Sec. 21.113  Quiet zones.

    Quiet zones are those areas where it is necessary to restrict 
radiation so as to minimize possible impact on the operations of radio 
astronomy or other facilities that are highly sensitive to radio 
frequency interference. The areas involved and procedures required are 
as follows:
    (a) In order to minimize possible harmful interference at the 
National Radio Astronomy Observatory site located at Green Bank, 
Pocahontas County, West Virginia, and at the Naval Radio Research 
Observatory site at Sugar Grove, Pendleton County, West Virginia, any 
applicant for a station authorization other than mobile, temporary base, 
or temporary fixed seeking authorization for a new station or to modify 
an existing station in a manner which would change either the frequency, 
power, antenna height or directivity, or location of such a station 
within the area bounded by 39 deg.15' N. on the north, 78 deg.30' W. on 
the east, 37 deg.30' N. on the south, and 80 deg.30' W. on the west 
shall, at the time of filing such application with the Commission, 
simultaneously notify the Director, National Radio Astronomy 
Observatory, Post Office Box No. 2, Green Bank, West Virginia 24944, in 
writing, of the technical particulars of the proposed operation. Such 
notification shall include the geographical coordinates of the antenna, 
antenna height, antenna directivity (if any), proposed frequency, type 
of emission, and power. In addition, the applicant shall indicate in his 
application to the Commission the date notification was made to the 
Observatory. After receipt of such applications, the Commission will 
allow a period of twenty (20) days for comments or objections in 
response to the notifications indicated. If an objection to the proposed 
operation is received during the 20-day period from the National Radio 
Astronomy Observatory for itself or on behalf of the Naval Radio 
Research Observatory,

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the Commission will consider all aspects of the problem and take 
whatever action is deemed appropriate.
    (b) In order to minimize possible harmful interference at the Table 
Mountain Radio Receiving Zone of the Research Laboratories of the 
Department of Commerce located in Boulder County, Colorado, applicants 
for new or modified radio facilities in the vicinity of Boulder County, 
Colorado are advised to give due consideration prior to filing 
applications, to the need to protect the Table Mountain Radio Receiving 
Zone from harmful interference. To prevent degradation of this present 
ambient radio signal level at the site, the Department of Commerce seeks 
to ensure that the field strengths of any radiated signals (excluding 
reflected signals) received on this 728.4 hectare (1800 acre) site (in 
the vicinity of coordinates 40 deg. 07' 50' N Latitude, 105 deg. 15' 40' 
W Longitude) resulting from new assignments (other than mobile stations) 
or from the modification or relocation of existing facilities do not 
exceed the following values:

                                                                        
------------------------------------------------------------------------
                                                    Field     Power flux
                                                  strength   density \1\
                                                  (mV/m) in  (dbW/m2) in
                Frequency range                  authorized   authorized
                                                  bandwidth   bandwidth 
                                                 of service   of service
------------------------------------------------------------------------
Below 540 kHz..................................          10        -65.8
540 to 1600 kHz................................          20        -59.8
1.6 to 470 MHz.................................          10    \2\ -65.8
470 to 890 MHz.................................          30    \2\ -54.2
Above 890 MHz..................................           1   \2\ -85.8 
------------------------------------------------------------------------
\1\ Equivalent values of power flux density are calculated assuming free
  space characteristic impedance of 376.7=120 ohms.            
\2\ Space stations shall conform to the power flux density limits at the
  earth's surface specified in appropriate parts of the FCC rules, but  
  in no case should exceed the above levels in any 4 kHz band for all   
  angles of arrival.                                                    

