Sec.  15.231   Periodic operation in the band 40.66–40.70 MHz and above 70 MHz.

   (a) The provisions of this section are restricted to periodic operation
   within  the  band 40.66–40.70 MHz and above 70 MHz. Except as shown in
   paragraph (e) of this section, the intentional radiator is restricted to the
   transmission of a control signal such as those used with alarm systems, door
   openers, remote switches, etc. Continuous transmissions, voice, video and
   the radio control of toys are not permitted. Data is permitted to be sent
   with a control signal. The following conditions shall be met to comply with
   the provisions for this periodic operation:

   (1)  A  manually  operated transmitter shall employ a switch that will
   automatically deactivate the transmitter within not more than 5 seconds of
   being released.

   (2) A transmitter activated automatically shall cease transmission within 5
   seconds after activation.

   (3)  Periodic transmissions at regular predetermined intervals are not
   permitted. However, polling or supervision transmissions, including data, to
   determine  system integrity of transmitters used in security or safety
   applications are allowed if the total duration of transmissions does not
   exceed more than two seconds per hour for each transmitter. There is no
   limit  on  the  number of individual transmissions, provided the total
   transmission time does not exceed two seconds per hour.

   (4) Intentional radiators which are employed for radio control purposes
   during  emergencies involving fire, security, and safety of life, when
   activated to signal an alarm, may operate during the pendency of the alarm
   condition

   (5) Transmission of set-up information for security systems may exceed the
   transmission  duration  limits in paragraphs (a)(1) and (a)(2) of this
   section, provided such transmissions are under the control of a professional
   installer and do not exceed ten seconds after a manually operated switch is
   released  or  a  transmitter  is  activated automatically. Such set-up
   information may include data.

   (b)  In  addition  to the provisions of  Sec. 15.205, the field strength of
   emissions from intentional radiators operated under this section shall not
   exceed the following:
   Fundamental frequency (MHz) Field strength of fundamental (microvolts/meter)
   Field strength of spurious emissions (microvolts/meter)
   40.66–40.70 2,250 225
   70–130 1,250 125
   130–174 ^11,250 to 3,750 ^1125 to 375
   174–260 3,750 375
   260–470 ^13,750 to 12,500 ^1375 to 1,250
   Above 470 12,500 1,250

   ^1Linear interpolations.

   (1) The above field strength limits are specified at a distance of 3 meters.
   The tighter limits apply at the band edges.

   (2) Intentional radiators operating under the provisions of this section
   shall  demonstrate compliance with the limits on the field strength of
   emissions, as shown in the above table, based on the average value of the
   measured emissions. As an alternative, compliance with the limits in the
   above table may be based on the use of measurement instrumentation with a
   CISPR quasi-peak detector. The specific method of measurement employed shall
   be specified in the application for equipment authorization. If average
   emission measurements are employed, the provisions in  Sec. 15.35 for averaging
   pulsed emissions and for limiting peak emissions apply. Further, compliance
   with the provisions of  Sec. 15.205 shall be demonstrated using the measurement
   instrumentation specified in that section.

   (3) The limits on the field strength of the spurious emissions in the above
   table are based on the fundamental frequency of the intentional radiator.
   Spurious emissions shall be attenuated to the average (or, alternatively,
   CISPR quasi-peak) limits shown in this table or to the general limits shown
   in  Sec. 15.209, whichever limit permits a higher field strength.

   (c) The bandwidth of the emission shall be no wider than 0.25% of the center
   frequency for devices operating above 70 MHz and below 900 MHz. For devices
   operating above 900 MHz, the emission shall be no wider than 0.5% of the
   center frequency. Bandwidth is determined at the points 20 dB down from the
   modulated carrier.

   (d) For devices operating within the frequency band 40.66–40.70 MHz, the
   bandwidth of the emission shall be confined within the band edges and the
   frequency tolerance of the carrier shall be  ±0.01%. This frequency tolerance
   shall  be maintained for a temperature variation of −20 degrees to +50
   degrees C at normal supply voltage, and for a variation in the primary
   supply voltage from 85% to 115% of the rated supply voltage at a temperature
   of 20 degrees C. For battery operated equipment, the equipment tests shall
   be performed using a new battery.

   (e) Intentional radiators may operate at a periodic rate exceeding that
   specified in paragraph (a) of this section and may be employed for any type
   of  operation, including operation prohibited in paragraph (a) of this
   section, provided the intentional radiator complies with the provisions of
   paragraphs (b) through (d) of this section, except the field strength table
   in paragraph (b) of this section is replaced by the following:
   Fundamental frequency (MHz) Field strength of fundamental (microvolts/meter)
   Field strength of spurious emission (microvolts/meter)
   40.66–40.70 1,000 100
   70–130 500 50
   130–174 500 to 1,500^1 50 to 150^1
   174–260 1,500 150
   260–470 1,500 to 5,000^1 150 to 500^1
   Above 470 5,000 500

   ^1Linear interpolations.

   In addition, devices operated under the provisions of this paragraph shall
   be provided with a means for automatically limiting operation so that the
   duration of each transmission shall not be greater than one second and the
   silent period between transmissions shall be at least 30 times the duration
   of the transmission but in no case less than 10 seconds.

   [ 54 FR 17714 , Apr. 25, 1989;  54 FR 32340 , Aug. 7, 1989, as amended at  68 FR 68546 , Dec. 9, 2003;  69 FR 71383 , Dec. 9, 2004]