[MLB-WIRELESS] New world record for wifi link (125 Miles).

Adrian Lodders adrianlodders at bigpond.com
Wed Aug 3 16:09:43 EST 2005

Also I think the people that managed 125 miles went way over the legal
limit so I propose we attempt to break the "Worlds Longest Legal WiFi

I'll also submit the proposal to Guinness world records when ready but
will the record be under the name of MelbWireless or the people involved
or the people involved who are part of MelbWireless? I'd say the later
would be in order, myself.

Also here are the photos from the US 2004 attempt:

-----Original Message-----
From: owner-melbwireless at wireless.org.au
[mailto:owner-melbwireless at wireless.org.au] On Behalf Of Tony Langdon
Sent: Wednesday, 3 August 2005 4:00 PM
To: 'Dan'; 'melbourne wireless'
Subject: RE: [MLB-WIRELESS] New world record for wifi link (125 Miles).

> A 200mW Senao card in each laptop.  The Senao cards have two 
> antenna sockets, one is TX/RX and one is RX only.  The 200mW 
> Senaos have a better RX sensitivity than the 100mW versions, 
> and RX sensitivity is the key to breaking this record 
> legally.  We can separately pad down the TX level if we have to.

This makes sense.  Separating Tx and Rx had a few advantages.  At 200
mW, it
only takes 13 dB gain to hit the 4W EIRP limit, so an antenna with a
pattern can be used.  That makes the job of aiming the high gain Rx
at the other end much easier.  And it means if one has a 3m dish to put
the Rx end, it can be used without fear of exceeding the legal power
And it's then dead easy to install a preamp at the antenna to overcome
feedline losses there.
> The biggest dishes we can lay our hands on - one at each end 
> plugged into the RX-only socket of each Senao - this 
> maximises our receive gain.  It also makes our receiving 
> beamwidth as narrow as possible - this cuts down on our 
> received noise level.

Agreed.  And the Tx pattern is broad, making an easier target to aim the
high gain antenna at.

> A 13dBi antenna plugged into the TX/RX socket of the 200mW 
> Senao. 200mW = 23dBm 23dB + 13dB = 36dB which is the max legal EIRP.
> Possibly we could use a 14dB panel at both ends and claim a 
> 1dB loss through connectors and crappy cable. :)

Which is probably close to reality, though to split hairs, an accurate
strength meter should be used to very legal limits... ;) 
> Alternatively, a 16dBi antenna with a long enough run of 
> LMR-400 to create a 3dB cable loss.  I don't think the 
> beamwidth of the TX antenna is too important as it is the RX 
> antenna that has to sort the signal from the noise.

Actually, the broader the transmit beam, the easier it will be to line
everything up.  I'd go for as low gain as we need to hit the legal limit
(after connector losses).
> Kismet will be very important for antenna pointing.  Since we 
> will be running a TX and an RX antenna at both ends we will 
> need to line up each RX antenna separately. Kismet operates 
> by passive listening - without sending out beacons.  So we 
> can line up the RX antennas one at a time without needing to 
> have a fully symmetric link just to see each other.

Since the Tx antenna has relatively low gain, we should be able to point
within a few degrees of the actual direction and be within a dB or 2 of
maximum field strength in the desired direction.  This is the reason to
for as low gain as possible.  The Rx antenna will obviously need very
accurate pointing for this to work, due to its much higher gain.
> Aiming the big receive dishes that have such narrow 
> beamwidths will be tricky.  They'd definitely need to be on a 
> sturdy mount with precise pan/tilt control.  Being up on a 
> high mountain would probably mean lots of wind so you'd need 
> it anchored to something very heavy.

Yep.  That's for sure.

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