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3453 posts

Uber Geek


  #781912 14-Mar-2013 20:28
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Also using a smaller antenna can sometimes help as the router will pick up less 'noise' from other devices such as wireless security cameras (big problem) cordless phones and other such devices. However this only works if your laptop is within one or two rooms away from the router. If your router has a transmit power setting, set it to maximum or high to increase your signal to noise ratio when using a smaller antenna.

Another thing to note is that when you were getting -45, its wayyyyy to strong.

Your ideal signal is between -55 and -70. Once you go over -50 you will damage the radios inside the router and your laptop over time. Much like people, if they shout at each other, they will go deaf. I especially laugh at mac users who use the built in wireless of their desktop mac to connect to a router less than 50cm away.

-45 is higher than -50 which is higher than -70 because they are numbers below 0 which not alot of people realise.

As a side note, has anyone noticed how some new telecom routers come with their transmit power turned down slightly (configurable in the web options)
I think this is to lower urban noise in the 2.4ghz band and increase performance.

Ray Taylor
Taylor Broadband (rural hawkes bay)

There is no place like localhost
For my general guide to extending your wireless network Click Here

7615 posts

Uber Geek


  #782051 15-Mar-2013 07:59
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Hi Ray, to permanently damage an RF receive chain in an WiFi radio with -45dBm would not be possible, I would expect them to deal with significantly more than that (0dBm or more) and recover immediately, obviously their performance with high levels will suffer while that signal exists. From testing I have done most receivers will maintain usable linearity up to around -30dBm and suffer little performance drop.

Most enterprise APs are designed to maintain this type of linearity, and I know Aerohive for example assume -35dBm as a normal maximum signal.

The UBNT Airmax kit does not like more than -50dBm before it starts to loose linearity and the error rate rises, then again it typically has a lot more bottom end sensitivity than a typical indoor AP as its more directed at WISP work that demands longer haul service, hence setup differently.



23395 posts

Uber Geek


  #782472 15-Mar-2013 20:14
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Im am wondering if my habit of putting my S2 ontop of the AP on the bedside table was somewhat contributing to the death of its 5GHz radio.

It would go to -100dB since I dont think the android wifi drivers are set up to handle positive dB readings. Have since moved to charging the phones on the other side of the bed so no more issue with it, about -25dB is all they get up to there.

And measuring noise with things like inssider is pointless since it doesnt give you noise readings, so you wont see any "hidden" ssid's, any peoples leaking microwave ovens, wireless cameras, xbee type radios, wireless keyboards or other 2.4GHz crap.

Noisefloor according to my old laptops card connected to the big antenna on the roof was about -75dB when I last checked, it also seemed that netstumbler had a limit of about 300 networks it would show active at any given time. 2.4GHz is useless in urban areas.


7615 posts

Uber Geek


  #782476 15-Mar-2013 20:20
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Hi, as said, permanent damage, unlikely, immediate deafness in the presence of nearby loud in band signals, yes.

You must temper this with the fact that modern wideband digital wireless kit is very much devoid of real filter components, not like the old days when we built receivers (something I did as a profession) with real honest cavity filters and lumped component filters that protected the active devices from high levels of off channel energy.

That said, its pretty hard to understand how a RF front end subjected to signals upto 0dBm can suffer permanent damage, immediate non performance, yes, long term deafness, very unlikely.


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