[TriLUG] solved: can't connect to wap when move it to alternate location
jim at neuse.net
Fri Apr 23 21:28:44 EDT 2010
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From: trilug-bounces at trilug.org [mailto:trilug-bounces at trilug.org] On
Behalf Of Joseph Mack NA3T
Sent: Friday, April 23, 2010 9:22 PM
To: Triangle Linux Users Group General Discussion
Subject: Re: [TriLUG] solved: can't connect to wap when move it to
On Tue, 13 Apr 2010, Joseph Mack NA3T wrote:
> On Mon, 12 Apr 2010, Neil L. Little wrote:
>> Crap, they went out of business! Ok there was a place
>> over on Yonkers road in Raleigh but I see now they went
>> out of business last year.
> I did find a place that would rent a spectrum analyzer.
> Only $1901/mo. At that price, I should buy one.
Story so far ...
Linksys wap works fine at home, take it to the friend's
store, I can't connect to, or find the wap with netstumbler
or iwconfig. Take the wap home it works fine again. Same
thing with two other Linksys waps and another laptop
(admittedly the same type of wifi card). There are two other
waps in the vicinity I can pick up, which I assume are
operating fine. Since my laptop can pick up other waps and
not my waps, I assume the problem is with my wap(s) and not
my laptop(s). If I disconnect the antennas to the wap, I can
connect fine till I'm about 10' away. If I put paperclips in
the antenna jacks, I can connect till I'm about 20' away. If
I put the antennas back on, I can't connect at all.
The store had a 5.8GHz phone system, which I eliminated as
the cause, by turning it off. My 900MHz phones at home had
no effect on the wap. Pete Soper told me that some 5.8GHz
phones use 2.45GHz for one of the directions, which would be
The waps were non-operational during the week, but when I
returned to the store in the weekend, when I could safely
mess with the network, the wap worked fine. Presumably the
interference isn't constant.
hypothesis: wap is going CDMA deaf. Is the interferring
signal in-band or out-of-band? A spectrum analyser ($$$$)
would be just the thing here. Was there a bank of microwave
ovens on the other side of the wall?
John Mitchell kindly lent me his wi-spy v1, an in-band
2.45GHz band scanner. I expected it would take a little
while to figure this thing out, but it was very easy to use.
I could identify waps easily. It didn't take long to find
that 4 different microwave ovens were radiating from ch7-11.
I was surprised that they were all on the same freq and
relatively narrow - I thought they were 100's of MHz wide.
Looking with google, I find they're quite tightly regulated
freq wise. The microwave ovens weren't detectable more than
For John's device there is a Linux driver, by the kismet
people, which I got going in short time, and which gives a
nicer display than the windows wi-spy display. John's device
used to be about $99, but isn't made anymore. It's been
replaced by a $199 device with similar specs and there is a
new $99 device which spec-wise is about half of John's v1
device. I could have gone for the device I had at $99, but
not the replacement at $199.
After a null trip to the store in the weekend when I found
the wap working fine, I returned during the week when the
wap wasn't working. Then the wi-spy to show no inband
interferrence. All I saw was the waps I could already see
Thus there was no in-band interference. It had to be out of
band interferrence. I did the following
o put a 4db (and 8db) attenuator in the antenna line - the
wap started working. Presumably the 3rd order intercept
point had been dropped enough for the device to start
o put a 4 pole 60MHz bandpass filter centered on ch 6 in the
antenna line - the wap started working.
The interference was almost certainly out-of-band.
I didn't know the brand of the other waps in the vicinity
which appeared to be working just fine. They weren't
bothered by the putative out-of-band signal and I assumed
they were getting the same amount of signal as were my waps.
Presumably I could have walked around and found out what
they were. I assumed they had a different RF frontend than
the Linksys. Looking in the digi-key catalog, I find ceramic
filters for wifi front ends at $0.80 each. Presumably the
LinkSys box doesn't have a filter, and I wasn't up for
surgery on it. Presumably I needed any other front end. I
assumed all wap manufacturers had their own front ends,
presumably many with filters. I bought a TP-Link wap from
Intrex and it worked first time.
Thanks to John for his wi-spy.
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!
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