Electronic Filing
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MB E-Filing Site
These FCC/MB forms MUST be electronically filed:
FCC Forms 301, 301-CA, 302-CA, 302-FM, 302-DTV, 302-TV, 303-S, 314,
315, 316, 318, 319, 323, 323-E, 337, 340, 346, 347, 349,
350, 381
EEO Forms 395-A and 395-B have been suspended by
Commission Order FCC 01-34.
CDBS Users Guide or call (202)-418-2662
CDBS System Status
Call Sign Reservations & Authorizations
for broadcast
station call signs
Antenna Structure Registration via ULS
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Easy, one-stop access to all online U.S. Federal Government resources
www.USA.gov
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AM Ground System Correction Factors
for Nondirectional AM Stations
AM antenna systems consist in part of an underground ground
system in addition to the vertical
antenna. A standard ground system consists of 120 copper
radials, each 1/4 wavelength in
length, buried in the earth surrounding the central tower (at 3
degree intervals). These radials look like the spokes of a
bicycle wheel, but they are not connected at the outer ends.
Each radial is electrically connected to the other radials at the
bottom of the base insulator beneath the vertical tower section.
However, some nondirectional AM stations operate with fewer than
120 radials, or with radials truncated in some or all directions. The tables below
provide correction factors applied by the staff to
Figure 8, 47 CFR 73.190, to compute the theoretical
efficiency of a simple vertical nondirectional antenna under
these conditions. The effective
field for the nonstandard antenna, in mV/m, is REDUCED by the
amounts specified below. For example, a ground system consisting of 90 radials
with an average length of 0.192 wavelengths would result in a cumulative
correction factor of (-9.7 mV/m @ 1 km) + (-16.1 mV/m @ 1 km) = (-25.8 mV/m @ 1km).
Thus, the effective field strength
value determined from Figure 8 would be reduced by 25.8.
These correction factors may not be applied to
towers in an AM directional array.
Radials Less Than 1/4 Wavelength in
Length
| Average lengths of
radials in wavelengths |
Correction factor
(mV/m @ 1
km) |
|---|
| 0.2401 or greater | 0 |
| 0.2301 to 0.2400 | -3.2 |
| 0.2201 to 0.2300 | -6.4 |
| 0.2101 to 0.2200 | -9.7 |
| 0.2001 to 0.2100 | -12.9 |
| 0.1901 to 0.2000 | -16.1 |
| 0.1801 to 0.1900 | -19.3 |
| 0.1701 to 0.1800 | -22.5 |
| 0.1601 to 0.1700 | -25.7 |
| 0.1501 to 0.1600 | -29.0 |
AM Ground Systems with Less Than 120
Radials
| Number of
Radials |
Correction factor
(mV/m @ 1
km) |
|---|
| 110 | -3.2 |
| 100 | -6.4 |
| 90 |
-9.7 |
Notes:
- For simple vertical antennae over salt water, use Figure 8
directly. Do NOT make the above adjustments.
- Use the minimum permissible radiation figures shown below for
antennas with roof top ground systems,
T-shaped and L-shaped antennas, and for simple vertical systems having
ground systems too
short to fall within the range of corrections noted above, as follows:
| Class A (except Alaskan) | 362 mV/m @ 1 km |
| Class B, D, and Alaskan A | 282 mV/m
@ 1 km |
| Class C | 241 mV/m @ 1
km |
47 CFR Section 73.182(m)
Use these minimums if the corrected Figure 8 values result in
effective fields below these permissible minimum values. Please note that a
nondirectional proof of performance
may be required in cases where the antenna system efficiency is
questionable.
Top-loaded, sectionalized, or other types of antennas must be
considered on a case-by-case basis.
This page is located at http://www.fcc.gov/fcc-bin/audio/amgnd.html.
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