    (1) Advance consultation is recommended particularly for those 
applicants who have no reliable data which indicates whether the field 
strength or power flux density figures in the above table would be 
exceeded by their proposed radio facilities (except mobile stations). In 
such instances, the following is a suggested guide for determining 
whether coordination is recommended:
    (i) All stations within 2.4. kilometers (1.5 miles);
    (ii) Stations within 4.8 kilometers (3 miles) with 50 watts or more 
average effective radiated power (ERP) in the primary plane of 
polarization in the azimuthal direction of the Table Mountain Radio 
Receiving Zone;
    (iii) Stations within 16.1 kilometers (10 miles) with 1 kW or more 
average ERP in the primary plane of polarization in the azimuthal 
direction of Table Mountain Receiving Zone;
    (iv) Stations within 80.5 kilometers (50 miles) with 25 kW or more 
average ERP in the primary plane of polarization in the azimuthal 
direction of Table Mountain Receiving Zone.
    (2) Applicants concerned are urged to communicate with the Radio 
Frequency Management Coordinator, Department of Commerce, Research 
Support Services, NOAA R/E5X2, Boulder Laboratories, Boulder, CO 80303; 
telephone (303) 497-6548, in advance of filling their applications with 
the Commission.
    (3) The Commission will not screen applications to determine whether 
advance consultation has taken place. However, applicants are advised 
that such consultation can avoid objections from the Department of 
Commerce or proceedings to modify any authorization which may be granted 
which, in fact, delivers a signal at the site in excess of the field 
strength specified herein.
    (c) Protection for Federal Communications Commission monitoring 
stations:
    (1) Applicants in the vicinity of an FCC monitoring station for a 
radio station authorization to operate new transmitting facilities or 
changed transmitting facilities which would increase the field strength 
produced over the monitoring station over that previously authorized are 
advised to give consideration, prior to filing applications, to the 
possible need to protect the FCC stations from harmful interference. 
Geographical coordinates of the facilities which require protection are 
listed in Sec. 0.121(c) of the Commission's Rules. Applications for 
stations (except mobile stations) which will produce on any frequency a 
direct wave fundamental field strength of greater than 10 mV/m in the 
authorized bandwidth of service (-65.8 dBW/m2 power flux 
density assuming a free space characteristic impedance of 120 ohms)

[[Page 47]]

at the referenced coordinates, may be examined to determine extent of 
possible interference. Depending on the theoretical field strength value 
and existing root-sum-square or other ambient radio field signal levels 
at the indicated coordinates, a clause protecting the monitoring station 
may be added to the station authorization.
    (2) In the event that calculated value of expected field exceeds 10 
mV/m (-65.8 dBW/m2) at the reference coordinates, or if there 
is any question whether field strength levels might exceed the threshold 
value, advance consultation with the FCC to discuss any protection 
necessary should be considered. Prospective applicants may communicate 
with: Chief, Compliance and Information Bureau, Federal Communications 
Commission, Washington, DC 20554, Telephone (202) 632-6980.
    (3) Advance consultation is suggested particularly for those 
applicants who have no reliable data which indicates whether the field 
strength or power flux density figure indicated would be exceeded by 
their proposed radio facilities (except mobile stations). In such 
instances, the following is a suggested guide for determining whether an 
applicant should coordinate:
    (i) All stations within 2.4 kilometers (1.5 statute miles);
    (ii) Stations within 4.8 kilometers (3 statute miles) with 50 watts 
or more average effective radiated power (ERP) in the primary plane of 
polarization in the azimuthal direction of the Monitoring Stations.
    (iii) Stations within 16.1 kilometers (10 miles) with 1 kW or more 
average ERP in the primary plane of polarization in the azimuthal 
direction of the Monitoring Station.
    (iv) Stations within 80.5 kilometers (50 miles) with 25 kW or more 
average ERP in the primary plane of polarization in the azimuthal 
direction of the Monitoring Station.
    (4) Advance coordination for stations operating above 1000 MHz is 
recommended only where the proposed station is in the vicinity of a 
monitoring station designated as a satellite monitoring facility in 
Sec. 0.121(c) of the Commission's Rules and also meets the criteria 
outlined in paragraphs (c) (2) and (3) of this section.
    (5) The Commission will not screen applications to determine whether 
advance consultation has taken place. However, applicants are advised 
that such consultation can avoid objections from the Federal 
Communications Commission or modification of any authorization which 
will cause harmful interference.
[ 44 FR 60534 , Oct. 19, 1979, as amended at  44 FR 77167 , Dec. 31, 1979; 
 50 FR 39001 , Sept. 26, 1985;  52 FR 37783 , Oct. 9, 1987;  58 FR 44894 , 
Aug. 25, 1993;  61 FR 8477 , Mar. 5, 1996]

Secs. 21.114-21.115  [Reserved]