Elliptical polarization coming to some DTV stations in Canada

[ralph_sinclair]

I don't think anyone has mentioned this. Most of the CTV applications are on VHF-HI. Many of these applications are for a flash cut on the same channel. However, CTV will be replacing most of their VHF-HI transmit antennas with new elliptically polarized (70% H 30% V) models at a cost of around $400k per antenna.

CTV VHF stations using new elliptically polarized antenna:
Lethbridge
Saskatoon
Regina
Winnipeg
CKVR A Barrie (new antenna as they move from channel 3)
Charlottetown

CTV VHF stations re-using exisiting horizontally polarized antenna:
Kitchener
Saint John

Unknown (applications not yet published or I missed them):
Edmonton - seems to be elliptical based on FCC data tables
CFPL A London - seems to be elliptical based on FCC data tables
Toronto
Ottawa
Montreal (I thought I read about a new CTV VHF-hi antenna on the Mont-Royal candelabra)

Non-CTV stations licensed for elliptical polarization according to FCC:
Global Edmonton
Global Winnipeg (UHF 40)

I haven't noticed elliptical or circular polarization on anyone's UHF applications or on the monster 60kW CBC Regina application

(reusing the existing tx antenna).

All of the coverage maps and calculations and published ERP's are based on only the horizontal component, so we can think of the vertical component as a "bonus".

So, what does elliptical polarization mean? I assume it will help with mobile device reception. In short, with a vertically polarized walkie talkie, you want to stick the antenna straight up and down. With horizontally polarized yagi TV antenna, the elements lie flat. Can we expect these elliptically polarized signals to travel better over hilly terrain or in cities? Probably. Could the DIY folks on this site design special 70%H 30%V EP polarized VHF-Hi antennas? I expect so!

Here are some nearby US stations licensed for elliptical/circular polarization:
KCPQ Tacoma (E)
WJBK Detroit (C)
WDIV Detroit (C)
WKBD Detroit (E)
WCPO Cleveland (E)
WEWS Cleveland (E)
WQHS Cleveland (E)
WNYO Buffalo (E)
WNYB Jamestown (E)
WSYT Syracuse (E)

California, Florida, Denver, Houston, and NYC have many CP or EP licensed stations.

links:
http://www.astronwireless.com/topic-...larization.asp
http://www.tvtechnology.com/article/67946
http://www.tvtechnology.com/article/68820

[ota_canuck]

Some of the existing antenna designs on this forum are capable of both polarizations and/or are capable of being modified to do both. I know the Stealth Hawk has done well for an Australian member who needed both vert/horiz reception. It's possible that elliptical/circular polarization will eventually become the standard for all OTA broadcasters.

[JamesK]

based on FCC filings

Why would they be filing with the FCC? That's the U.S. regulator. We have Industry Canada.

[ralph_sinclair]

JamesK,

As I'm sure you are aware, IC and the FCC need to co-ordinate data for regions within 350km of the border. I found these links in my research:

http://www.rabbitears.info/oddsanden...ization&type=C
http://www.rabbitears.info/oddsanden...ization&type=E

and they perfectly correlated with published CTV applications. So I think it's safe to say these stations will use elliptical polarization as well.

Perhaps Stampeder can extend his already excellent IC extract pages to include polarization type. Although to me the best indicator is the published applications from the broadcasters.

I think it is interesting to note that CTV will NOT be using CP or EP on brand new UHF antennas such as Halifax and Moncton - it seems to be a VHF-only thing for CTV.

[stampeder]

The purpose of using elliptical polarization is to be future-ready for Mobile ATSC services due to the needs of such mobile devices to be able to receive well regardless of the orientation of the device. As to why only CTV's VHF TX antennas are doing it, that sounds like a corporate decision to me.

No worries for consumers who watch standard ATSC DTV because all of our present OTA gear will work just fine with elliptical polarized signals.

[JamesK]

IC and the FCC need to co-ordinate data for regions within 350km of the border.

Quite so, which is why Canadian broadcasters file with I.C. I.C. then deals with the FCC as necessary.

BTW, how far is Edmonton from the U.S. border?

[Trip]

Originally Posted by ralph_sinclair

JamesK,

As I'm sure you are aware, IC and the FCC need to co-ordinate data for regions within 350km of the border. I found these links in my research:

http://www.rabbitears.info/oddsanden...ization&type=C
http://www.rabbitears.info/oddsanden...ization&type=E

I wonder whose site that is.

and they perfectly correlated with published CTV applications. So I think it's safe to say these stations will use elliptical polarization as well.

They should. I hand-updated as many of the entries as I could to reflect what the IC database contains. If you spot any errors, please let me know so I can fix them. I may have overlooked some.

Perhaps Stampeder can extend his already excellent IC extract pages to include polarization type. Although to me the best indicator is the published applications from the broadcasters.

Unless I overlooked it (definitely possible), I didn't see a field in the IC database that states the polarization. I was looking for it when I went to use the information to update RabbitEars.

I think it is interesting to note that CTV will NOT be using CP or EP on brand new UHF antennas such as Halifax and Moncton - it seems to be a VHF-only thing for CTV.

