[opendtv] Re: Circular, elliptical antenna polarization improves mobile DTV reception reliability, says Schadler

Mark,

 

I notice that you (correctly, I believe) did NOT make a reference to “circular” polarization in your reply.  Should these types of transmissions be referred to as “dual” polarization, or is there any attempt (or need) to phase the emissions to create a true rotating polarization?

 

Most people seem to mean “dual” when they say circular with regard to this topic.  I’m curious about this.  Lacking a circularly polarized receiving antenna, is there any advantage to true circular polarization with I digital signal?  You can’t see the ghosts anymore to help you orient the antenna.  What do you think?

 

Thanks,

 

Ken Hunold

 

From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On Behalf Of Mark Aitken
Sent: Friday, April 22, 2011 7:19 PM
To: albert.e.manfredi@xxxxxxxxxx; opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Circular, elliptical antenna polarization improves mobile DTV reception reliability, says Schadler

 

Yes. Power is designated based on horizontal, and one may choose to ADD up to 100% into the vertical component. So, one would require 2x xmit power with full CP.

Mark A. Aitken
Director of Advanced Technology
Sinclair Broadcast Group
(443) 677-4425 Mobile
(410) 568-1535 Desk

Connected by DROID on Verizon Wireless

-----Original message-----

From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
Sent: Fri, Apr 22, 2011 21:32:26 GMT+00:00
Subject: [opendtv] Re: Circular, elliptical antenna polarization improves mobile DTV reception reliability, says Schadler

Dale Kelly wrote:

> SPX Communication Technology director of Advanced Antenna Systems Development
> John Schadler says circular and elliptical polarized DTV antennas are
> important tools in delivering a mobile DTV signal viewers can count on. *
>
http://broadcastengineering.com/news/circular-ellliptical-antenna-polarization-042111/
>
> *The benefits of Circular /elliptical polarization are well know and became
> standard practice about 60 years ago for FM radio broadcasters to enable
> reliable reception in moving vehicles.
>
> C.P was also used to improve reception of fixed analog TV receivers in many
> difficult reception conditions and is also utilized at a number of the DTV
> installations, particularly those constructed by Pappas telecasting.
>
> Our first C.P. television installation was a high powered fully circular
> antenna at WHNS-TV CH. 21, in North/South Carolina (about 1983). This 200
> KW transmitter is at a high mountain top installation near Brevard N.C.
> and resulted in the very best UHF reception in my experience, which is
> extensive. Within days of signing this station on the air we received a
> call from Georgia Public TVs Director of engineering asking; "what are
> y'all doing up there? I'm over a hundred and thirty miles away from your
> site and have perfect reception from a standard UHF antenna which is
> indoors on the floor. He was so impressed he visited the site to see this
> minor miracle in person.

Cool.

My take is, the reason that circular or elliptical polarization is also helpful for those with horizontal receive antennas is because it restores some of the signal that is lost with reflections and scatter. A horizontally polarized transmitted signal might not remain horizontally polarized, as it reflects off non-horizontal surfaces. So a horizontally polarized receive antenna would see a loss of signal strength, more than just that caused by distance from the transmitter.

A similarly reflected or scattered CP signal, instead, if the reflection didn't cause a lot of attenuation too, would look to a horizontally polarized receive antenna like a full strength signal.

The only issue is power. Does the FCC allow power to be increased if the transmit antenna is circularly polarized, compared to just horizontal or just vertical polarization? If not, then going to CP (especially) would possibly hurt some of the receivers out there. If no power increase is allowed, elliptical would be less of a potential liability for horizontally polarized receive antennas.

Bert



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