antenna-theory.com

[tensor20]

RF cables suffer attenuations of various types. I was reading about wi-fi antennas, which work on the 2.4 GHz frequency. An RF coaxial cable connected to the antenna can have a maximum length of about 30 feet, I heard, after which the losses become too large....

The set up that was suggested was: wi-fi antenna and a bridge converter that transforms the signal from the antenna to an electrical signal that can travel on an Ethernet cable (twisted cable, CAT 5, CAT6)....An ethernet cable can be up to 100 meters long...why? Why does the ethernet cable suffer so little loss compared to the RF cable?

Thanks
tensor20

[Schubert]

All cables suffer attenuation, and this attenuation increases with frequency.

If the cable to the WIfi antenna carries a WIFI signal, it is 2.4 GHz (for 802.11b) or 5 GHz (for 802.11a).

CAT5 (ethernet) cables carry signals at much lower frequencies - I think it is less than 40 MHz, or maybe 100 MHz max. This is significantly lower frequency, and as such the attenuation per meter is much less.

Typically when ethernet is connected to a wifi router a low-frequency data signal is sent along the cable, and then the router modulates this data up to 2.4 GHz and then feeds it to the antenna. The same things happens on the download side, the 2.4 GHz signal received by the antenna is modulated down in frequency to the lower frequency (40 MHz or whatever) and then the data goes on its way.

[tensor20]

Thanks Schubert!

This is my scenario: there is an ISP that is sending a wi-fi signal towards my small town. The distance is about 3, 4 miles....
I am planning to place a wi-fi antenna on the roof. I have a single computer downstairs that is about 150 feet away. No need for a router or wireless. The computer can be hardwire.

As you are saying, 150 feet of RF cable would create to much loss. I need something to convert the 2.4 Ghz signal to an ethernet signal, and take an ethernet cable from near the antenna to my computer...
What device would do that, i.e. convert the 2.4 GHz signal to an ethernet signal?
Is the device called a bridge? That is a generic term...

I found these schematics online:

http://www.ccrane.com/instruction-manuals/wifi-bridge-kit-connection-diagram.pdf[url]

I would be the client house in the diagram...

Thanks,
tensor20[/url]

[Schubert]

I don't understand. You want to run an antenna signal straight into your computer? I'm not sure that makes sense.

What I would do in your situation is probably take a simple wireless router, and hack it to run your big antenna directly into it. Then the received wifi signal will go straight into the router, which will output the ethernet, which can then be run directly into your computer.

[tensor20]

Sorry for the confusion:

so I have a single computer. An ISP is broadcasting, from 4 miles away, a wi-fi signal, to my town.
I am trying to understand what equipment I would need to catch that wi-fi signal and get the internet connectivity.

To catch the signal I need a wi-fi antenna (dish, yagi, planar).
A coaxial cable is attached to the antenna. The coax cannot be too long or too much loss will occur.
A device that converts the wi-fi signal to ethernet signal would be needed so that I can run 40 meters of ethernet cable directly to my computer and surf the internet...

thanks
tensor20