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

  • From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Sat, 23 Apr 2011 17:54:54 -0700

Mark is correct of course. At the time of our WHNS construction I believe that 
he was in engineering management at Comark, the RF Company who supplied the 200 
KW transmitter. 

Fortunately the WHNS operation required only a 180 degree cardioid antenna 
pattern to cover the markets population thus requiring a relatively affordable 
power level.



C.P is a very expensive proposition for High powered UHF facilities. A station 
using a 360 degree antenna could easily require a 400 KW transmitter for full 
C.P. at full UHF power. Such an operation results in a VERY expensive 
transmitter facility with equally expensive utility bills and maintenance costs.



Many current DTV stations operate at relatively high UHF power levels and will 
face a very significant capital investment to produce the C.P signal (even 
elliptically) required to support mobile operations, as is suggested by 
Advanced Antenna systems.



However, the current VHF DTV stations, which operate at very miniscule 
authorized power levels, will require but a small investment to produce a C.P. 
signal and which would likely pass an ROI test.

Dale


From: Mark Aitken 
Sent: Friday, April 22, 2011 4:18 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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