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Overcoming wireless networking interference problems

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Anonymous
a b F Wireless
September 24, 2004 3:04:37 AM

Archived from groups: alt.internet.wireless (More info?)

Can anyone point me to information on how to diagnose and overcome
interference problems in WiFi networks, please?

Most of the advice I've seen so far is fairly superficial (different
channel, move access point, waggle aerials etc) and has been
ineffective IME.
Anonymous
a b F Wireless
September 24, 2004 5:01:42 AM

Archived from groups: alt.internet.wireless (More info?)

That is good advice. The only other thing to suggest is what about 2.4GHz
cordless phones or a microwave.

Jeff


"Frank le Spikkin" <zaq@invalid.jp> wrote in message
news:Xns956ECE46117FlSxxx@130.133.1.4...
> Can anyone point me to information on how to diagnose and overcome
> interference problems in WiFi networks, please?
>
> Most of the advice I've seen so far is fairly superficial (different
> channel, move access point, waggle aerials etc) and has been
> ineffective IME.
>
Anonymous
a b F Wireless
September 24, 2004 5:01:43 AM

Archived from groups: alt.internet.wireless (More info?)

"Jeff Durham" <jdurham.outdoor.life@cinci.rr.com> wrote in message
news:WlK4d.106739$787.46588@fe2.columbus.rr.com...
> That is good advice. The only other thing to suggest is what about 2.4GHz
> cordless phones or a microwave.
>
> Jeff
>
>
> "Frank le Spikkin" <zaq@invalid.jp> wrote in message
> news:Xns956ECE46117FlSxxx@130.133.1.4...
>> Can anyone point me to information on how to diagnose and overcome
>> interference problems in WiFi networks, please?
>>
>> Most of the advice I've seen so far is fairly superficial (different
>> channel, move access point, waggle aerials etc) and has been
>> ineffective IME.
>>
>
>
Have you used something like Network Stumbler to look for what networks
already exist in your area? Do this with your AP turned off. There might
be several networks in your area, on different channels, that are
interfering.

When setting up a wireless network for the marina where I keep my boat, I
found at least 5 other APs that broadcasted ocasionally. And one seemed to
knock me off my network any time it popped its ugly head up. goo that it
was rarely present.

You might also advise what is the problem you are trying to solve? You say
"interference" but is the real issue that you cannot communicate with your
AP? The root cause might be a range or obstacle issue.

--
Bob Alston

bobalston9 AT aol DOT com


---
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Anonymous
a b F Wireless
September 24, 2004 11:27:31 AM

Archived from groups: alt.internet.wireless (More info?)

"Bob Alston" <bobalston9NOSPAM@aol.com> wrote in
news:RsK4d.289234$Lj.95971@fed1read03:

>
> "Jeff Durham" <jdurham.outdoor.life@cinci.rr.com> wrote in
> message news:WlK4d.106739$787.46588@fe2.columbus.rr.com...
>> That is good advice. The only other thing to suggest is what
>> about 2.4GHz cordless phones or a microwave.
>>
>> Jeff
>>
>>
>> "Frank le Spikkin" <zaq@invalid.jp> wrote in message
>> news:Xns956ECE46117FlSxxx@130.133.1.4...
>>> Can anyone point me to information on how to diagnose and
>>> overcome interference problems in WiFi networks, please?
>>>
>>> Most of the advice I've seen so far is fairly superficial
>>> (different channel, move access point, waggle aerials etc) and
>>> has been ineffective IME.
>>>
>>
>>
> Have you used something like Network Stumbler to look for what
> networks already exist in your area? Do this with your AP
> turned off. There might be several networks in your area, on
> different channels, that are interfering.
>
> When setting up a wireless network for the marina where I keep
> my boat, I found at least 5 other APs that broadcasted
> ocasionally. And one seemed to knock me off my network any time
> it popped its ugly head up. goo that it was rarely present.
>
> You might also advise what is the problem you are trying to
> solve? You say "interference" but is the real issue that you
> cannot communicate with your AP? The root cause might be a
> range or obstacle issue.
>
Thanks for the replies Jeff and Bob.

