Simple question on how satelite and wireless work

[@md0Cer]

I was wondering how some of these wireless technologies work in terms of the signal return.

Lets say for example I build a massive antenna for my 802.11b that transmits 8 miles, or have a satelite. If BubbathepersonwhoImadeup sends me an instant message, the antenna or the satelite beem it to my computer. Now if I send data back, how does it reach the antenna/satelite? You would need something with equal power for it to go back right? A pringles cantenna may be able to send wireless a few miles, but can the crappy little wireless PC card in a laptop send signals back those few miles? Or even send it into space to a satelite?

Bassically, I am pretty confused how these long range wireless solutions can receive data.

Thanks in advance to anyone who can clear this up for me. :) :thup:

[Kendan]

I think you are forgetting about a piece of the puzzle. for long range 802.11 you would use an AP at each location with a lot better than stock antenna on each AP. The Linksys WRT54G are used for this a lot now because of the third party firmware that gives it a lot of extra abilities (www.linksysinfo.com for more info)

Satelite internet has a dish and a Modem that connects to the sattelite and has a good bit of lag. I know they used to use a phone connection for the upload and the sattelite for the download. I am pretty sure this has changed.

[Barret]

Yes, with satalite you can now pay extra money and have both, upload and download, go quickly...

[@md0Cer]

Ah interesting! That clears it up. Thanks guys.

[nebben]

802.11b uses extremely low power equipment. I don't think anything is over 1w transmission power. Sheet, I think my AP is only like 500mw or less.

2way satellite uses higher power to transmit into space. Forget about a cantenna- the range is 20k+ miles. You are supposed to be a certified professional (certified by FCC) as far as I know if you are setting up a 2way satellite in the US. Because of the extreme distance your signals have to travel (20k+ up, and 20k+ down, then processed to the internet), latency can be awful, and not suitable for speedy things like VoIP and internet gaming. 802.11b based setups can be laggy too, but that might be because someone botched the configuration of the equipment, not because of the radio waves not being fast enough. 802.11b can be extremely low-latency. b00ya.

BTW- you may want to get a higher end antenna than a pringles can if you're aiming at 8 miles. I built a cantenna out of a Hunts pasta sauce can (gross sauce), and haven't got that far. Commercial grade antennas aren't hard to get- they're just extra $$.

-ben

[elfiena]

i have posted on another thread on how antannas work (http://www.ocforums.com/showthread.php?t=385344).

as for signal power output, FCC regulates it, so you really couldn't output more power. however there are other ways to get around that. for example, you can strengthen the wifi signal internally. after the antanna recieve the signal, you can pretty much do what ever you want with it include boost it with additional power. basically

[antanna]---[signalbooster]---[reciever]

however this configuration also boosts distortions, background noises, crosstalk etc etc. this is why people use directional antanna to modulate the shape of your output signal in order to get around of the distance limitations opposed by a standard in power output.

size of the antanna have a little to do with your signal quality. you can build a huge dish like the ones SETI uses to recieve wifi signals, however, wifi signals fizzle out over distance and there are other people using wifi as well which will result in interference. yes, your antanna can pick up the signal, the questions would be, is it the exact same signal being sent by the original host? and what performance do you gain from having a huge antanna?

size of the antanna also have little to do with transmission. a can-yagi would outperform a large dish with the same amount of signal power output. we are so used to having "one antanna does all" model that we hardly utilize strengths and weaknesses of different types of antanna.

best way to pass around a signal over long distance, is to modulate signal transmission through a yagi, while modulate recieving signal using a large dish and perhaps add a noise canclation + signal booster on the line between dish and reciever.

[JigPu]

Lets say for example I build a massive antenna for my 802.11b that transmits 8 miles, or have a satelite. If BubbathepersonwhoImadeup sends me an instant message, the antenna or the satelite beem it to my computer. Now if I send data back, how does it reach the antenna/satelite? You would need something with equal power for it to go back right? A pringles cantenna may be able to send wireless a few miles, but can the crappy little wireless PC card in a laptop send signals back those few miles? Or even send it into space to a satelite?
To use an analog from more common knowledge, think of a simple paper-cone megaphone.

A megaphone acts as a directional "antenna" of sorts for sounds. When you speak into the small end, the direction the sound waves go is restricted by the megaphone. You can thus be heard farther, because more sound energy is going in the direction of your listener (instead of going straight up or behind you, etc). The same can be said of a transmitting parabolic dish -- radio energy directed at the dish is all reflected off in a single direction. More radio energy reaches the recipient of the transmission, since less is being directed in some other direction.

Now, if you put the megaphone next to your ear, you will be able to HEAR farther as well. While the sound energy that reaches your ear is the same (since the person talking isn't talking any louder, and they aren't directing their speech at you with a megaphone), the megaphone has the effect to REMOVE sounds from other directions. Instead of trying to hear a tiny signal amongst the noise from all directions, you try to hear a tiny sound amonst the noise from only one direction. Since there will be less noise approaching you from only one direction, the signal you're trying to hear makes up a larger portion of the total sound energy recived. Again, this is analagous to a dish in that ONLY radio energy which is directed directly at the front of the dish will be recieved. Your tiny dipole antenna 8 miles away will be a much larger portion of the signal recieved now, and so be easier to pick out from the rest of the noise.

The same principle applies to all direcitonal antennas (not just dishes), though dishes are the easiest to visualize (since they concentrate radio energy in a way that is easy to see).

JigPu

[@md0Cer]

Ah thanks a bunch guys. That certainly does clear it up.