Relative Field Polar Plots on FCC website?? - AVS Forum
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post #1 of 7 Old 12-02-2002, 12:17 PM - Thread Starter
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Was looking at some of the summary info. for the Philly digital stations on the FCC website and ran across the "Relative Field Polar Plots" for several individual stations. I'm assuming that these show broadcast field strength as a function of distance and direction from the transmitter.....correct me if I'm wrong.

Attahed is the plot for WPHL-DT WB Philly. Several questions about this plot....

1. Labels on this plot are pretty scarce. The rings as you travel outward from the center represent distance...is that right? how are we supposed to know what the scale is? (ie. 10 miles per ring?)

2. I'm assuming the values in blue are signal strength of some type. what do these values represent? what would be their label?

3. Why is there not one of these plots for every station listed on the FCC website. There are no plots for KYW-CBS or WPVI-ABC in philly!!! Does someone actually go out and take measuremtns to create this plot, or is it projected/theoretical??


thanks in advance
LL
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post #2 of 7 Old 12-02-2002, 12:43 PM
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I may be wrong but I thought that this was a plot showing the charecteristics of the antenna they are using, I am sure someone on this forum can give a very good explanation of exactly what it means to us.

40° 42' 17" N 89° 36' 57" W
If a station is broadcasting and no-one can receive them, then are they broadcasting?
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post #3 of 7 Old 12-02-2002, 02:25 PM
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Quote:
Originally posted by dynamohum1
I may be wrong but I thought that this was a plot showing the charecteristics of the antenna they are using.
I'm quite sure you are correct. It's a plot of the transmitting antenna's expected radiation pattern, it doesn't show coverage area. Plots are not supplied for non-directional antennas which should have a circular radiation pattern.

Free signal strength/coverage map predictions for a specific receiving location can be found by clicking on the yellow banner at below link.(note, info is pulled from FCC engineering database at this site as well, but data on my local stations which are running at lower power/etc. with a STA doesn't seem to be available)

http://www.ardman.net

Jeff
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post #4 of 7 Old 12-02-2002, 03:05 PM
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Nitewatchman is correct, this is a plot of the antenna's radiation pattern.

The blue numbers indicate the field strength relative to the direction where the pattern contacts the outer ring, labeled 1.000. That is the direction that determines the stations ERP or effective radiated power.

To determine the power radiated in any other direction, multiply the blue number in that direction times the stations ERP.

For this antenna, if the ERP is 1 Megawatt, the power at 50 degrees and 290 degrees would be 474 Kilowatts.

PS. Oops! I forgot, voltage and power, see the post below for the correct formula.
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post #5 of 7 Old 12-02-2002, 03:28 PM
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Actually, to determine ERP in a given direction the formula is:
MAX ERP * relative field squared.
So if the relative field at a particular azimuth is .6 and the MAX ERP for the station is 1MW, the ERP that azimuth is:

(1,000,000W) * (.6*.6)= 360,000W
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post #6 of 7 Old 12-02-2002, 06:16 PM
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I stand corrected.
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post #7 of 7 Old 12-02-2002, 07:57 PM
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Spwace+VP,

Thanks much for the info. It's great to be able to figure these things out a little in order to get a bit better of an idea of how well my receiving antenna setup is working.

Jeff
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