The particular case I experienced this week:
- AP (Netgear DG834G wireless ADSL router) and adapter work fine in
my workshop, rock solid signal, no dropouts in continuous ping
testing and Netstumbler graph.
- At the target premises (small shop in crowded village High
Street), initially appeared to work, some dropouts but acceptable
performance. Strong signal shown on Netstumbler, low noise,
until...
- blattttt, connection lost no signal visible with Netstumbler.
Intermittent reconnection, totally unacceptable performance.
- Netstumbler shows no signal, no access point at all.
- Tried all the tricks, 11b only, 11g only, different channels,
moved the router etc to no avail.
- Interference disappears periodically, but only for a few minutes
at a time.
- Same results on two visits to the site. After several hours of
trying, reverted to a wired configuration.

So the interferer is unidentifiable using the tools to hand, and
I'm helpless to do anything about it - hence my OP question.
Anonymous
a b F Wireless
September 24, 2004 1:39:19 PM

Archived from groups: alt.internet.wireless (More info?)

On 24 Sep 2004 07:27:31 GMT, Frank le Spikkin <zaq@invalid.jp> wrote:

>The particular case I experienced this week:
>- AP (Netgear DG834G wireless ADSL router) and adapter work fine in
>my workshop, rock solid signal, no dropouts in continuous ping
>testing and Netstumbler graph.

Ping for testing a system isn't really that good. You need to move
large amounts of data for testing. Try one of the numerous online
speed tests and run some streaming media to be sure that everything is
working as expected.

>- At the target premises (small shop in crowded village High
>Street), initially appeared to work, some dropouts but acceptable
>performance. Strong signal shown on Netstumbler, low noise,
>until...

How long is initially? Minutes, hours, days? If it's interference,
duz it go away at night, or on weekends?

>- blattttt, connection lost no signal visible with Netstumbler.
>Intermittent reconnection, totally unacceptable performance.
>- Netstumbler shows no signal, no access point at all.

It might be interference. Judging by the general description it
sounds like you might be near a cafeteria or establishment that runs
microwave ovens almost continuously. We had a local market that
effectively ran their sandwitch shop microwave oven erratically all
day long. When it ran, wireless within about 1000ft radius was
futile. I had to borrow a spectrum analyzer to verify. Eventually, I
convinced them to clean the encrusted food off the door seal and life
returned to normal.

I don't think it's a cordless phone. The non-spread spectrum phones
I've watched tend to occupy the bottom channels. They start at the
low frequency edge and dribble up in frequency until they find a clear
channel. The spread spectrum ones are really evil. They use
frequency hopping (FHSS) instead of direct sequence (DSSS). FHSS is
required to hop over the entire band (75 out of 79 channels) before
re-using a channel. It clobbers everything. However, they are also
very low power and are used intermittantly (unless you have
teenagers). No way would one cause a dropout or disconnect unless the
phone were literally next to the radio or access point.
http://www.wi-fiplanet.com/tutorials/article.php/219124...

Another possibility are the new and disgusting metropolitan lans.
This is where the local municipality installs high power store and
forward repeaters on street lights to build a mesh network. Every
mesh network I've seen eventually ends up spewing continuous packets
in its never ending effort to inefficiently send duplicate packets to
the entire network. The problem with these isn't just the excessive
traffic, it's the tendency to use over powered radios for the intended
purpose. Most are running full power (4 watts EIRP) and are fully
capable of clobbering any local traffic. The better units use
multiple radios and channels for store-n-forward, so channel shifting
may not be effective. See:
http://www.tropos.com

A variation on the theme are high powered central access points with
highly directional and steerable antennas. The FCC considers these to
be "point to point" instead of "point to multipoint" and therefore
allows them to use additional power. If you happen to be badly
located, these can be a major source of interference.
http://www.vivato.net

>- Tried all the tricks, 11b only, 11g only, different channels,
>moved the router etc to no avail.
>- Interference disappears periodically, but only for a few minutes
>at a time.
>- Same results on two visits to the site. After several hours of
>trying, reverted to a wired configuration.
>
>So the interferer is unidentifiable using the tools to hand, and
>I'm helpless to do anything about it - hence my OP question.

