--- On Mon, 8/24/09, Jeff DePolo <j...@broadsci.com> wrote:
From: Jeff DePolo <j...@broadsci.com>
Subject: RE: Re: [Repeater-Builder] Diversity FM reception
To: Repeater-Builder@yahoogroups.com
Date: Monday, August 24, 2009, 9:32 PM
> Yes, CP does cause more multipath esp. in urban
>environments.
> Turns out there are a large number of buildings the
> preferentially reflect V better than H. CP gives V energy
> othwise lacking (mostly) in a strictly H xmt situation.
>I refer to another post I just sent, and I tie in another concept. If the
>reflecting surface is large enough, it's going to reflect both V and H
>?components. At VHF and UHF frequencies, any building of appreciable >ize s
>going to reflect both. A typical urban environment comprised of
>dozens/hundreds of large buildings is going to bounce around enough Vpol >and
>Hpol energy to cause multipath no matter what the originating station >was
>transmitting, H, V, or C.
>Any surface that is anything other than a perfectly flat plane is going to
>cause distortion of the incoming wave, distorting/skewing the >polarization..
>And when it comes to Cpol, the polarization sense is flipped when it is
>reflected, RHCP becomes LHCP and vice-versa. So, suffice it to say, when
>you're talking about reflections in an urban environment, or a mountainous
>region, or in reality, just about anywhere other than in the flatlands >with
>no nearby obstructions (farmhouse with a nice yagi on the roof), you may >as
>well assume you've got mulitpath comprised of a mix of polarizations.
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!My data comes from 35 years of
reported research in N.A. and Europe. I'm simply reporting what their research
found.
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). Additional data is from IEEE journals on the subject.
Amateur experience is from 'The Practical Handbook of Amateur Radio FM and
Repeaters' by Bill Pasternak, WA6ITF, and Mike Morris, WA6ILQ, published by
Tab Books. (There may be other amateur sources as well; if anyone knows, pse
let me know.)
>> Neither the BBC or the Germans use CP in FM broadcast, strictly H.
>And they also don't have the FCC, but we won't get into that....
>> TV tried & abandoned CP due to ghosting.
>Well, I wouldn't say that. One of the local high-power UHF stations,
>relatively high in the band, replaced their antenna about 10 years ago, >and
>went to CP. Their coverage noticibly improved. I live about 15 miles >from
>the transmitter and saw quite an improvement.
>One of our contracts is with one of the new nationwide 700 MHz services >that
>broadcasts digital mobile TV subscription services. Subscribers >receive on
>cell phones with extendable whip antennas. Those can be >oriented in any
>position, but would typically be held vertically. Guess >what polarization
>they're using?
Tell & we'll both know! My comments only apply to analog TV. UHF experience
with CP may be different than VHF.
--John
