5 km Range Commercial Wi-Fi Available

prostoalex writes "Japanese company Maspro Denkoh will start selling transmission systems, enabling WiFi signal over 5 km, Network World magazine reports. From the article: "There are two types of antenna: one is a tube-shaped model about 40 centimeters long, and the other is a much shorter and square-shaped model. Combining two of the tubular antenna -- one on each end of the link -- will result in a transmission distance of about 5 kilometers while one of each antenna will work on distances up to 2 kilometers and two of the compact antenna will be fine for up to a kilometer, the company said.""

Comments

What would the FFC do?

[Brent Spiner]

If this was $5,230 cheaper, and if the FCC wouldn't come after me with a sawed-off shotgun, I'd probably get one of these.

Anyone surprised?

[DeadBeef]

This is just a random press release from a company selling boring old wireless kit. There isn't anything special about getting 5km of range with off the shelf wireless gear,

If anyone cares the math is not that hard to follow:

You take the transmitter output power, subtract any loss in the cable between the transmitter and the antenna, add the gain of the anteana. http://db.osoal.org.nz/eirp-calculator.html

Then you have to subtract the free space loss of your path ( the loss you get by putting the signal across the air ): http://db.osoal.org.nz/freespace-loss-calculator.h tml

And finally you add the recieve gain of the receiving antenna, subtract the loss from the cable on the recieving end and compare with the receive sensitivity of your wireless receiver. I have bundled the rest of the calculation into this bit of javascript.

For example, if I have two 2.4ghz radios that output 15dbm (32mw) that have a recieve sensitivity of -83db that are in waterproof boxes on the antenna mounting connected to two 22db antenna's 5km apart very roughly.

15db - 1db + 22db = 36db or ~3981mw (just under the 4 watt max).

- 121.65db for our free space loss

+ 22db - 1db = -64.65

-64.65 is the strength of the signal received at the other end, fortunately the receiver has a receive sensitivity of -83 so we are in business. There is a link margin of ~19db to account for a little bit of noise, fade, solar flares, alien abductions etc.

If you want more range, increase the power of the transmitter or the gain of your antenna. The government limits ( 4 watts for 2.4ghz, 250mw for 5.3ghz and 4 watts for 5.8Ghz in New Zealand ) are going to determine your maximum range barring some magical new wireless gear that has a better receive sensitivity.