Did you run this test with the client radio fairly close (a few feet)
from the access point, or is there some distance (or a wall) between
the two? If you're getting dropouts while next to the access point,
the interference must either be massive, or the radio(s) defective.

Try a different client radio. Try removing the antenna from the
access point temporarily to reduce anything it might pickup from a
nearby source of interference. If the problem goes away, it's most
surely something that's being picked up by the access point receiver,
and therefore is interference. However, if the problem persists,
there's something broke with the radios.

If none of this does any good, try to borrow a spectrum analyzer and a
directional dish or patch antenna. You're at a disadvantage with a
spectrum analyzer as you lose the benifits of SS processing gain.
With the signal spread over 26MHz (DSSS) or 80Mhz (FHSS or channel
bonded DSSS), it's difficult to see unless you're close. The gain of
the antenna will help. I built a receive pre-amplifier in the dish
antenna feed in order to improve sensitivity (and largely eliminate
coax cable losses).

If you can find or afford to borrow a real spectrum analyzer, a
tolerable substitute is a FHSS receiver with appropriate software.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5722...
(Does NOT work with Windoze XP). Sensitivity is tolerable, but it has
the adantage of being portable. If the interference is sufficiently
bad to cause a disconnect, it should be easily visible.

My guess(tm) is:
1. microwave oven or industrial platic molding pre-heater.
2. defective access point or client radio.
3. Metropolitan LAN or mesh network interference.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
September 24, 2004 3:46:09 PM

Archived from groups: alt.internet.wireless (More info?)

As viewed from alt.internet.wireless, Jeff Liebermann wrote:

>We had a local market that effectively ran their sandwitch shop
>microwave oven erratically all day long. When it ran, wireless
>within about 1000ft radius was futile. I had to borrow a spectrum
>analyzer to verify. Eventually, I convinced them to clean the
>encrusted food off the door seal

Yecch. If word of that encrustation had gotten out, their sandwich
business might have dropped off to the point where the now-occasional
interference might not have been a problem any longer... :) 

>and life returned to normal.

Except for the employees who had been operating the microwave.
After getting nuked on a long-term basis, some of their kids might
be born with two heads... :) 

--
Jafo
Anonymous
a b F Wireless
September 24, 2004 4:31:48 PM

Archived from groups: alt.internet.wireless (More info?)

Perhaps this is a hardware problem. Can you take it back to the pristine
location and see if everything works? I did have an access point actually
die on me a few weeks ago. It would work for an hour or two and then just
quit responding. When accessing it through its IP address, I could page
through the configuration pages, but then it would slow down, and then quit
responding. That was done through a wired connection.

