TOWER REGISTRATION

"Using these techniques will help satisfy the FCC's new tower registration requirements."

Whether your state has come up for tower registration yet or not, here's a few tips that may be helpful. To properly register your tower, its location, height and elevation must be confirmed using accurate data outside that which is already on file with the FCC. You can use 7 1/2 minute topo maps or GPS to confirm the coordinates. As an example, see an actual map in a separate browser window, (full size, 617 x 804 x 256 grays, 263K).

Using Topographic maps: The FCC will want your coordinates to use NAD 27 datum. Reading off the 7 1/2 minute (1:24,000) topo map will give you NAD 27 coordinates. It's best not to accept where you think the tower is located. Get yourself a 100' tape and actually measure to the base of the tower from an identifiable location on the map, then determine the coordinates.
Remember that the map is divided up into nine 2.5 minute by 2.5 minute segments. Each segment is bounded by four tic marks. If you look closely at the map you will see these tic marks.

The map, compressed to show the 2.5 minute tic marks on the edges, and the intersection of those tics.
The transmitter site(not shown) lies within this box.

Make A Working Copy. Use a copier to copy, at full scale, the portion of the map where your tower base falls. Make sure that all four tic marks are shown on the copy. (If you are near one of the four corners of the topo, you will have three tic marks and a corner mark.) The portion of the map this includes should just about fill up an 8 1/2 by 11" page.

Box In Your Site. Connect the tic marks together with a fine line. Determine the coordinates at the lower right hand corner of the section that contains your tower. Then measure the vertical and horizontal distance from those known coordinates. I use a millimeter drafting scale for this purpose.

Get Total Distance. Measure the total distance between the horizontal top and bottom lines and between the vertical side lines [ X and Y ].

Calculate the Latitude Proportion. Create a proportion (or "ratio") between the vertical distance of the tower from the horizontal base segment line and the full vertical distance of the segment. latitude proportion = Y_₁ / Y

Calculate the Longitude Proportion. Create another proportion for the horizontal distance between the right hand vertical segment line (the coordinates of which are known) and the actual tower location and the full horizontal distance between the right hand and left hand vertical segment lines. longitude proportion = X_₁ / X

Calculate the Number of Latitude Seconds. Multiply the derived latitude proportion times 150, which is the number of latitude seconds in the 2.5 minute segment. latitude seconds = ( Y_₁ / Y ) * 150

Calculate the Number of Longitude Seconds. Multiply the derived longitude proportion times 150, which is the number of longitude seconds in the 2.5 minute segment. longitude seconds = ( X_₁ / X ) * 150

These calculations will give you the number of seconds your tower is located above (north) and to the left (west) of the known coordinates.

Calculate the Transmitter's coordinates. Add the number of latitude seconds to the known latitude coordinate and the number of longitude seconds to the known longitude coordinate. Remember: There are sixty seconds to a minute; convert if necessary.
Your final coordinates are reported in degrees, minutes and seconds.

"With most GPS receivers, getting to NAD 27 will require some conversion..."

Using GPS. The Commission expects you to use this technique accurately, although they have not set out any GPS specifications, other than the accuracy of your coordinates must be within 50 feet. Many people do not know that you can purchase a handheld GPS unit from your local Wal-Mart for about $200. The accuracy of these units and other inexpensive units will vary considerably. You can these units as a double check to confirm a known site. However, you should be aware that the results can be from 300 to 500 meters off. This translates to 984 to 1640 feet, or from 9 to 16 seconds.

There is a way that you can improve upon the accuracy of these Wal-Mart units by ordering a beacon receiver for about $800. The beacon receiver introduces a differential correcting signal that will improve the accuracy of your measurement to better than the nearest second.

A unit commonly used by surveyors is the Trimble Navigator. By using this unit and the provided software, you can place a local base station at a known marker. This unit can be used to feed correction readings to a computer. Later, the readings can be combined with those taken at the tower base, and the software will produce extremely accurate corrections. This technique will give you millimeter accuracy. If you are a university station, you may find that your geography department has recently acquired this equipment, and they may be very excited about making your project a class project.

Remember that you will need to report your coordinate to the FCC in NAD 27. With most GPS receivers, getting to NAD 27 will require some conversion, particularly with the less expensive equipment. There are inexpensive computer programs on the market that will convert between the datums.

Confirming Tower Height. Tower height can be confirmed by looking back at your "as built" plans. If you can't find them, use a surveyor's transit to read the height to the top of the beacon. You should be able to do this yourself with just a few instructions, or you can hire a surveyor. A good surveyor will charge between $500 and $1,000 to determine your coordinates, your tower's height and ground elevation.

