> Well, just turn your 2m handie talkie even with a rubber
> ducky on its side & note the drop in signal strength. Cross
> polarization losses, e.g. linear V to linear H (or vice
> versa) can be up to 30 dB!
In the absence of multipath, or more correctly, obstructions causing
reflections that cause polarization distortion/scattering, yes, you will see
typically 20 dB or more of cross-polarization loss if you were to use a Hpol
receive antenna to receive a Vpol transmission. That's why FM broadcasters
use CP - so that both "home" listeners using a horizontal wire dipole
connected to their stereo, or a roof-mounted yagi or turnstile, can receive
Hpol, and mobile listeners with a fender-mounted vertical whip can receive
Vpol. If they were to choose one over the other, the other half of their
audience would take a 20 dB hit (multipath issues notwithstanding).
In many congested areas of the US, such as here in the northeast, your
coverage is "interference limited". So, even if that 20 dB reduction in one
polarization might have still yielded an acceptable signal level under
"quiet" conditions in the absence of co-channel or adajacent-channel
interference, we don't have that luxury in the real world here. The
listener will suffer that 20 dB increase in U/D (undesired-to-desired
signal) ratio. So, here in the ever-competitive US, there's rarely a case
to be made for NOT running CP.
Translators are also used much more effectively in Europe, as is RDS/RDBS.
They're used in combination to fill in holes and to yield a multi-frequency
network, frequency-hopping your car radio automatically as you drive around
the countryside. Almost a cellular approach. In the US, we go for big
signals and maximum range. Just a different philosophy.
Quantity counts here.
> The BBC and the Deutche Bundespost are very picky about
> broadcast quality, much more so than the FCC (I speak from
> personal observation having lived in EU for years).
Yes, I know. We can talk about ITU-R 412, Eureka, iBiquity, and lots of
other things separate "us" from "them", but the topic started with how/why
CP was different/better than linear, how/why it was used on FM in the US,
and how/why some FM stations uses more or less H versus V.
Viva America! God save the queen!
--- Jeff WN3A
