Why twin antennas on wireless routers?
Why twin antennas on wireless routers?
(OP)
Most wireless access points and routers have twin antennas on the rear. What's the reason behind this? And if you're trying to extend the range of the wireless link by using an external directional antenna, which antenna port do you use, or does it matter?
RE: Why twin antennas on wireless routers?
I'm sure you've noticed that when listening to FM in your car, there will be locations where you need to pull ahead a few inches to have good reception. In fact, the process becomes nearly automatic where you always leave a slightly larger space in front of your car at those intersections in case you need to roll forward a quarter wavelength.
Twin antennas provides similar 'space diversity' to avoid nulls. If one antenna is in a null, then the other won;t be.
RE: Why twin antennas on wireless routers?
RE: Why twin antennas on wireless routers?
Leave a whip antenna on the second port just in case it helps. In any case, it would likely be better than leaving the second port open circuit.
If you run into any difficulties, then swap ports (directional <-> whip).
I wonder how much antenna gain I would need to tap into the free WAN that is about 10km up the road...
RE: Why twin antennas on wireless routers?
RE: Why twin antennas on wireless routers?
Wireless communication range/distance is reduced often by a factor of 2-6 due to multipath and normal range calculations get difficult/impossible.
Assuming that your wireless communication doesn't have multipath and is 500 feet with normal zero dBi antenna gains, everytime you double your distance you need 6 dB (factor of 4) more antenna gain in your receiver to keep the same signal strength. 10 km is 6 miles = approx. 30,000 feet. So to see how much extra gain you need, here is some basic math.
dist (feet) vs. antenna gain (dBi)
500 = zero (original antenna having 500 foot range)
1000 = +6
2000 = +12
4000 = +18
8000 = +24
16000 = +30
32000 = +36 dBi gain or 4000 gain.
Gain = 40,000/[(beamwidth azimuth) x (beamwidth elevation)]
or beamwidth = sqrt(40,000/4000)= sqrt(10)= 3.3 degrees.
at 2.4 ghz wavelength = 11.803"/2.4 = 5 inches.
3.3 degree beamwidth is approx. 20 wavelengths, so your antenna would be about (20x5")or 100" x 100" in size. That's pretty big.
KCH.