Once you have confirmed your tower's coordinates by either method, you can get the base elevation from a topo map. Remember to use the correct elevation intervals between contours. This information is located immediate below the distance scale at the center bottom of each topo map. Elevations can also be derived through correlating high-quality GPS measurements and known markers elevations.

When do I have to report a change? If your tower's height or base elevation varies by a foot or more from the recorded data, or if your confirmed coordinates are more than a second off, you will need to file a 7460-1 form with the FAA.

The FCC will require a "no hazard" determination from the FAA before they will accept your tower registration. If you can not get the "no hazard" issue from the FAA before your registration is due, you will need to ask the FCC for an extension.

Once you get an FAA determination for the corrected coordinates, height or elevation and register your tower with the FCC, you will need to file a form 854.
(It's your responsibility to ascertain if you must register your tower, and do so before the deadline. An excellent reference is the FCC's Antenna Structure Registration site, described below -ed).

What if there is a large discrepancy in your actual coordinates? You may have to submit a new allocation study showing that your interference signal contours do not overlap the protected signal contours of another station on your co-channel and adjacent channels. If you can not show a lack of contour overlap and that which exists has not already been waived by the Commission, you will have to reduce your power until the overlap disappears.

Using these techniques will help satisfy the FCC's new tower registration requirements. It's better to apply these techniques now than sheepishly having to amend your coordinates, elevation or tower height at a later date.

"HOW TO REGISTER" FROM THE FCC:
The following is from the FCC Antenna Registration Web Site (http://www.fcc.gov/wtb/antstruc.html) and lists the FCC-recommended steps. This information was copied on 30 October, 1997, and you are advised to check the site for changes.

In order to register a proposed antenna structure, or an altered antenna structure whose overall height has increased, the owner must:

Determine the location and height of the antenna structure;

Notify the FAA using FAA Form 7460-1;

Obtain a final determination of "no hazard" from the FAA concerning the antenna structure; and,

File FCC Form 854 and attach a copy of the most recent FAA determination of "no hazard" for the structure (no attachment needed if filing electronically).

When registering an existing antenna structure that has previously been studied by the FAA, the owner must:

Determine the location and height of the antenna structure. There is no requirement to re-survey the structure, but the applicant may do so if it is unsure of the validity of the site data originally provided to the FAA and FCC. (The FAA considers the structure to be "altered" and require a new FAA study if the actual site data differs from that of the previously studied site by more than one second in latitude, one second in longitude, or more than one foot (increase) in height. Altered antenna structures must follow the procedure outlined above.)

File FCC Form 854 and attach a copy of the most recent FAA determination (if available), or alternatively providing as much information as possible about the current FAA study for the antenna structure (no attachment necessary if filing electronically). Please note that the FCC does not retain copies of original FAA "determinations."

NOTE: In cases where structures were studied by the FAA many years ago, we realize that the owner may not have retained a copy of the FAA "determination." Therefore, a copy of the most recent FAA "determination" may not be necessary to register an existing structure. However, you must provide as much information as possible on FCC Form 854 concerning the structure's FAA Study Number, the FAA office notified, the date of FAA notification, and the previously assigned FCC Painting/Lighting Paragraphs (FCC Forms 715/715A). In most cases, this information will help the FCC verify that the structure was previously cleared by the FAA. If the site data does not appear in the FCC's current database of "cleared" structures, however, the FCC may require the owner to seek a new FAA "determination" prior to registration.

OBTAINING FCC FORM 854

To order 888-CALLFCC, or 800-418 FORM
Fax on Demand 202-418-0177 (you must call from your FAX's telephone handset)
On line, in both interactive version, and as a downloadable PDF file: www.fcc.gov/formpage.html
For help with locating your FAA study number, call the FCC Support Services Branch: 717-338-2560

FURTHER READING:

Antenna Structure Registration This excellent page is the on-line version of the FCC's Wireless Telecommunications Bureau Fact Sheet #15, "Antenna Structure Registration" and contains information about registering antenna structures with the Federal Communications Commission (FCC). Also downloadable in WordPerfect format as Fact Sheet #15

Global Positioning System Overview Peter H. Dana's excellent page that describes GPS in detail, how it works, and links to further GPS information.

Doug Vernier is the Director of Broadcasting Services at the University of Northern Iowa, a Broadcast Engineering Consultant, and President of V-Soft Communications (http://www.v-soft.com).
He can be reached at dvernier@v-soft.com

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