldn't actually find any two points more than that distance apart with a line of sight. I'd estimate detectability and possibly even data transfer at 200 miles per watt.
Have at it, have fun, and this is in AV because antenna related topics traditionally have been.
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 fromFreecycle. 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:
![Biquad Biquad](https://i.ebayimg.com/images/g/1G0AAOSw-nZTmxuh/s-l300.jpg)
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.
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 anomnidirectional mini whip antennawith 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.
![Wifi Wifi](http://www.brest-wireless.net/albums/AntenneQuads/dsc01296.sized.jpg)
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 byTranzeo.