which wireless router?

Larry Hartman larryhartman50 at vzavenue.net
Tue Feb 26 14:03:28 GMT 2008


On Monday 25 February 2008 11:37:45 pm Nils Kassube wrote:
> 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

hmmm.



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