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Discussion Starter · #1 ·
Not exactly HDTV, but it is OTA. Simple question, simple answer:


Since virtually every TV antenna I've seen since I was a child (except for rabbit ears) has its elements arranged horizontally, implying that virtually all transmitter towers antennas have horizontal polarization - is this correct?


The reason I ask is that I just received the Silver Sensor UHF antenna I ordered (now if my STB would ever arrive), and its instructions show that you can mount the elements either horizontally or vertically, depending on which method your favorite stations use. Since it's manufactured in the UK, I'm assuming that both polarizations are in use over there.


I'm an electrical engineer, but it's been almost 20 years since I had any antenna theory (probably a single chapter). Anyone care to shed some light? What are the advantages of each polarization method? I'm assuming that horizontal polarization allows better signal gain per unit of transmit power, but what in instances would vertical be better? Highly dense, multi-story urban city dwellings (like NY, Chicago, etc.)?


Just don't tell BU I asked. This has absolutely nothing to do with COFDM vs. 8VSB!


[This message has been edited by jonlgauthier (edited 04-05-2001).]
 

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Neither polorization has more gain that the other. The main differences are that most noise is vertically polorized, so you can substantially reduce noise by using horizontal. The main uses for vertical (mainly FM broadcast stations which use dual polarity) is that most mobile receivers have vertically polorized antennas. Some TV stations may also use dual polorization. You would have to ask the station engineer.


Since bouncing off an object (building/mountain/etc) can cause a skew in the polarity, you may find in an urban setting, that one polarity works better than the other, irregardless of the transmitters polarity.



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DTV is horizontally polarized only, unlike analog which typically does have

a portion of the power directed to the vertical component..


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Bob Davis, DOE

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DTV antennas are not necessarily H-pol only. Many of the DTV stations already on-air, including KDVR-DT, have some V-pol. Check out the license data on the FCC website.
 

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Discussion Starter · #6 ·
Thanx for the responses, guys! I feel smarter already!
 

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Circular polarization????????

That is a new one on me.

Analog TV was mainly horizontal, then some verticle was added.

Polarization is basically matching the wave patterns to get the best signal to noise ratio.

Circular polarization is mainly used in display to get high contrast ratio.


Am I outdated, and is there really TV circular polarization?
 

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Okay, I stand corrected.

But, I did not clarify my statement.

Are the major broadcasters transmitting in circular polarization ? , not that it did not exist.

As I reviewed that site, it appears that only horizontal and/or verticle polarization are being used for broadcasts.

To maximize signal reception, you would want an antenna to match the polarization, and over 99% of the antennas are not circular.

Let us not get off on technicalities, but reality. Can you tell me what broadcast stations are transmitting in what polarizations? And are they VHF and/or UHF?
 

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Quote:
Originally posted by jonlgauthier:
...I just received the Silver Sensor UHF antenna I ordered (now if my STB would ever arrive), and its instructions show that you can mount the elements either horizontally or vertically, depending on which method your favorite stations use.
Got my Silver Sensor a few months ago, and found the orientation made a significant difference in multipath-riddled Manhattan. At an indoor mid-town location I couldn't pick up WNBC-DT from the distant World Trade towers in southern Manhattan with the typical orientation. But by pointing the tip of the S.S. 90 degrees from the WTC, with the plane of the elements vertical rather than horizontal, I easily picked up NBC (through numerous layers of shielded walls). Not sure if this relates to signal polarization or just exposing more antenna surface area to the broadcast antenna. -- John


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[This message has been edited by John Mason (edited 04-07-2001).]
 

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Bottom line, I do not believe any broadcast HDTV station will transmit circular polarization. If this was indeed true, than Channel Master would have big advertisments for this antenna.


So I believe that the majority of TV antenna is horizontal polarization, that would be the prime transmission. As stated earlier, there are more noise and multipath with verticle than horizontal, so this would logically be the method of choice.


I can not believe that general TV VHF broadcasters would transmit circular polarization. I can not see the technical justification as well with the ROI?


I do see verticle for FM and VHF so cars and such will have better reception.


The reason for my question on polarizatrion, is mainly in the UHF area.

CBS is mounting an antenna for HDTV in South Florida.

The pictures seem to show that it has verticle ports which would tend to lean to verticle polarization. Most UHF antenna is horizontal, so I wonder if both types of polarizations will be used.


House roof antenna's are usually horizontal polarization. Most indoor antenna's are verticle.

Just to be better informed, are there any home circular polarized antenna to receive major broadcast TV stations out there? And if so, what are they?
 

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Quote:
Originally posted by George33027:
Just to be better informed, are there any home circular polarized antenna to receive major broadcast TV stations out there? And if so, what are they?
Yes. DirecTV & EchoStar (they use left and right circular polarization) http://www.avsforum.com/ubb/smile.gif http://www.avsforum.com/ubb/biggrin.gif .


FWIW department, Most C-Band, some Ku-Band satellite use H or V polarization.


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Quote:
Originally posted by George33027:
Bottom line, I do not believe any broadcast HDTV station will transmit circular polarization. If this was indeed true, than Channel Master would have big advertisments for this antenna.


So I believe that the majority of TV antenna is horizontal polarization, that would be the prime transmission. As stated earlier, there are more noise and multipath with verticle than horizontal, so this would logically be the method of choice.


I can not believe that general TV VHF broadcasters would transmit circular polarization. I can not see the technical justification as well with the ROI?


I do see verticle for FM and VHF so cars and such will have better reception.


The reason for my question on polarizatrion, is mainly in the UHF area.

CBS is mounting an antenna for HDTV in South Florida.

The pictures seem to show that it has verticle ports which would tend to lean to verticle polarization. Most UHF antenna is horizontal, so I wonder if both types of polarizations will be used.


House roof antenna's are usually horizontal polarization. Most indoor antenna's are verticle.

Just to be better informed, are there any home circular polarized antenna to receive major broadcast TV stations out there? And if so, what are they?
The main advantage of circular polarization is that it reduces multipath since reflections have reversed chirality (e.g., the reflection of a CW CP signal is CCW). In theory, too, it can allow higher transmission levels without causing interference, although in practice the horizontal and vertical components become rather scrambled so I'm not sure how much of a practical advantage this represents. Also, someone did a study recently which indicated that multipath notches in the frequency response of digital signals occur in different places in the vertical and horizontal components of an ATSC signal.
 
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