Re: Wireless stability when signals are TOO strong?

"Ken Bessler" <kg0wx@xxxxxxxxxxxxxxx> hath wroth:

I read (I think in the firmware for DD-WRT) that you should
never change the firmware over a wireless connection due to
the "inherent instability" of a wireless connection. Fine.

Sigh. There's nothing unstable about the wireless connection. What
happens is that during the firmware upgrade process, the wireless
connection is often disconnected by the running firmware. When that
happens, the firmware upgrade is aborted and does not complete. This
does not happen with the wired ethernet connection, which is why
firmware upgrades should always be done via a wired connection.

There are some people that have mentioned that they have successfully
upgraded the firmware via wireless. I've also done it successfully.
However, I've also done it via wireless by accident, when I had BOTH a
wired and wireless connection running from my workstation. It died
near the end leaving me with a mess.

I was web browsing the other day and it was acting like I had
a poor WiFi connection - I was re-loading webpages, re-submitting
forms, etc. Remembering the DD-WRT warning, I decided to
switch to my wired connection. Sure enough, things were better.

Sounds like interference from another wi-fi system on the same
channel.

I normally would assume this is normal but in this case the
distance between my laptops high gain antennas and my WRT54G
(v4) router was only 12".

That's a bit close. It's been a while since I've measured the
overload point on the WRT54G. I vaguely recall around -10dBm. You'll
probably get that at about 1ft antenna to antenna separation.

Could I be overloading my radios? Both my Atheros mini PCI
card and the Linksys router are set to 100mw and both have
dual external high gain antennas (7dbi on the laptop and 9dbi
on the router).

Yes. Lets do the math and calculate the minimum range (so that I have
an excuse not go do the laundry). It's exactly the same as the link
calculations. See:
| http://en.wikibooks.org/wiki/FAQ_for_alt.internet.wireless/Wi-Fi#Link_Calculations

TX power = +20dBm (100mw)
TX coax loss = 0
TX ant gain = 9dBi
Distance = unknown
RX ant gain = 7dBi
RX coax loss = 0
RX sens = -84dBm (at 12Mbits/sec)
Fade margin = Not needed here
RX signal = -10dBm (overload point)

Plugging this mess into:
http://www.terabeam.com/support/calculations/som.php
and trying various values of distance until the RX signal level is
approximately -10dBm. I get a distance of 0.0012 miles or 6.3 ft.
We're getting into the near field area so this number is at best a bad
guess, but it should give you some idea of where the problems will
start. 1 ft is much too close.

I'll see if I can find the magic number for the WRT54G overload point.

So, is this overload or is wireless just that unstable?

My seismograph shows no earthquake activity, so I guess it's stable.

--
Jeff Liebermann jeffl@xxxxxxxxxxxxxxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.

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