Sec. 15.247  Operation within the bands 902-928 MHz, 2400-2483.5 MHz, 
          and 5725-5850 MHz.

    (a) Operation under the provisions of this section is limited to 
frequency hopping and direct sequence spread spectrum intentional 
radiators that comply with the following provisions:
    (1) Frequency hopping systems shall have hopping channel carrier 
frequencies separated by a minimum of 25 kHz or the 20 dB bandwidth of 
the hopping channel, whichever is greater. The system shall hop to 
channel frequencies that are selected at the system hopping rate from a 
pseudorandomly ordered list of hopping frequencies. Each frequency must 
be used equally on the average by each transmitter. The system receivers 
shall have input bandwidths that match the hopping channel bandwidths of 
their corresponding transmitters and shall shift frequencies in 
synchronization with the transmitted signals.
    (i) For frequency hopping systems operating in the 902-928 MHz band: 
if the 20 dB bandwidth of the hopping channel is less than 250 kHz, the 
system shall use at least 50 hopping frequencies and the average time of 
occupancy on any frequency shall not be greater than 0.4 seconds within 
a 20 second period; if the 20 dB bandwidth of the hopping channel is 250 
kHz or greater, the system shall use at least 25 hopping frequencies and 
the average time of occupancy on any frequency shall not be greater than 
0.4 seconds within a 10 second period. The maximum allowed 20 dB 
bandwidth of the hopping channel is 500 kHz.
    (ii) Frequency hopping systems operating in the 2400-2483.5 MHz and 
5725-5850 MHz bands shall use at least 75 hopping frequencies. The 
maximum 20 dB bandwidth of the hopping channel is 1 MHz. The average 
time of occupancy on any frequency shall not be greater than 0.4 seconds 
within a 30 second period.
    (2) For direct sequence systems, the minimum 6 dB bandwidth shall be 
at least 500 kHz.
    (b) The maximum peak output power of the intentional radiator shall 
not exceed the following:
    (1) For frequency hopping systems operating in the 2400-2483.5 MHz 
or 5725-5850 MHz band and for all direct sequence systems: 1 watt.
    (2) For frequency hopping systems operating in the 902-928 MHz band: 
1 watt for systems employing at least 50 hopping channels; and, 0.25 
watts for systems employing less than 50 hopping channels, but at least 
25 hopping channels, as permitted under paragraph (a)(1)(i) of this 
section.
    (3) Except as shown in paragraphs (b)(3) (i), (ii) and (iii) of this 
section, if transmitting antennas of directional gain greater than 6 dBi 
are used the

