2mw xmit power better than 33mw - weird results

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jensjakob
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Joined: 07 Jul 2006
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PostPosted: Mon Jul 10, 2006 8:52    Post subject: 2mw xmit power better than 33mw - weird results Reply with quote
Hi,

Just tried to set my xmit power to 2mw - normally I run about 33mw.

The very weird thing,is that I get a better signal to noise ratio at 2 mw than at 33mw.

Very weird but interesting.

Distance from 54GS to AP is about 12 meters, and there is a couple of walls between.

/JJ
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DrJunge
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Joined: 10 Jun 2006
Posts: 32

PostPosted: Mon Jul 10, 2006 20:23    Post subject: Re: 2mw xmit power better than 33mw - weird results Reply with quote
jensjakob wrote:
The very weird thing,is that I get a better signal to noise ratio at 2 mw than at 33mw.
Distance from 54GS to AP is about 12 meters, and there is a couple of walls between.
I bet the walls either have steel reinforcements (most likely) or some major electricity/gas or heating mains run right through the max. E-field of your antennas. We had a similar situation when installing data transmission in the container terminal of Hamburg Harbour: The link quality was so appaling that we increased the power to get an even worse S/N-ratio. Extrapolating our data lead us to reduce the transmission power in order to get a higher S/N-ratio.
The trick is to use line of sight communications. If you have got multiple reflections reduce you output power as much as possible.
dcd
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Joined: 08 Jun 2006
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PostPosted: Mon Jul 10, 2006 22:33    Post subject: Reply with quote
I can confirm this with almost identical setup, except its 1 ceiling in the way, not 2 walls

just tested, my snr @ 2mw is about 5db higher than when tx @ 100mw
jensjakob
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Joined: 07 Jul 2006
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PostPosted: Mon Jul 10, 2006 22:42    Post subject: Good info - should be in the Wiki Reply with quote
Who can put this into the Wiki.

It is an even better argument than being able to boost the signal - being able to lower the signal and achieve better performance (and longer life of the router) !
dcd
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Joined: 08 Jun 2006
Posts: 90

PostPosted: Mon Jul 10, 2006 22:58    Post subject: Reply with quote
im using v24 alpha and have strange wireless results, im not convinced its not a bug here

BS mentioned that he has to try other tricks to get xmit power setting to work in v24
jensjakob
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PostPosted: Mon Jul 10, 2006 23:03    Post subject: DD-WRT v23 SP1 Final (05/16/06) std Reply with quote
running here.
0ldman
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PostPosted: Tue Jul 11, 2006 4:20    Post subject: Reply with quote
In my testing, with one sheetrock wall between the AP and my laptop, raising power over 100mw actually lowers connection speed.

At 28mw, I get 54-48mb, at 50mw its steady 54mb. At 251mw, its 24-36mb, without moving the laptop.

Outdoors, raising the transmit power doesn't cause the same problems, and 50mw vs 200mw doesn't hurt the connection at all once you hit about 18mb, about -85dB, it improves it.

Use as low a power setting as gives you stable signal, it has been proven numerous times that raising the transmit power also raises the noise level. These are not super quality transmitters, they're not designed for this, and we're running them out of spec.

Same thing as overrevving a car or overclocking a CPU. Some handle it quite well, others don't, and there are tradeoffs with everything.

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BrainSlayer
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Joined: 06 Jun 2006
Posts: 6978
Location: Dresden, Germany

PostPosted: Tue Jul 11, 2006 4:34    Post subject: Reply with quote
yes and no. a higher power level can increase the stability. but not at too close distances since you have effects like reflections and distortions. my comparisation to this behaviour is always screaming in the ear of someone other. sure the signal is powerfull, but you could not really listen. additionally both sides must hear each other in a good quality or better the same. not just one. if you have a long distance connection, you can test power level adjustments much better
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colindean
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Joined: 08 Jun 2006
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Location: Pittsburgh, PA

PostPosted: Tue Jul 11, 2006 12:52    Post subject: Reply with quote
Using WHR-HP-G54:

SNRs @
2 mW: 49
10 mW: 48
100 mW: 44-45

Noise was always at -98 dB.

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