[MLB-WIRELESS] Client side access

[ABBENHUYS, Ryan]

Damnit!!! I had that idea quite sometime ago about using a long USB cable
and a USB adapter instead of using a long antenna cable!!!!

grrr, I knew I should have posted it to the list.

 
 -----Original Message-----
From: Richard Talbot [mailto:richardt at frontline.com.au]
Sent: Monday, 21 January 2002 15:45


Ok, some more testing was done on the weekend, this time with hardware
suitable for user (leaf) nodes.

We have noted several issues with the present method of, buying a Lucent
card, pigtail and 10-15m LMR-400 including:

Most users have desktops, necessitating a $120 investment on a PCI -> PCMCIA
adaptor. 
LMR-400 is not cheap and there is an appreciable investment involved to buy
it (around $120-$140 for a 10m cable) 
Pigtail cables are very lossy and expensive to boot.  The Lucent connector
alone is rated with a SWR of 1.56:1 at 2.4 Ghz, to say nothing of feedline
losses and poor construction techniques.

In short, Losses between the card and the antenna are high, as are the costs
involved in setting the whole thing up.

In our particular application there are bigger problems.  We are planning to
mount the Galaxy antenna on the roof, about 6-8 m up a TV antenna mast.
Common sense would kind of dictate that we are not going to run a 15-18m
length of LMR-400 to the office downstairs.  The smartest thing to do would
be to put an AP or a computer in the roof and run ethernet the rest of the
way.  In order to do this we are also going to need 10 m of feed line.  The
AP is also not to good as it is expensive and requires our neighbours to
have a card in infrastructurem ode.

We wanted to try another method.  The plan was to use a USB based card (in
this case the Dlink DWL-120).  These are cheap, easily modified and allow us
to run a simple USB cable up the mast.  The unit is smaller than a AP and
cheaper.

Our first job was to test the performance of the card as both of us had
heard they didn't go as well as a PCMCIA unit. T esting on a celeron 400
running win 2k and 64 mb ram, showed us downloading a 20Mb file from a local
ftp server at 470k/sec.  Not toos habby at all, so this was obviously worth
the trouble to test.  There may be an issue with USB being a bit slower than
PCMCIA, but will everyone really be running at 11Mb?

So far so good, the next question is, can we get into it?  This turned out
to be fairly simple.  The board is setup for easy access to the antenna
terminals.  We also found that the seconda ntenna is easily disabled and
connected to an external antenna.  This has some serious possibilities.  We
could run two antennas in diversity mode.  Due to the negligible amount of
additional coax, this is quitei nexpensive.  The whole lot can be mounted in
a waterproof box very close to the antenna feed point.

Having some surplus Galaxy's about we had an interesting idea.  What if we
put the card in front of a grid in about the same place as the dipole sits
in the feedhorn?  Some experimentation came up with a fairly predictable
result.  Approximately 13db gain on theo riginal signal levels.  With some
more accurate positioning and a fewm ods, I am sure this could be better.
So with some work we might not even need to open the box and take to it with
soldering iron.

Now the cabling.... It seems you can only run 5m of USB cable between two
devices.  That's a real shame because we were so close.  However, we found a
5m active USB cable advertised at www.ht.com.au .  Seems you can use this
with a simple 5m cable to do 10m.  You can use 4-5 of these things if you
really want to get 20-25m of USB.  We have seen prices elsewhere as low as
$30 / 5m cable.  So it works out about $6 per meter in cable.  Less than
LMR-400 and definitely less than the LMR-400 and the connectors for each
end.  The USB cables are definitely easier for the amateur to setup too.

The only remaining problem was that of ourP C.  We have some old 486's and
some low end Pa's that we want to use in the roof at each end.
Unfortunately no USB ports.  Nevermind www.ht.com.au has some USB dual port
cards for $29 and they work with Linux.  Much better than the $120 PCI ->
PCMCIA converters.

The testing continues and I'll keep you all posted.

Cheers
Richard


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