Jeff


"Frank le Spikkin" <zaq@invalid.jp> wrote in message
news:Xns956E560C74DD7FlSxxx@130.133.1.4...
> "Bob Alston" <bobalston9NOSPAM@aol.com> wrote in
> news:RsK4d.289234$Lj.95971@fed1read03:
>
>>
>> "Jeff Durham" <jdurham.outdoor.life@cinci.rr.com> wrote in
>> message news:WlK4d.106739$787.46588@fe2.columbus.rr.com...
>>> That is good advice. The only other thing to suggest is what
>>> about 2.4GHz cordless phones or a microwave.
>>>
>>> Jeff
>>>
>>>
>>> "Frank le Spikkin" <zaq@invalid.jp> wrote in message
>>> news:Xns956ECE46117FlSxxx@130.133.1.4...
>>>> Can anyone point me to information on how to diagnose and
>>>> overcome interference problems in WiFi networks, please?
>>>>
>>>> Most of the advice I've seen so far is fairly superficial
>>>> (different channel, move access point, waggle aerials etc) and
>>>> has been ineffective IME.
>>>>
>>>
>>>
>> Have you used something like Network Stumbler to look for what
>> networks already exist in your area? Do this with your AP
>> turned off. There might be several networks in your area, on
>> different channels, that are interfering.
>>
>> When setting up a wireless network for the marina where I keep
>> my boat, I found at least 5 other APs that broadcasted
>> ocasionally. And one seemed to knock me off my network any time
>> it popped its ugly head up. goo that it was rarely present.
>>
>> You might also advise what is the problem you are trying to
>> solve? You say "interference" but is the real issue that you
>> cannot communicate with your AP? The root cause might be a
>> range or obstacle issue.
>>
> Thanks for the replies Jeff and Bob.
>
> The particular case I experienced this week:
> - AP (Netgear DG834G wireless ADSL router) and adapter work fine in
> my workshop, rock solid signal, no dropouts in continuous ping
> testing and Netstumbler graph.
> - At the target premises (small shop in crowded village High
> Street), initially appeared to work, some dropouts but acceptable
> performance. Strong signal shown on Netstumbler, low noise,
> until...
> - blattttt, connection lost no signal visible with Netstumbler.
> Intermittent reconnection, totally unacceptable performance.
> - Netstumbler shows no signal, no access point at all.
> - Tried all the tricks, 11b only, 11g only, different channels,
> moved the router etc to no avail.
> - Interference disappears periodically, but only for a few minutes
> at a time.
> - Same results on two visits to the site. After several hours of
> trying, reverted to a wired configuration.
>
> So the interferer is unidentifiable using the tools to hand, and
> I'm helpless to do anything about it - hence my OP question.
>
Anonymous
a b F Wireless
September 24, 2004 8:03:05 PM

Archived from groups: alt.internet.wireless (More info?)

Jeff Durham <jdurham.outdoor.life@cinci.rr.com> wrote:
> That is good advice. The only other thing to suggest is what about 2.4GHz
> cordless phones or a microwave.

I don't see any interference in NetStumbler with two different microwave
ovens on an Orinoco or DLink DWL-122. I suppose some ovens might leak, but when
they first came out, I was working in radar that used a magnetron at the
same frequency. We didn't "see" microwave ovens.:w

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
a b F Wireless
September 24, 2004 8:03:06 PM

Archived from groups: alt.internet.wireless (More info?)

On Fri, 24 Sep 2004 16:03:05 +0000 (UTC),
dold@XReXXOverc.usenet.us.com wrote:

>Jeff Durham <jdurham.outdoor.life@cinci.rr.com> wrote:
>> That is good advice. The only other thing to suggest is what about 2.4GHz
>> cordless phones or a microwave.

>I don't see any interference in NetStumbler with two different microwave
>ovens on an Orinoco or DLink DWL-122. I suppose some ovens might leak, but when
>they first came out, I was working in radar that used a magnetron at the
>same frequency. We didn't "see" microwave ovens.:w

You didn't look hard enough. Leaky microwave ovens are quite obvious.
Here are some sample photos from the Tektronix catalog:
http://www.tek.com/Measurement/cgi-bin/framed.pl?Docume...

There are also hams that have too much time on their hands:
http://lea.hamradio.si/~s57uuu/mischam/magnetr/

Netstumbler works by "active probing" the access point for it's SSID
with a probe request frame (with a broadcast BSSID and a blank SSID),
that is answered by an access point or ad-hoc client with a probe
response frame. Netstumbler won't "see" anything that does't respond.
Neither will any of the 802.11a/b/g sniffers (Wellenreiter).


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
September 24, 2004 9:21:18 PM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> Ping for testing a system isn't really that good. You need to move
> large amounts of data for testing.

