Alex <agarbino@gmail.com> hath wroth:
>I'm trying to transmit telemetry from a race car to a base station via
>802.11. It's mostly wide open terrain, but the range need is ~0.5
>miles, even 1 mile at some tracks. Is it possible to achieve this via
>802.11?
Barely, just barely. Some of the local drivers have tried Wi-Fi for
telemetry with mixed results. You can't install a directional antenna
on the vehicle and it's a pain to install a tracking dish antenna on
the other end. However, the real problem is that many tracks have
hills, buildings, and stands in the way, thus ruining the line of
sight. That means multiple access points. There are also technical
problems involving time it takes to switch access points, and doppler
shift. All are solvable, but kinda a mess.
> I've seen 27dBm transmitters (http://www.quickertek.com/
>Quicky.php), 12-15 dB omnidirectional antennas, but very scant info
>regarding the actual range achieved (because of variable conditions,
>etc).
A 15dBi antenna has a -3dB beamwidth of perahaps 5 degrees or less.
(It's 3am and I'm not going to look up the actual value). Even the
slightest tilt of the antenna will cause signal loss.
>I can put a laptop (or even PC) in the race car, and put an omni
>antenna if need be at both locations... but would it be enough?
I'll expound later on my personal experiences with laptops in
automobiles. Let's just say that nothing less than a Panasonic
Toughbook on shock mounts is going to survive for long. PCIe solid
state hard disk if you can afford it. See:
<http://www.mp3car.com/galleries.php>
for photos of how some do-it-thyself vehicular computer installations
were performed.
What you managed to leave out is what type and speed of data are you
planning to send? Speed and range are inversely releated. If you
don't need all the speed of Wi-Fi, you can get quite a bit of range
from other technologies. See the serial port versions of these
companies products. Look at 900Mhz, not 2.4GHz. You won't get much
thruput (perhaps 50Kbits/sec) but you won't need ultra high gain
antennas and your range.
http://www.freewave.com http://www.maxstream.net http://www.avalanwireless.com http://www.data-linc.com/wireless.htm http://www.moxa.com/Zones/Wireless_Ethernet/
(etc...) Search Google for "wireless serial", "wireless rs-233", and
"wireless ethernet". Mostly they're industrial products, with low
thruput, and fairly high prices compared to cheap wi-fi.
--
Jeff Liebermann
jeffl@cruzio.com
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Long range wireless 
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