Originally Posted by stampeder

The purpose of using elliptical polarization is to be future-ready for Mobile ATSC services due to the needs of such mobile devices to be able to receive well regardless of the orientation of the device. As to why only CTV's VHF TX antennas are doing it, that sounds like a corporate decision to me.

Actually, there's significant evidence that upper-VHF reception is significantly aided by adding vertical power, particularly for indoor antennas that may not be perfectly horizontal.

Originally Posted by JamesK

Quite so, which is why Canadian broadcasters file with I.C. I.C. then deals with the FCC as necessary.

BTW, how far is Edmonton from the U.S. border?

Far enough that it doesn't require FCC coordination. I had to add those to RabbitEars by hand.

- Trip

[stampeder]

Section 1.2.2 in the following Agilent PDF document (posted elsewhere today by ProjectSHO89) has a good technical explanation of wave propagation vis-a-vis elliptical polarization:

http://www.home.agilent.com/agilent/...LENT_EDITORIAL

[99gecko]

With horizontal polarization, the rf burn hazard was relatively low unless you happened to be the poor technician who was convinced to go work on a high powered antenna, fully juiced.

Sooooo I'm curious,.... since there is a vertical component to an elliptical radiation pattern, can anyone speculate on what the environmental hazard might be for the suckers working on the top floor of perhaps First Canada Place, home to a few of Toronto's broadcast antennas, if any of them were to change to elliptical polarization?

Or would the much lower power of DTV transmitters simply make it a low hazard, much like FM radio (mixed polarity) since the tx power is lower than traditional analog television?

BTW, I just chose that building as it was the first one I could think of that has TV stations broadcasting off of it.

Or have I got it all wrong?

[Dave Loudin]

Remember that the field radiated straight down is much less than the peak value out towards the horizon.

[GeorgeMx]

Originally Posted by 99gecko

With horizontal polarization, the rf burn hazard was relatively low unless you happened to be the poor technician who was convinced to go work on a high powered antenna, fully juiced.

Sooooo I'm curious,.... since there is a vertical component to an elliptical radiation pattern, can anyone speculate on what the environmental hazard might be for the suckers working on the top floor of perhaps First Canada Place, home to a few of Toronto's broadcast antennas, if any of them were to change to elliptical polarization?

Or would the much lower power of DTV transmitters simply make it a low hazard, much like FM radio (mixed polarity) since the tx power is lower than traditional analog television?

BTW, I just chose that building as it was the first one I could think of that has TV stations broadcasting off of it.

Or have I got it all wrong?

I think you are confusing vertical polarization with vertical radiation pattern. Polarization in radio waves is the same phenomenon as polarization in light. Wearing polarized sunglasses does not change what you see, it just changes the intensity and eliminates certain kinds of glare. If it worked the way you assumed radio energy worked with vertical polarization then you would be able to see your feet and forehead at the same time

The vertical antenna radiation pattern is a different thing. If the antenna was a ball then energy would be radiated in all directions more or less equally. The antennas used for television broadcasting squeeze the pattern from the top and bottom to concentrate the energy toward the horizon or slightly below it (electrical downtilt). The electromagnetic energy has traditionally been transmitted with horizontal polarization but this has nothing to do with the antenna's vertical radiation pattern. Elliptical polarization simply means that the electromagnetic field will have a vertical polarization component as well as a horizontal polarization component. If a broadcaster wants to convert from horizontal to elliptical or circular polarization while keeping the same power in the horizontal polarization component, additional transmitter power is required. Full circular polarization requires twice the amount of power as horizontal only.

As far as the effect on humans is concerned, the only thing that matters is the total amount of energy, not the polarization.

[GeorgeMx]

Originally Posted by stampeder

The purpose of using elliptical polarization is to be future-ready for Mobile ATSC services due to the needs of such mobile devices to be able to receive well regardless of the orientation of the device. As to why only CTV's VHF TX antennas are doing it, that sounds like a corporate decision to me.

No worries for consumers who watch standard ATSC DTV because all of our present OTA gear will work just fine with elliptical polarized signals.

I think there is another consideration which is rotation of polarization when signals are reflected by buildings and terrain. If the horizontal component is twisted toward the vertical by a reflection then the vertical component will be twisted toward the horizontal by the same amount. VHF hi has problems in urban areas so adding a vertical component will assist with reception in difficult locations particularly for users of indoor antennas (rabbit ears).

[old sparks]

Exactly! In fact, a left-hand CP signal will become right-hand CP when it reflects off a surface, but for a linear-polarized antenna, the signal strength will remain the same.

There is a 3 dB 'hit' when receiving a CP signal with a linear antenna, less for an elliptically-polarized signal.

[ota_canuck]

Originally Posted by old sparks

Exactly! In fact, a left-hand CP signal will become right-hand CP when it reflects off a surface, but for a linear-polarized antenna, the signal strength will remain the same.

There is a 3 dB 'hit' when receiving a CP signal with a linear antenna, less for an elliptically-polarized signal.

So, what effect will this have on reflected multipath issues?

Found this:
http://www.antenna-theory.com/basics/polarization.php

[holl_ands]

Antennas with Circular Polarization, including the controversial ON-AIR tests,
can be found here:
http://www.digitalhome.ca/forum/show....php?p=1080294
http://www.digitalhome.ca/forum/show....php?p=1205374