Wireless
enthusiasts have been repurposing satellite dishes for a couple years now. This summer the longest
link ever was established
over 125 miles
http://pasadena.net/shootout05/
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 do not have to scrounge around for the
perfectly-sized soup can.
http://www.turnpoint.net/wireless/cantennahowto.html
We did have to buy some specialized parts before getting started though.
over 125 miles
http://pasadena.net/shootout05/
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 do not have to scrounge around for the
perfectly-sized soup can.
http://www.turnpoint.net/wireless/cantennahowto.html
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.
http://www.smelectronics.us/typenconnectorspanel.htm 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
http://www.wlanparts.com/product/RPTNCNM24 that we'll use to connect our antenna to a Linksys WRT54G access point. The short pigtail is a
RP-MMCX to
http://www.wlanparts.com/product/RP-MMCXNM12
N-Male pigtail so we can connect to our
Senao 2511CD PLUS EXT2
http://www.wlanparts.com/product/NL2511CDPLUSEXT2
WiFi card which is pictured. We also purchased 10 feet of
WBC 400 coax cable
http://www.hyperlinktech.com/web/cable_feed400.php
so we wouldn't have to sit with the dish in our lap. We got our surplus DirecTV dish from
Freecycle.
http://freecycle.org/
We'll cover the reason for the mini butane torch later.
Trevor Marshall built one of the
first biquad WiFi antennas
http://www.trevormarshall.com/biquad.htm
found on the internet. We followed the slightly more thorough instructions
found at martybugs.net.
http://martybugs.net/wireless/biquad/
Here are the raw materials we started with:
The first step in building the element was stripping and cutting a 244mm length of wire.
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.
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.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.
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.
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
No comments:
Post a Comment