[Soekris] interference from two radios - revisited
mitja at muzenic.net
Fri Oct 7 22:37:05 UTC 2005
As I've been told offlist, my mail has been caught in the spam filters. I'll
try to modify it slightly to see if it gets through this time...
I know this topic has been discussed a lot and I've read the archives. I
found Jim Thompson's explanation on http://www.netgate.com/zz_faq.php#67
excellent and I understand the propagation issues behind it. But I still
need a bouncing board for my thoughts, so please bear with me.
I'm working on a project to provide indoor wifi coverage into a building
mostly made by 30cm concrete with rebar.. Think nuclear shelter, only it's
not government or military, but a huge private mansion designed by a mad
architect. The rebar is most probably grounded as well since I've never seen
so much LOS signal loss - the walls seem to suck the signal out of the air.
Put an AP in the middle of the corridor, walk a few meters away and watch
the signal level sink as a stone - that bad.
Jim's explanation on why two AP's in close proximity won't work assumes (as
I understand it) free space around the two AP's and the antenna on or near
the AP itself. In my case, I'll probably have two antennas, one on each wing
of the building, and the signal loss in structure is so big that the signal
from one AP antenna is undetectable (as far as my measuring equipment can
tell) at the other location. I wonder how this changes the situation?
The second problem is that for architectural reasons the AP equipment must
be in close proximity (one telco cabinet) and the two antennas separated by
a longish cable, one into each wing. I'll be having approx. 10m of 0.5dB/m
cable from AP (net4526 running OpenBSD + 5354 Aries MP in 11b mode) to the
antenna (4 dBi omni). My question is: assuming no interference from the
radiating elements - antennas (they should be in decently shielded areas of
the building) - , how much leakage will there be from the soekris boxes in
physical vicinity? How will this affect the working of two AP's? Do I even
gain anything by shielding the two cards in separate soekris boxes or can I
simply use both in the same case, thus saving the cost of one net4526?
The third problem is that I've decided to go with ath(4) based cards in
order to try Reyk Floeter's latest hostapd(8) tools to help with roaming.
Does anyone have success stories or practical examples including hostapd(8)?
I went all over the man pages and it looks like there will be some
tutorials/papers by the author but all those conferences are scheduled for
Thanks for any insight you might give me.
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