What about a long ping packet?
from unix
ping -c 5 -s 1000 host
from windows-cmd
ping -n 5 -l 1000 host

A better tester might be iperf, if you have access to a windows or unix
machine you can use as the host & client at the other end.
This allows long tests. It seems to get funky after 10 minutes, but a
minute is probably sufficient.
Start a server
iperf -s
from the other machine
iperf -c the_host_ip
runs a 10 second test. Reverse host and client roles, or invoke other
iperf options to test the other way. You might need to open a firewall
port 5100 to reverse the roles and make your wireless the server.
< http://dast.nlanr.net/Projects/Iperf/ >

Streaming audio or video pauses and dropouts are obvious indicators of a
network glitch. Unfortunately, those happen on my wired connections, so
they indicate "trouble" under normal traffic conditions.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
a b F Wireless
September 24, 2004 11:29:18 PM

Archived from groups: alt.internet.wireless (More info?)

"Jeff Durham" <jdurham.outdoor.life@cinci.rr.com> wrote in
news:UsU4d.107762$787.44485@fe2.columbus.rr.com:

> Perhaps this is a hardware problem. Can you take it back to the
> pristine location and see if everything works? I did have an
> access point actually die on me a few weeks ago. It would work
> for an hour or two and then just quit responding. When
> accessing it through its IP address, I could page through the
> configuration pages, but then it would slow down, and then quit
> responding. That was done through a wired connection.
>
> Jeff
>
>
I've done that and there's no evidence of hardware problems in the
router or the two flavours of PC Cards I'v etried.
Anonymous
a b F Wireless
September 24, 2004 11:34:51 PM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in
news:mvj8l0tfvgnk2eh2riv3pmm54al2nv6adu@4ax.com:

> Netstumbler works by "active probing" the access point for it's
> SSID with a probe request frame (with a broadcast BSSID and a
> blank SSID), that is answered by an access point or ad-hoc
> client with a probe response frame. Netstumbler won't "see"
> anything that does't respond. Neither will any of the
> 802.11a/b/g sniffers (Wellenreiter).
>

Thanks for that, it confirms what I suspected - that Netstumbler
isn't the right tool where the interference isn't from other WiFi
LANs.
Anonymous
a b F Wireless
September 24, 2004 11:34:52 PM

Archived from groups: alt.internet.wireless (More info?)

On 24 Sep 2004 19:34:51 GMT, Frank le Spikkin <zaq@invalid.jp> wrote:

>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in
>news:mvj8l0tfvgnk2eh2riv3pmm54al2nv6adu@4ax.com:
>
>> Netstumbler works by "active probing" the access point for it's
>> SSID with a probe request frame (with a broadcast BSSID and a
>> blank SSID), that is answered by an access point or ad-hoc
>> client with a probe response frame. Netstumbler won't "see"
>> anything that does't respond. Neither will any of the
>> 802.11a/b/g sniffers (Wellenreiter).

>Thanks for that, it confirms what I suspected - that Netstumbler
>isn't the right tool where the interference isn't from other WiFi
>LANs.

Yep. One clue I forgot to mention is the relationship between signal
strength and S/N ratio. A sure sign of wireless interference is a
high signal strength combined with a rotten (low) S/N ratio. In this
case, the poor S/N ratio is mostly data errors. Microwave ovens do
largely the same thing. Netstumbler is a great help for extracting
signal strength and S/N ratio from both the access point and wireless
client as both of these are broadcast in managment frames.

However, the point where the interference causes the a disconnect will
also cause the Netstumbler receiver to hear garbage. You may not be
able to hear much with Netstumbler in the presence of interference.

Good luck.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
September 24, 2004 11:43:42 PM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in
news:uah8l01r52skukire4ao1sq07k18pntb2n@4ax.com:

>
> It might be interference. Judging by the general description it
> sounds like you might be near a cafeteria or establishment that
> runs microwave ovens almost continuously. We had a local market
> that effectively ran their sandwitch shop microwave oven
> erratically all day long. When it ran, wireless within about
> 1000ft radius was futile. I had to borrow a spectrum analyzer
> to verify. Eventually, I convinced them to clean the encrusted
> food off the door seal and life returned to normal.
Strong possiblity, there are lots of small shops close by.

