Long range wireless


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? I've seen 27dBm transmitters
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12-15 dB omnidirectional antennas, but very scant info regarding the actual range achieved (because of variable conditions, etc). 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?



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Alex hath wroth:

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.

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'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:

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.

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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.

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Jeff Liebermann

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