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Bill93

Towers In Fcc Asr Data Base

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I was looking up some antennas found in the NGS data base using the FCC Antenna Structure Registration data base and find small discrepancies in the latitude and longitude.

 

How accurate are the FCC coordinates? Were they just scaled off a topo or were they surveyed? If I find a 30 foot difference is that evidence that a new foundation and tower have been put in, or does it take 300 foot difference to be good evidence?

 

The dates in the ASR data don't look like they are reliable for actual construction dates, as they seem to get re-registered to different owners.

 

What is the greatest reasonable lifetime for a tower? If there is one in the NGS data base from 1975 could it still be there? 1956? 1940?

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Excellent question, Bill. As I recall from filling out applications for towers, a survey was not required. My experience was in "pre-GPS" days. Since the coordinates are for helping aircraft avoid the structure, and given the speed airplanes travel, a few tenths of a degree probably won't make much difference.

 

Ditto for other uses of the coordinates, which include:

 

*Calculating the coverage area of the transmitter; especially in the broadcasting industry, and with cellular towers (where frequencies are re-used in nearby cells). In both industries, licenses are granted for a specific Statistical Metropolitian Area.

 

*Identifying the site in case of interference. (Recent case: A paging transmitter in Raleigh NC was putting a "spur" on the approach frequency for RDU.)

 

*Determing local sunset/sunrise. (Tower lights must be on during a specified period, and the license generally comes with a chart showing the hours when lighting is required for the tower.)

 

I have not had to submit or renew an application in several decades. The FCC web page probably contains the current requirements.

 

-Paul-

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I am pretty sure you are correct Paul. The coordinates must be more for navigation than for exact location. There is a 4 tower array near me that lists all four at the same coordinates. They string out about 400 feet though, so they would have different coordinates if they were precise.

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The positions for vast majority of the towers listed in the FCC data base are scaled from a topo map. About 10 years ago I had an opportunity to work with FCC to migrate their data from the old North American Datum of 1927 (NAD 27) to the North American Datum of 1983 (NAD 83). In reviewing their reporting proceedures I found that the form submitted by the tower owner/operator had spaces for degrees, minutes and whole seconds and absolutely no requirements for reporting the source of the position. NGS attempted to get FCC to do a database match so that the positions we have in the National Spatial Reference System would be matched by what FCC had. They weren't interested - too much effort. I'm not aware of any significant changes to their reporting requirements since then.

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I wonder if use of GPS (I don't know if they do) in aircraft for navigation would make the lack of accurate location information in the FCC database dangerous.

 

 

The scale on aero charts I've seen didn't leave much room for detail, and having things to the nearest ddmmss probably is adequate.

 

Any pilots who can comment? Let's hear from the data users!

 

-Paul-

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