> WN3J wrote:
No, it was WN3A that wrote that. A as in "agitator" :-)
> >It wasn't until car
> >radios with vertical whip antennas started to gain
> popularity did vertical
> >polarization start to become important, and CP resulted as a
> solution to
> >satisfy listeners using either horizontal or vertical antennas, while
> >improving multipath performance as a side-benefit. Of course
> this also
> >meant that broadcasters needed 2X the transmitter power, or
> 2X the number of
> >antenna bays, to achieve the same amount of ERP, to convert
> from H to CP.
>
> Actually, as I wrote, the opposite is true. CP give MORE
> multipath than linear polarization.
CP affords more/less opportunity for reflection as compared to linear
polarization only if the reflecting surface of the object is appreciably
small in one plane (H or V) as compared to the other. A flagpole obviously
would make a poor H reflector. A mountain is going to reflect V or H
equally well, as will a tractor-trailer passing you on the highway.
> CP gives higher average
> signal strength but a lower _quality_ signal. This is
> especially hard on an FM-stereo signal, which is even more
> susceptable to mulitpath distortion than an FM-mono signal.
This is primarily a function of bandwidth, and to a somewhat lesser degree
the way FM multiplex is done. A wider bandwidth signal will inherently have
a greater chance of having "slope" across the modulation bandwidth caused by
multipath. Left uncorrected, as it typically is in broadcast FM receivers,
it can be problematic.
> So there's the trade: more average signal strength but more mulipath.
> (Did you know that when various systems for broadcasting
> FM-stereo were evaluated, the system which used FM for the
> stereo subcarrier was rejected due to greater upset by
> multipath than the AM subcarrier system that was ultimately chosen.)
Yes, but from what I remember, the FM system had better performance under
weak signal conditions than supressed-carrier AM. It was wider too.
> I think that CP would work well on an amateur radio repeater.
> The increased average signal strength (there's more
> uniformity of signal strength as well in a moving vehicle).
So why is it that you believe CP would be "a good thing" for a VHF repeater,
but it's "a bad thing" for VHF broadcasting (if I'm reading you right)? The
bandwidth issue, or something else?
--- Jeff WN3A
