[Cu-wireless] update; thoughts on radios, experiments, parts

[David Young]

We discovered Sunday that our Pringles can antennas are most
certainly polarized. If we orient our antennas carefully, we can send
cross-polarized signals on the same channel through the same space
without interference.  Yum.

We are able to reach Maiko's porch (especially the western wall) with
S/N of up to 30dB. Yahoo.

Word is that the Cisco Aironet 350 radios are most powerful (100mW vs.
30mW for Lucent/Agere cards and the DWL-520). Also, Peter Folk tells me
you can lower their power level (using `ancontrol' in OpenBSD---there must
be a Linux equivalent). Prof. Kumar had told us that this was possible,
but this is the first time I've heard you can make the adjustment using
non-proprietary drivers.

I think that the usefulness of a 100mW transmitter is pretty clear. But
what might not be so clear is that adjusting power levels is really
useful, too: you can set up nodes to "whisper" to their nearest neighbors,
"shouting" only to reach far-off nodes. This is the way that Kumar's
research group uses them.

Cisco's model AIR-LCM352 has no built-in antenna, but two MMCX connectors.
This is advantageous, too, because it eliminates the radio leakage we
get with, say, the Lucent cards, whose diversity antennas we cannot
disable without modifying the cards.

So I am more and more excited about the Cisco cards. They are expensive,
though. The AIR-LCM352 costs $105.

Today UPS delivered the replacement for the pigtail that broke in transit.
Is it Zach's? Sascha's? I don't remember.

I am starting a new list of pieces we need. We should probably buy these
in pairs:

  T connector: 2 N-female to 1 N-male
  T connector: 1 N-female to 2 N-male

Also, for Pringles can antennas, we need N-female bulkhead mounts.
We have used three of Peter's, which we should replenish.  So what do
you think? Six of them?

We should try to build a coffee can antenna. I have an (annotated?)
Web page on the subject, sent to me by one John Glenn of Sidney.
Presumably it is not John Glenn, the astronaut. Incidentally, it tells
where to buy those bulkhead mounts.

Dave

On Mon, Mar 25, 2002 at 03:18:03PM -0600, Zachary C. Miller wrote:
> If we have 2 antennas mounted on a mast pointing in 2 different
> directions and they operate on 2 different channels can we combine
> their signals into a single coax run to the computer with 2 wifi cards
> and then put a splitter at the computer end with 2 pigtails? This
> could save some money and hassle (especially if we work to put in good
> coax installs at some houses for a single antenna and then decide to
> add a second antenna later...we don't have to run new coax, just throw
> on a combiner/splitter pair).
> 
> What do the theory heads think about this? Can signals for 2 channels
> from 2 antennas coexist on the same coax without significant loss?
> 
> -- 
> Zachary C. Miller - @= - http://wolfgang.groogroo.com/
> IMSA 1995 - UIUC 2000 - Just Another Leftist Muppet - Ya Basta!
>  Social Justice, Community, Nonviolence, Decentralization, Feminism,
>  Sustainability, Responsibility, Diversity, Democracy, Ecology
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-- 
David Young                   On the Job Consulting
dyoung at onthejob.net     Urbana, IL * (217) 278-3933