Fluctuating WiFi signal

Anyone know what could be causing my WiFi signal to fluctuate so much?

In the room where the router (O2 box II / Thomson TG585v7) sits, the signal is full. In the living room, 25ft and two plasterboard walls away, it goes from "one bar" to "four bars" while the laptop is stationary (see inSSIDer graph below for a more precise view).

It goes up and down so fast that the laptop's signal meter can't keep track, but with inSSIDer you can see just how frequently it fluctuates.

This is the case on channel 13; it was the same on channel 1 and when I let the O2 box select channel automatically. I haven't tried channels in between but there are a fair few other networks there.

It was not the case with my previous (2700HGV) router, which was positioned in the exact same place.

In the graph below, the pinkish line is my signal, all others are neighbours.

Screen shot at Imageshack

Edited by beneix (Mon 08-Mar-10 08:47:38)

My guess is that one of your neighbours is on the same channel as you and their signal is interfering with yours in the sitting room, but is too weak at the router to have any effect there. Try switching channels and see if that helps.

In reply to a post by brightd:

My guess is that one of your neighbours is on the same channel as you

Nope, I have followed the advice and put myself 2 channels away from the closest hotspot. To be clear, there is no other signal (detected by inSSIDer) on my channel or that adjacent to mine.

2 channels is not enough to avoid interference...the channels overlap - so if (for example) you're on channel 6 you'll be getting interference from channels 4, 5, 6, 7 and 8.

Try to separate by 5 channels if possible.

Aha! Thanks JonRennie, will look tonight to see if that is possible. I don't know which of my neighbours have an automatic channel selection and which have selected it manually; many seemed to be on 1, 6 or 11 this morning (not surprisingly).

Can I assume that there will be less interference from the weaker signals in the graph, i.e. if all of the nearby hotspots in the spectrum 4-8 are very weak, I should be able to use channel 6 OK?

Is there an authoratitive site where one can read up on this stuff?

Edited by beneix (Mon 08-Mar-10 08:49:25)

Not that I am aware of

WiFi is one of the dark arts

hi,

the graph is showing a reduction in absolute signal, not signal to noise ratio so it is not interference...

I would say you may have an issue with your AP, unless if course it and/or your laptop are implementing a power saving protocol and backing off the output power when the connection is idle..

Also many laptop wifi receivers switch off the LNA (that is the receive amplifier) to conserve power when idle too. this can show a ~20dB drop in signal.

Apple MACs adjust power, the signal strength from them to an AP tends to be fairly constant over a range of distances as the MAC looks at the quality of the link and reduces output power to suit.. Its a sensible and clever power management method but can confuse people.

cheers

In reply to a post by JonRennie:

2 channels is not enough to avoid interference...the channels overlap - so if (for example) you're on channel 6 you'll be getting interference from channels 4, 5, 6, 7 and 8.

Try to separate by 5 channels if possible.

Oh dear, not this old chestnut again - wi-fi is designed so that several devices can co-exist on the same channel - it's because they don't all transmit at the same time. How do you think large hotels cope with lots of people sharing the same wi-fi channel ?

Wi-fi signals have quite a short wavelength, and they can be reflected by metal objects in the vicinity - including those carried in people's pockets. When two (or more) signals arrive in the same spot out of phase (because at least one has been reflected there), then they can have a cancelling effect and the effective signal strength is reduced. Radio signals are no respecters of walls or boundaries, so it's even possible that reflections could be coming from neighbours in terraced or semi-detached houses.

Obviously devices can co-exist but if one is trying to avoid interference then being on a quiet channel can only make things better.

Given the more detailed analysis by Kijoma I think we're both barking up the wrong tree, but thanks for the condescending tone anyway.

I also own a Thomson TG585v7, and it's WiFi performance is quite possibly the worst I've ever experienced. Fortunately I don't have to use the wireless too often, but would be interested if you find a reason or solution