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peak output power from the intentional radiator shall be reduced below 
the stated values in paragraphs (b)(1) or (b)(2) of this section, as 
appropriate, by the amount in dB that the directional gain of the 
antenna exceeds 6 dBi.
    (i) Systems operating in the 2400-2483.5 MHz band that are used 
exclusively for fixed, point-to-point operations may employ transmitting 
antennas with directional gain greater than 6 dBi provided the maximum 
peak output power of the intentional radiator is reduced by 1 dB for 
every 3 dB that the directional gain of the antenna exceeds 6 dBi.
    (ii) Systems operating in the 5725-5850 MHz band that are used 
exclusively for fixed, point-to-point operations may employ transmitting 
antennas with directional gain greater than 6 dBi without any 
corresponding reduction in transmitter peak output power.
    (iii) Fixed, point-to-point operation, as used in paragraphs 
(b)(3)(i) and (b)(3)(ii) of this section, excludes the use of point-to-
multipoint systems, omnidirectional applications, and multiple co-
located intentional radiators transmitting the same information. The 
operator of the spread spectrum intentional radiator or, if the 
equipment is professionally installed, the installer is responsible for 
ensuring that the system is used exclusively for fixed, point-to-point 
operations. The instruction manual furnished with the intentional 
radiator shall contain language in the installation instructions 
informing the operator and the installer of this responsibility.
    (4) Systems operating under the provisions of this section shall be 
operated in a manner that ensures that the public is not exposed to 
radio frequency energy levels in excess of the Commission's guidelines. 
See Sec. 1.1307(b)(1) of this chapter.
    (c) In any 100 kHz bandwidth outside the frequency band in which the 
spread spectrum intentional radiator is operating, the radio frequency 
power that is produced by the intentional radiator shall be at least 20 
dB below that in the 100 kHz bandwidth within the band that contains the 
highest level of the desired power, based on either an RF conducted or a 
radiated measurement. Attenuation below the general limits specified in 
Sec. 15.209(a) is not required. In addition, radiated emissions which 
fall in the restricted bands, as defined in Sec. 15.205(a), must also 
comply with the radiated emission limits specified in Sec. 15.209(a) 
(see Sec. 15.205(c)).
    (d) For direct sequence systems, the peak power spectral density 
conducted from the intentional radiator to the antenna shall not be 
greater than 8 dBm in any 3 kHz band during any time interval of 
continuous transmission.
    (e) The processing gain of a direct sequence system shall be at 
least 10 dB. The processing gain represents the improvement to the 
received signal-to-noise ratio, after filtering to the information 
bandwidth, from the spreading/despreading function. The processing gain 
may be determined using one of the following methods:
    (1) As measured at the demodulated output of the receiver: the ratio 
in dB of the signal-to-noise ratio with the system spreading code turned 
off to the signal-to-noise ratio with the system spreading code turned 
on.
    (2) As measured using the CW jamming margin method: a signal 
generator is stepped in 50 kHz increments across the passband of the 
system, recording at each point the generator level required to produce 
the recommended Bit Error Rate (BER). This level is the jammer level. 
The output power of the intentional radiator is measured at the same 
point. The jammer to signal ratio (J/S) is then calculated, discarding 
the worst 20% of the J/S data points. The lowest remaining J/S ratio is 
used to calculate the processing gain, as follows: Gp = (S/N) o + Mj + 
Lsys, where Gp = processing gain of the system, (S/N) o = signal to 
noise ratio required for the chosen BER, Mj = J/S ratio, and Lsys = 
system losses. Note that total losses in a system, including intentional 
radiator and receiver, should be assumed to be no more than 2 dB.
    (f) Hybrid systems that employ a combination of both direct sequence 
and frequency hopping modulation techniques shall achieve a processing 
gain of at least 17 dB from the combined techniques. The frequency 
hopping operation of the hybrid system,

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with the direct sequence operation turned off, shall have an average 
time of occupancy on any frequency not to exceed 0.4 seconds within a 
time period in seconds equal to the number of hopping frequencies 
employed multiplied by 0.4. The direct sequence operation of the hybrid 
system, with the frequency hopping operation turned off, shall comply 
with the power density requirements of paragraph (d) of this section.
    (g) Frequency hopping spread spectrum systems are not required to 
employ all available hopping channels during each transmission. However, 
the system, consisting of both the transmitter and the receiver, must be 
designed to comply with all of the regulations in this section should 
the transmitter be presented with a continuous data (or information) 
stream. In addition, a system employing short transmission bursts must 
comply with the definition of a frequency hopping system and must 
distribute its transmissions over the minimum number of hopping channels 
specified in this section.
    (h) The incorporation of intelligence within a frequency hopping 
spread spectrum system that permits the system to recognize other users 
within the spectrum band so that it individually and independently 
chooses and adapts its hopsets to avoid hopping on occupied channels is 
permitted. The coordination of frequency hopping systems in any other 
manner for the express purpose of avoiding the simultaneous occupancy of 
individual hopping frequencies by multiple transmitters is not 
permitted.

    Note: Spread spectrum systems are sharing these bands on a 
noninterference basis with systems supporting critical Government 
requirements that have been allocated the usage of these bands, 
secondary only to ISM equipment operated under the provisions of part 18 
of this chapter. Many of these Government systems are airborne 
radiolocation systems that emit a high EIRP which can cause interference 
to other users. Also, investigations of the effect of spread spectrum 
interference to U. S. Government operations in the 902-928 MHz band may 
require a future decrease in the power limits allowed for spread 
spectrum operation.

[ 54 FR 17714 , Apr. 25, 1989, as amended at  55 FR 28762 , July 13, 1990; 
 62 FR 26242 , May 13, 1997]