cantenna experiments
in [Wireless Internet]
|
From: Jeff Liebermann on 5 Oct 2005 18:05 On Wed, 05 Oct 2005 16:26:32 -0400, bjs555 <aaa(a)bbb.com> wrote: >Ok, I put up pictures at: >http://www.patmedia.net/bseiler/CantennaPics/ The exposed center conductor of the coax cable is *FAR* too long. Doing a coax to board transition is not easy, especially with the fat coax you're using. Continue the bare copper wire shield wrap right up to the end of the coax. Trim the center conductor to where it just barely sticks out beyond the shield. Shave some of the insulation to get the center conductor closer to the SMA center pin. Solder the copper wrap to the SMA ground pins. Otherwise, do it right and get a pigtail or adapter. The probe length should be 1/4 wave (31mm) from the shield on the F connector. You might wanna try a conical probe for improved bandwidth. -- Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 831.336.2558 voice http://www.LearnByDestroying.com AE6KS http://802.11junk.com Skype: JeffLiebermann jeffl(a)comix.santa-cruz.ca.us jeffl(a)cruzio.com
From: dold on 5 Oct 2005 18:19 bjs555 <aaa(a)bbb.com> wrote: > Wow, was I wrong! Now I see a 30 dB difference in Netstumbler when I > aim the cantenna for minimum and maximum signal. I get about 10 dB > better than the maximum signal with the original rubber duck antenna. That sounds about right. > it to the client card. It must have broken off due to moving the cable ;-) opps.jpg (I assume "oops") shows a lifted center conductor, but I don't see the shield attachment point. It should be coax as much as possible, with the shield and center conductor separated as little as possible, soldered to appropriate contact points. -- --- Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
From: dold on 5 Oct 2005 18:24 bjs555 <aaa(a)bbb.com> wrote: > I've done some more testing. I don't see any difference by using one > can instead of two. That is, shortening the length to 6 inches. Easier > to aim. Maybe there are differences on the order of a couple of dB > that I don't see in my ramshackle setup. That seems to be true for the USB dongle in a can as well. Two cans gives marginally better gain, but it is also much more directional. I thought that was good, but in use, the friend that I gave it to found it too hard to keep pointed at the WAP (using a photo tripod), and preferred a single larger diameter can. http://www.rahul.net/dold/clarence/usb-can/im000742-800x600.jpg -- --- Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
From: dold on 5 Oct 2005 18:29 dold(a)xrexxcante.usenet.us.com wrote: > bjs555 <aaa(a)bbb.com> wrote: >> Ok, I put up pictures at: >> http://www.patmedia.net/bseiler/CantennaPics/ > Rearrange the F connector in the can so that the shielded portion is barely > exposed, just enough for the attaching nut. The exposed inner conductor of > the probe should be 1.21". It looks like the total lenght of your F-Connector and probe is 1.21 inches, so the exposed conductor is substantailly too short. -- --- Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
From: bjs555 on 5 Oct 2005 18:58
>opps.jpg (I assume "oops") shows a lifted center conductor, but I don't see >the shield attachment point. > >It should be coax as much as possible, with the shield and center conductor >separated as little as possible, soldered to appropriate contact points. The wire you see twisted around the shield extends out behind the cable and is soldered to two ground contacts. The shield must be aluminum or something - I couldn't solder to it so I twisted some bare wire around it tightly. That's probably bad for long term use as the connection could oxidize but ok for a quick test. And thanks to you and Jeff I now know that I should make the exposed center conductor as short as possible. I'll try that tomorrow. Bruce |