V & H antenna radiated power

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kcbooboo
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V & H antenna radiated power

Post by kcbooboo » Wed Sep 27, 2017 1:18 pm

Let's say a translator is licensed for 200 watts ERP into a directional yagi antenna with 6dB gain and this antenna is horizontally oriented, so TPO is about 50 watts (assume no loss in the coax). If they connect a second 6dB gain yagi through an appropriate power splitter and orient it vertically and point it in the same direction, does this changed their licensed ERP at all? In other words, is the ERP measured in one orientation only or is it the sum of all radiated ERPs? Obviously the TPO would be increased to support the radiation from the second antenna and the splitter loss.

Would an FIM typically measure just the horizontal field intensity or must it be oriented to also read the vertical signal?

Obviously a vertically oriented antenna will provide a different coverage area than a horizontal one, and would be better for vehicular (vertical) reception vs home/office (horizontal) reception.

Thanks.

Bob M.

W2XJ
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Re: V & H antenna radiated power

Post by W2XJ » Wed Sep 27, 2017 2:26 pm

A few points. First, ERP is generally calculated in the horizontal plane but the FCC lists horizontal and vertical separately. Vertical ERP can not exceed horizontal. Remember if you put a splitter in the transmission line you will require twice the TPO for the same ERP. You will not really have circular polarization unless the elements are in quadrature. Also, be careful about directional pattern as that yagi has a different pattern in the vertical plane.

Your assumption that vertical is better for mobile reception is an old wives tale. Back when vehicales had vertical whips it wasn’t true but now where very few vehicles had vertical whips the conversation is all but irrelevant.

I think a better solution is slant polarization. More and more translators are being built that way. Just take the existing yagi and put it on a 45 degree slant. Increase the TPO to 100 watts and file a modification with the FCC. They will consider the ERP to be half horizontal and half vertical.

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Deep Thought
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Re: V & H antenna radiated power

Post by Deep Thought » Wed Sep 27, 2017 7:24 pm

ERP is calculated in the horizontal plane regardless of polarization, at 0°from horizontal. That's often a point of confusion. The vertical plane is usually an entirely different pattern depending on the number of bays, etc.

FM stations are licensed for x ERP horizonal and/or y ERP vertical polarization. Being licensed for H-pol only or V-pol only doesn't preclude adding the other polarization without a construction permit unless there was an allocation reason for the configuration (such as TV channel 6 protection). The coverage area is the same with either.

In your example the power divider would cut the input power to the existing antenna in half. Adding the second antenna with cross polarization does not increase the gain as it would if they were in the same polarization, so you'd have to double the TPO for the same ERP. This additional radiated power density is why CP or H/V antennas do have better building penetration regardless of what is said elsewhere. How would it not? "Slant polarization" doesn't really get you that.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

kcbooboo
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Re: V & H antenna radiated power

Post by kcbooboo » Thu Sep 28, 2017 6:41 am

Thanks for the replies. Sorry, I have to admit to being an old wife, or at least knowing one (and yes, I have stayed at a Holiday Inn more than once).

Bob M.

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