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I'd like to know technically how to diagnose whats causing poor signals and how to improve: Now I have a D-Link DIR-655 and its signal level is set to full, but the router model should not be the primary thing. I also have a custom antenna, specifically:

Here are my SNR calculated with KISMAC at different distances:

-1 Feet: 47

-20 Feet: 15

Now at 15 it seems signal is low, the connection bad, so I'd like to know:

  1. What is a good SNR, IE: what should be your SNR to get a great connection.

  2. How to diagnose if anything is causing a bad SNR.

  3. How to improve it, wifi router settings, antennas.

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Signal to Noise ratio is just one aspect. You might have great SNR but if too many devices are trying to occupy the channel at the same time you get poor throughput. A good SNR is one that allows you to max out your router connection speed - and that varies by model of course.

Bad SNR is usually caused by interference - both in the sense of objects in the signal path and other transmitters. Placement and orientation of the antenna(s) can be critical and it's often trial and error that determines what's best. Wifi router power and channel settings are usually set at the factory to a "good enough" value and shouldn't be messed with unless you've got a really good reason to do so. And of course the SNR is dependent on the system you're using to get to the router. A bad antenna (or other problem) on the laptop / desktop can drop the SNR too.

Sometimes it's just a matter of expectations. Router manufacturers tend to overstate the throughput of their devices. They spec them at "IDEAL" conditions and of course your house or office isn't going to be IDEAL. You may need to adjust your expectations - which is usually a matter of asking others with similar hardware what they are experiencing. I have a wifi system with a 54 Mbit spec'd rating, but I'm satisfied with a real world value of about half of that in a three story house with thick walls.

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SNR, or Signal to Noise Ratio, also dBm, or decibel margins, is a measurement of how strong a signal is through noise of the medium it is traveling through. Lots of things can cause noise for a wireless network.
Noise is most often caused by other devices transmitting in the same range, microwaves, nearby power lines even, but there are countless things that can interfere.
As far as improvement goes, antennas or repeaters to boost signal strength will be the best option, providing more coverage (more access points to allow signals to be generated closer to where your computer will be) is also a good option.
This page goes over SNR values for wireless networks pretty well.

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What other nearby networks does KISMAC report? Any using the same channel as you? Perhaps you could try running on a different channel.

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