> I don't think it's a cordless phone.
AFAIK cordless phones operate at 1880 - 1900 MHz and aren't allowed
in the 2.4GHz band.

>
> Another possibility are the new and disgusting metropolitan
> lans.
AFAIK very unlikely in the UK at this time.
>
> A variation on the theme are high powered central access points
> with highly directional and steerable antennas. The FCC
> considers these to be "point to point" instead of "point to
> multipoint" and therefore allows them to use additional power.
> If you happen to be badly located, these can be a major source
> of interference.
> http://www.vivato.net
Possible, but low probability.
Anonymous
a b F Wireless
September 24, 2004 11:46:23 PM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in
news:uah8l01r52skukire4ao1sq07k18pntb2n@4ax.com:

> How long is initially? Minutes, hours, days? If it's
> interference, duz it go away at night, or on weekends?
10 minutes or so - I suspect it was a fluke. No information available
(yet) re night or weekend conditions.
Anonymous
a b F Wireless
September 25, 2004 12:55:17 AM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> Yep. One clue I forgot to mention is the relationship between signal
> strength and S/N ratio. A sure sign of wireless interference is a

So, which is it Jeff?
Does Netstumbler see the noise generated by a microwave or not?

In my previous post, I certainly didn't mean to say that a microwave oven
would have an SSID of its own. I meant that there would be noise... that
red stuff on the Netstumbler display.

I see no change in the NetStumbler display when I operate a microwave oven
a few inches away.

Unlike some of the testing performed that I've seen referenced in the past,
which had things like warped doors, missing seals, bypassed interlocks, et al,
my testing was with two consumer grade microwaves in reasonably good condition.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
a b F Wireless
September 25, 2004 12:55:18 AM

Archived from groups: alt.internet.wireless (More info?)

On Fri, 24 Sep 2004 20:55:17 +0000 (UTC),
dold@XReXXOverc.usenet.us.com wrote:

>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>> Yep. One clue I forgot to mention is the relationship between signal
>> strength and S/N ratio. A sure sign of wireless interference is a

>So, which is it Jeff?
>Does Netstumbler see the noise generated by a microwave or not?

No. Netstumbler will not detect microwave oven noise. However, it
will detect the effects of microwave oven noise on a 802.11b/g data.
Remember, this one is bad enough to cause a disconnect, not just a
traffic slowdown. That will surely show up in the S/N ratio if it's
interference. If the access point or client radio doesn't have any
way to monitor signal strength or S/N ratio, then Netstumbler is a
good way to do it.

>In my previous post, I certainly didn't mean to say that a microwave oven
>would have an SSID of its own. I meant that there would be noise... that
>red stuff on the Netstumbler display.

Actually, I don't think (i.e. not sure) that the red stuff is actually
a measurement of the noise level. Methinks it's the error rate which
is an indication of the amount of interference. I'll do some digging
(later) to be sure.

>I see no change in the NetStumbler display when I operate a microwave oven
>a few inches away.

Huh? I certainly do. Orinoco Silver PCMCIA card talking to Linksys
BEFW11S4 router. If I'm playing streaming media or downloading files,
it stops dead as long as the oven is on. That's from about 15ft away.
I have some 802.11g radios and can try it with 802.11g to see if it
reduces the data rate. It should.

>Unlike some of the testing performed that I've seen referenced in the past,
>which had things like warped doors, missing seals, bypassed interlocks, et al,
>my testing was with two consumer grade microwaves in reasonably good condition.

Hey. That was my oven that had the warped door hinge. A dash of
leverage and judiciously applied brute force returned the hinge to
some semblance of it's originally designated position. It still leaks
a bit (according to my microwave oven leakage detector) but is well
within FCC limits. Incidentally, I can also "see" the effects of one
neighbors microwave oven and possibly 2 others.

Dueling with Microwave Ovens
http://www.wi-fiplanet.com/tutorials/article.php/311653...

