Weird interference discovered

mcr

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My wi-fi connection intermittently dropped to almost nothing. This
annoyance occurred seemingly randomly and infrequently. It did occur
enough to be irritating, so I checked around the house for things that
could cause this behavour. I dont have a microwave or a cordless phone
so I was stumped.

Then today the neighbour in the apartment/flat opposite received cold
callers (as did I) when I noticed it was her 'wireless' doorbell that
was causing the connection drop. Weird, but true.

Amazingly she agreed to change it to a wired one, on provision I paid
and fitted it. I cant argue with that. I find it amazing that that was
the cause of the problem. I tried it a number of times and sure enough,
each time I pushed the doorbell, the connection was lost.
--
MCR
MAME - History In The Making
www.lazarus.org.uk
www.pleasuredome.org.uk
 
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On Fri, 25 Jun 2004 10:11:58 +0000 (UTC), MCR
<mcr@nospamtombstones.org.uk> wrote:

>My wi-fi connection intermittently dropped to almost nothing. This
>annoyance occurred seemingly randomly and infrequently. It did occur
>enough to be irritating, so I checked around the house for things that
>could cause this behavour. I dont have a microwave or a cordless phone
>so I was stumped.
>
>Then today the neighbour in the apartment/flat opposite received cold
>callers (as did I) when I noticed it was her 'wireless' doorbell that
>was causing the connection drop. Weird, but true.
>
>Amazingly she agreed to change it to a wired one, on provision I paid
>and fitted it. I cant argue with that. I find it amazing that that was
>the cause of the problem. I tried it a number of times and sure enough,
>each time I pushed the doorbell, the connection was lost.

Amazing. Most wireless doorbells run on 433.925, 418, and 315MHz with
single carrier OOK (on-off keying). I'm not familiar with UK models.
It should not have substantial harmonics in the 2.4GHz region and
those should not have a noticeable effect on 2.4GHz traffic. To the
best of my knowledge, there are no Wi-Fi wireless doorbells.

Was this doorbell perhaps part of some Wi-Fi connected burglar alarm
system?

Could I trouble you for the model numbers of the doorbell and wireless
router/bridge? I'm more interested in the router/bridge being
affected. I guess(tm) that perhaps the CCA (clear channel
assessment) feature of 802.11g is overly sensitive or easily confused.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D 831-336-2558
Santa Cruz CA 95060 AE6KS
 

mcr

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Jeff Liebermann wrote:
Snipped


> Amazing. Most wireless doorbells run on 433.925, 418, and 315MHz with
> single carrier OOK (on-off keying). I'm not familiar with UK models.
> It should not have substantial harmonics in the 2.4GHz region and
> those should not have a noticeable effect on 2.4GHz traffic. To the
> best of my knowledge, there are no Wi-Fi wireless doorbells.

Well I am sure they dont interact on the same frequency also.. That is
why it isnt one of the things that I was troubleshooting to begin with.

I would say that the doorbell was at fault in this case rather than my
router...

> Was this doorbell perhaps part of some Wi-Fi connected burglar alarm
> system?

Not AFAIK. I dont know the details yet, but when I 'buy' it for another
I will post the details. She works in B&Q (Superstore) so it is
reasonable to assume it is one of their home brand ones.

> Could I trouble you for the model numbers of the doorbell and wireless
> router/bridge? I'm more interested in the router/bridge being
> affected. I guess(tm) that perhaps the CCA (clear channel
> assessment) feature of 802.11g is overly sensitive or easily confused.
>

The router is A 2wire 233 router with a PCMCIA Wi-Fi card on the front
(2wire branded).
The channel is set to 6 (Default). It's 802.11b btw.#



--
MCR
MAME - History In The Making
www.lazarus.org.uk
www.pleasuredome.org.uk
 
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On Fri, 25 Jun 2004 18:16:02 +0000 (UTC), MCR
<mcr@nospamtombstones.org.uk> wrote:

>Well I am sure they dont interact on the same frequency also.. That is
>why it isnt one of the things that I was troubleshooting to begin with.

I just happen to have a wireless doorbell here. 433.925MHz. No
manufacturer name or model visible. I looked at it on my antique
HP141 spectrum analyzer and it was clean with almost no harmonics.
My guess is a SAW (surface accoustic wave) oscillator which is rather
clean in output. I haven't pryed it open yet. Does not affect my
home router (Linksys BEFW11S4) as far as I can tell. You're might be
different.

>I would say that the doorbell was at fault in this case rather than my
>router...

The first step to solving a problem is not to assign the blame. If
there are any other wireless routers available in the building, it
would be interesting to check if they are similarly affected. Same
with additional wireless doorbells. It's possible that doorbell
transmitter might be defective and unique by oscillating in the 2.4Ghz
band. I've seen stranger sources of spread spectrum intereference
(GPS vs TV amplfier):
http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=43404
and susceptibility issues such an unfiltered wireless receiver front
end with a truely horrible 20 or 30dB dynamic range which would
overload on almost any RF signal, regardless of frequency. Don't
assume it's the doorbell until you're sure it's not the 2wire router.

>The router is A 2wire 233 router with a PCMCIA Wi-Fi card on the front
>(2wire branded).
>The channel is set to 6 (Default). It's 802.11b btw.#

That eliminates the possibility of an 802.11g related CCA problem.

Hmmm... are you able to use a different wireless card in the 2wire
router? If so, that might be worth trying.

I agree. Wierd.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D 831-336-2558
Santa Cruz CA 95060 AE6KS
 
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Archived from groups: alt.internet.wireless (More info?)

6th harmonic of the 418 MHz range in close proximity (" the neighbour in
the apartment/flat opposite")...
N9TGW
"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
news:bggod09fvncq114m675jq8irvn7jjjvnpl@4ax.com...
> On Fri, 25 Jun 2004 10:11:58 +0000 (UTC), MCR
> <mcr@nospamtombstones.org.uk> wrote:
>
> >My wi-fi connection intermittently dropped to almost nothing. This
> >annoyance occurred seemingly randomly and infrequently. It did occur
> >enough to be irritating, so I checked around the house for things that
> >could cause this behavour. I dont have a microwave or a cordless phone
> >so I was stumped.
> >
> >Then today the neighbour in the apartment/flat opposite received cold
> >callers (as did I) when I noticed it was her 'wireless' doorbell that
> >was causing the connection drop. Weird, but true.
> >
> >Amazingly she agreed to change it to a wired one, on provision I paid
> >and fitted it. I cant argue with that. I find it amazing that that was
> >the cause of the problem. I tried it a number of times and sure enough,
> >each time I pushed the doorbell, the connection was lost.
>
> Amazing. Most wireless doorbells run on 433.925, 418, and 315MHz with
> single carrier OOK (on-off keying). I'm not familiar with UK models.
> It should not have substantial harmonics in the 2.4GHz region and
> those should not have a noticeable effect on 2.4GHz traffic. To the
> best of my knowledge, there are no Wi-Fi wireless doorbells.
>
> Was this doorbell perhaps part of some Wi-Fi connected burglar alarm
> system?
>
> Could I trouble you for the model numbers of the doorbell and wireless
> router/bridge? I'm more interested in the router/bridge being
> affected. I guess(tm) that perhaps the CCA (clear channel
> assessment) feature of 802.11g is overly sensitive or easily confused.
>
>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D 831-336-2558
> Santa Cruz CA 95060 AE6KS
 

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