what type of adapter to use?

I got a SpeedTouch 570 router and I'm using the SMC USB adapter (the little thumbsized one) to recieve, with extremely poor performance.

Would it make much of a difference if I get the larger type receivers? (E.g Linksys, not powered by USB)

Reply to
alphatango
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It's not the USB (versus ethernet) that's causing the problem. It's the tiny antenna that's in the thumb size USB devices.

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gold PCB is the antenna. Some USB devices have even smaller antennas.

First, some basics. A 3dB increase in antenna gain will increase your range by 1.4 times. 6dB will double the antenna range. 12dB will increase the range by a factor of 4.

Opinions seem to vary as to the gain of the tiny chip antennas. My guess is about -3dB gain. The USB radios with the flip up antennas have about 1dB gain. The typical wireless access point, running as a client adapter, has a rubber ducky antenna. The gain roughly varies with the length of the omnidirectional antenna. 4.5" 2dBi 6.0" 3dBi 11.0" 6dBi

So, if you go from a USB thumb device with -3dB antenna gain, to a larger box with a 6" (stock) antenna with a gain of 3dB, you'll have a

6dB net increase in gain, which will double your range.

The real advantage of a larger box radio is that you can either install a reflector to increase the gain even more:

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you can attach an external high gain antenna from a commercial vendor. That's very difficult to do with a USB radio, which rarely has an antenna connector.

If you go this route, be sure that whatever you buy has a "client mode", where you can use the box as client radio. You might also get away with an internal PCI card or PCMCIA card with an external antenna connect.

Reply to
Jeff Liebermann

what about the router? do they differ in terms of transmission power?

Reply to
alphatango

No, not much. The commodity wireless routers all transmit at about

+15 to +17dBm. There is a new class of router that has a built in power amplifier that transits about +29dBm. They're also kinda expensive at $600/ea. I consider those little better than jammers. Yes, you'll hear such a high power access point at a much furthur distance, but because your client radio is still transmitting about +15dBm, the access point will not hear you at the same range. If you want to increase range, then the transmit power has to be increased at both ends of the link. All the a high power access point does is create more interference for everyone.

The nice thing about improving the antenna (at either end) is that it improves both the transmit and receive signal, thus improving your range in both directions.

Reply to
Jeff Liebermann

One of "those"? Those what? I'll guess that you mean a DLink DWL-122. I added a coax pigtail and external antenna to one of those, but never had time to do any measurements. I would post a photo, but it's on a neighbors roof and not easily accessible.

If you look at the photo at: |

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circuit board PIFA antenna has 3 connections. The one on the left is ground. The one just to the right of this one is where the center connection goes. The connection near the middle goes nowhere and is just for mechanical support.

I would NOT try to solder a relatively large SMA connector in place of the PIFA antenna. The leads will be too long and there's not enough board area for a stable mechanical connection. It will break. A much smaller SMB connector might work.

I unsoldered the antenna, and connected a .141 dia semi-rigid coax pigtail to the left two connections. |

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is VERY important to keep the exposed part of the coax center wire as short as possible. There is additional ground area on the circuit board all around the RF connection and I used it liberally to maximize the ground connection area. The coax came straight up from the board (in the direction of where the PIFA antenna was replaced) in order to minimize the exposed center conductor length. I forgot which side of the board I installed the coax cable.

Reply to
Jeff Liebermann

Jeff,

I have one of these too.. what are my options for replacing the antenna ? Mount an SMA connector ? Which part does the centre coax go to ?

Doz

Reply to
Doz

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It is VERY important to keep the exposed part of the coax center wire

That's the ticket.. Thanks for the info Jeff.

Doz

Reply to
Doz

Is the USB WiFi client in fixed location? You could add a coffee can for a substantial boost in performance.

A friend was using a 6" diameter coffee can, which I found to have lower gain than the 4" diameter two coffee can setup, but the larger can was easier to point at an access point about two blocks away.

Bob Alston's coffee can

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Dold's coffee can
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used the turnpoint calculator to decide where to poke the hole.
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There are also many haphazard designs on the New Zealand page, using USB dongles.
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Reply to
dold

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