"Ellen MacArthur" wrote in message
reenews.net...
http://www.radiolabs.com/products/wireless/waverv.php
I'm looking for a good antenna for wifi on my RV for a laptop computer.
What do you think of this one?
It's got all the technical things there. Do they look good? Can it really
reach out four miles like it said in Cruising World
magazine?

Cheers,
Ellen


They put the radio modem under an 8 dB omnidirectional antenna and run the
data signal down the USB cable.

One way link budget:

Tx power = +26 dBm
Tx gain = +8 dB
Rx gain = +8 dB (assume receiver is same as Tx)

Receiver sensitivity = -93 dBm @ 1Mbps data rate.

Link can tolerate path loss of 26 +8 + 8 -93 dB = 135 dB


Friis Equation:

Path loss (dB) = 32.44 + 20 log (km) + 20 log (MHz)

PL (dB) = 32.44 + 20 log (km) + 20 log (2450)

PL (dB) = 100 + 20 log (km)

135 - 100.22 = 20 log (km)

1.73 = log (km)

55 km = Link range.

I think their quoted sensitivity of -93 dBm may be too high. For a 1 Mbps
data rate assume a slope factor of 2.3 so Rx bandwidth is approx 2.5 MHz.

Thermal noise power at 273K is:

P = kTB k = 1.38e-23; T = 273; B = 2.5e6 Hz

P = 9.5 fW

P = -110 dBm.

Doesn't look like thermal noise is a problem. The noise figure of the front
end is probably 2-3 dB so it should go 4 miles and beyond.

Go for it, you can always return it if it's a pig.