which wireless router?

Nils Kassube kassube at gmx.net
Tue Feb 26 07:37:45 GMT 2008


Billie Walsh wrote:
> Larry Hartman wrote:
> > It has been 
> > pointed out to me along the way that if two antennas are operating at
> > the same frequency at the same time, that when they are a given
> > distance apart, the signal strength perpendicular to the axis of the
> > two antennas greatly increases, while the signal strength along that
> > axis reduces.

That is correct, as long as you have equal cable lengths between the 
transmitter and the two antennas. The best distance would be multiple of 
0.5 wavelengths.

> > This theory is why truck drivers employ two antennas for their CB's. 
> > In their example the typical width of a tractor cab is about the
> > right width necessary for signal strengthening in front of and behind
> > the truck.  As was explained to me, the improvement can sometimes be
> > measured in terms of miles.

Nice idea - the distance would be 5.5 m.

> > Depending on the electronic environment, the employment of two
> > antennas may not always generate interference, but may be
> > complimentary.

The term is still "interference", constructive interference in 
forward/backward direction and destructive interference to the sides. See 
<http://en.wikipedia.org/wiki/Interference>.

> > Dunno about Linksys or any other vendor, but it is a 
> > consideration.
>
> Considering the difference between 27MHz, CB frequency, and the 2.4GHz
> of wifi the spacing on a Linksys may be just about the equivalent
> distance.

Sure, that could be done at the WLAN frequencies as well, but then the 
antennas would have to be fixed and mechanically parallel. However, you 
can rotate the antennas in 2 axes and the distance is not right. While 
you could compensate for the distance with the cable lengths, I don't 
think the antennas are connected in parallel. The distance of the 
antennas is 0.15 m, which is 1.25 wavelengths. For antennas in parallel 
it would be more useful to have a distance of 1 or 1.5 wavelengths. But 
the distance is best suited for diversity reception. With a given 
distance of 1.25 wavelengths, if one antenna is in a position of 
destructive interference, the other antenna usually is in a position of 
constructive interference.


Nils



More information about the kubuntu-users mailing list