Antenna Kaleng COBA 1

8/13/2019 Antenna Kaleng COBA 1

1/31

Antenna Testing

This web page shows a number of home made and purchased antenna that I havetested. The equipment for doing this testing is described inExtending Wifi Range

using an Antenna The software used is Netstumbler. There were two different accesspoints used. The access points for the can antenna was 2 miles away and the accesspoint for the dishes was 5.6 miles away. The two different access points were neededbecause the dishes have a lot greater gain than the cans.

The first one is just two can antenna in a shotgun setup. The connectors for this setupwould probably cost more than it is worth but it does improve performance. It mightadd as much as 3db.
http://windsurf.mediaforte.com/roadtrek/wifi/wifi.htmlhttp://windsurf.mediaforte.com/roadtrek/wifi/wifi.htmlhttp://windsurf.mediaforte.com/roadtrek/wifi/wifi.htmlhttp://windsurf.mediaforte.com/roadtrek/wifi/wifi.htmlhttp://windsurf.mediaforte.com/roadtrek/wifi/wifi.htmlhttp://windsurf.mediaforte.com/roadtrek/wifi/wifi.html


2/31


3/31

If two are good then three must be better. I do not think you get 3db for every oneyou add but it does improve a little. Since db is a log scale, 3 db increase would bedouble the power level.

I actually kept increasing this to 5 cans just to see what would happen. Three seemedto be the best and after that it started to drop off. An open stub made things muchworse so all inputs need to be connected. The source was a Netgear home style routerconnected to an antenna about 2 miles away. Here is what that looks like.


4/31

The hardware connecting these cans is not optimum. BNC connectors are really onlygood to about 500 MHZ. Using a splitter rather than a Y would also make a bigimprovement. This is what I had to play with and it worked but could be improved on.

Some people feel that long cans work better. I did see a little increase but not nearlyas much as the shotgun cans above. This is made out of dryer duct.


5/31

Here is another variation, which does use a can that is of the optimum size. It is 4inches in diameter and over 6 inches long.


6/31

Now lets take a look at the same can with a funnel on the end.


7/31

Here are the Netstumbler plots for these two options.


8/31

The funnel adds about 2 db.

The following is another 4 inch diameter can but it is shorter.


9/31

Here is a 3.5 inch diameter can. Now lets compare them to the can above with thefunnel.


10/31

Here is the Netstumbler plot for these 3 cans.


11/31

The can with the funnel is very similar to the much smaller 4 inch can. The 3.5 inchcan

Did not do so well.

Some people like parabolic dishes and USB radios. I tried several versions and didnot find one that worked as well as the cans shown above.


12/31

I decided to try and put one in a can. It worked but not very well. Part of the problemis that you need to know exactly where the antenna is inside the plastic case. It thenneeds to be mounted at the correct point inside the can. The standard can antenna wasmuch easier to build and get a good one the first time.


13/31


14/31

Here is a view of a test bench that I setup to compare the different antenna I havebuilt. I use a distant AP and switch between antenna using Netstumbler to do thecomparison.

Now for a real antenna. If you had two of these and they faced each other, you couldprobably do 8 to 10 miles. It has a gain of about 18 to 20 db.


15/31

The warning label states that no one should get close than 12 feet.

Notice that this dish uses a can antenna for the driver. This is not optimum as it onlydrives about 20 inches of a 36 inch diameter dish. This assumes a 4 inch diameter canthat is 6 inches long. Here is a diagram that shows how the edges of the can block theoutside edge of the dish.


16/31

Here is another dish that uses a biquad driver. This dish is what is called an off centertype which means the feed horn is not in line with the signal. This makes it muchharder to point. This dish came with a double feed horn for connecting to twosatellites. That makes it less sensitive to vertical position because the dish is muchtaller than it is wide. I had hoped this would do much better than the dish above but itwas really about the same. The biquad driver could be improved by adding 4 pieces ofcircuit board around the edges.


17/31


18/31

High gain grid antenna can be purchased for less than $50 and probably work betterthan these dish antenna but you sure learn a lot more by building your own. Here is apicture of a 24DB Pacific Wireless grid antenna. It has about 5 or 6 db better signal

levels than the dishs shown above.


19/31

One of the problems related to setting up any outside antenna is cable length. Thereare two ways around the problem. The first way is to mount the receiver in a weather


20/31

proof box near the dish. The advantage is the short cable needed from the antenna tothe receiver. You loose very little signal. One of the problems with this solution isthe need for power at the dish for the receiver. If you choose to use something like aWRT54GL (running custom software) as your receiver, you can then do power overEthernet which uses some of the extra lines in cat5 cable to provide power to the

router. Be careful as there are two standard for power over Ethernet and they putpower on opposite lines in the cable. In case you are interested in the custom software,check out http://www.linksysinfo.org. Look in the forums section under WRT54G andDD-WRT. Lets look at a picture:


21/31

The second solution for the cable problem is to add an amplifier. You can then runvery long lines without a problem. A DC injector is used to put power on the cable.


22/31

Normally a 9 volt power supply would be connected to the DC Injector. Here is apicture of a 1 watt amplifier which is the largest that can be used outside the military.

The issue with this solution is cost. The amp and injector cost about $260. Thesecond issue is that some antenna seem to have a lot of noise when amplified this

much.

As a test, I borrowed 4 commercial antenna and tested them with and with out theamplifier. The results are interesting. Lets start with the smallest one and go to thelargest one. Here is a picture of a 9dbi HG2409Y made by HyperLink Technologies.


23/31

Here is a plot from Netstumbler first with out and then with the amplifier. The sourceis a commercial WISP that is 5.6 miles away. They are using a AirPointPro

transmitter which includes its own antenna.


24/31

This antenna appears to have lots of noise and that causes the amplifier to not helpmuch. It also seems to miss a lot of data. I have no idea what the term for this wouldbe but I have heard it called picket fencing.

Now lets look at the same data for a 12dbi antenna made by the same company. It is

model HG2412Y. First a picture:


25/31

Now for some NetStumbler data.


26/31

Again adding the amplifier may have reduced the noise some but it did not do exactlywhat we wanted.

Now lets look at the Casigrain dish. First a picture:


27/31

Now lets look at the NetStumbler data. The lower portion has no amplifier and the


28/31

higher portion includes the amplifier. The noise increased a lot but so did thesignal. This is more like what I would have expected.

So a small dish was good, lets look at a big dish. This is a commercial 25dbi dish.


29/31

Here is the NetStumbler data. Again this looks more like what I would expect. Thenoise and the signal both get amplified.


30/31

Now just for comparison, I will include the NetStumbler data from the dish 500 withthe home made biquad driver which was pictured above.


31/31

It looks as good or better than the commercial dish. There is more usable siganl afterthe amplification.

This web page is a work in process. I hope it gives people ideas about what is

possible.

Antenna Kaleng COBA 1

Documents

Transcript of Antenna Kaleng COBA 1