Wi-Fi Interference
http://www.wi-fiplanet.com/columns/article.php/950691


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
September 25, 2004 1:56:56 AM

Archived from groups: alt.internet.wireless (More info?)

Frank le Spikkin <zaq@invalid.jp> wrote in
news:Xns956ED2DD6DD86FlSxxx@130.133.1.4:

> AFAIK cordless phones operate at 1880 - 1900 MHz and aren't
> allowed in the 2.4GHz band.
>

Correction: I intended to say:
AFAIK cordless phones *here in the UK* operate *at most* at 1880 -
1900 MHz and aren't *legal* in the 2.4GHz band.
Anonymous
a b F Wireless
September 25, 2004 8:40:28 PM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> No. Netstumbler will not detect microwave oven noise. However, it
> will detect the effects of microwave oven noise on a 802.11b/g data.

That sounds like doublespeak.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
a b F Wireless
September 25, 2004 8:40:29 PM

Archived from groups: alt.internet.wireless (More info?)

Some day we will have to arrange a Liebermann v. Dold faceoff! <grin>

--
Bob Alston

bobalston9 AT aol DOT com
<dold@XReXXOverc.usenet.us.com> wrote in message
news:cj471s$5l3$1@blue.rahul.net...
> Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>> No. Netstumbler will not detect microwave oven noise. However, it
>> will detect the effects of microwave oven noise on a 802.11b/g data.
>
> That sounds like doublespeak.
>
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
>


---
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Anonymous
a b F Wireless
September 25, 2004 8:40:29 PM

Archived from groups: alt.internet.wireless (More info?)

On Sat, 25 Sep 2004 16:40:28 +0000 (UTC),
dold@XReXXOverc.usenet.us.com wrote:

>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>> No. Netstumbler will not detect microwave oven noise. However, it
>> will detect the effects of microwave oven noise on a 802.11b/g data.

>That sounds like doublespeak.

You gotta work on the diplomacy angle. However, it's the Day of
Attonement and I'm suppose to be nice. I'll try again with a bit more
detail and fewer assumptions.

Netstumbler gets ALL its signal strength and S/N information from the
maangement frames of the devices that it hears. It does NOT measure
these by itself. Therefore, if you just fire up Netstumbler, but have
no access point or Ad-Hoc network nearby to supply these numbers, you
will see absolutely nothing on the nifty Netstumbler graphs.
Similarly, if you fire up a nearby microwave oven, Netstumbler will
again show absolutely nothing.

Next, we have Netstumbler pulling numbers from a nearby access point.
Signal strength is strong. Noise level graph is low. S/N ratio is
great. Life is good.

Now, we add a source of interference. It can be another active DSSS
radio on the same channel, a frequency hopping cordless phone, or a
microwave oven. It doesn't matter as long is it's in the same
frequency range. (I don't want to get into J/S jamming to signal
ratio here). The jamming causes Netstumbler to have a problem hearing
the access point and/or causes the access point to have a problem
hearing Netstumbler. Unless really severe, the effects of jamming
will not be noticeable on the signal strength graph. However, the
noise graph will show a substantial increase in noise, which in this
case I think (not sure) means the number of undecodeable packets.

Therefore, Netstumbler cannot be used to see, sniff, or direction find
a microwave oven or other source of interference. However, it can be
use to detect the effects of such interference on the signal to/from
an 802.11b/g access point.

I can probably simulate this at home and post Netstumbler screen
dumps. However, it's a holiday, my patch job on my trucks power
steering hose just failed (again), and I gotta do some billing.

Any questions?

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
September 25, 2004 11:15:10 PM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:

> Therefore, if you just fire up Netstumbler, but have no access point or
> Ad-Hoc network nearby to supply these numbers, you will see absolutely
> nothing on the nifty Netstumbler graphs.

I don't expect NetStumbler to be a general purpose RF detector.

> Now, we add a source of interference.
> ... the noise graph will show a substantial increase in noise

That's what I said.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
!