§  80.213   Modulation requirements.

   (a) Transmitters must meet the following modulation requirements:

   (1) When double sideband emission is used the peak modulation must be
   maintained between 75 and 100 percent;

   (2) When phase or frequency modulation is used in the 156–162 MHz band
   the peak modulation must be maintained between 75 and 100 percent. A
   frequency deviation of ±5 kHz is defined as 100 percent peak
   modulation; and

   (3) In single sideband operation the upper sideband must be
   transmitted. Single sideband transmitters must automatically limit the
   peak envelope power to their authorized operating power and meet the
   requirements in § 80.207(c).

   (b) Radiotelephone transmitters using A3E, F3E and G3E emission must
   have a modulation limiter to prevent any modulation over 100 percent.
   This requirement does not apply to survival craft transmitters, to
   transmitters that do not require a license or to transmitters whose
   output power does not exceed 3 watts.

   (c) Coast station transmitters operated in the 72.0–73.0 MHz and
   75.4–76.0 MHz bands must be equipped with an audio low-pass filter. The
   filter must be installed between the modulation limiter and the
   modulated radio frequency stage. At frequencies between 3 kHz and 15
   kHz it must have an attenuation greater than at 1 kHz by at least
   40log[10](f/3) dB where “f” is the frequency in kilohertz. At
   frequencies above 15 kHz the attenuation must be at least 28 dB greater
   than at 1 kHz.

   (d) Ship and coast station transmitters operating in the 156–162 MHz
   and 216–220 bands must be capable of proper operation with a frequency
   deviation that does not exceed ±5 kHz when using any emission
   authorized by § 80.207.

   (e) Coast station transmitters operated in the 156–162 MHz band must be
   equipped with an audio low-pass filter. The filter must be installed
   between the modulation limiter and the modulated radio frequency stage.
   At frequencies between 3 kHz and 20 kHz it must have an attenuation
   greater than at 1 kHz by at least 60log[10](f/3) dB where “f” is the
   audio frequency in kilohertz. At frequencies above 20 kHz the
   attenuation must be at least 50 dB greater than at 1 kHz.

   (f) Radiodetermination ship stations operating on 154.585 MHz, 159.480
   MHz, 160.725 MHz, 160.785 MHz, 454.000 MHz and 459.000 MHz must employ
   a duty cycle with a maximum transmission period of 60 seconds followed
   by a minimum quiescent period four times the duration of the
   transmission period.

   (g) Radar stations operating in the bands above 2.4 GHz may use any
   type of modulation consistent with the bandwidth requirements in
   § 80.209(b).

   (h) Radar transponder coast stations using the 2900–3100 MHz or
   9300–9500 MHz band must operate in a variable frequency mode and
   respond on their operating frequencies with a maximum error equivalent
   to 100 meters. Additionally, their response must be encoded with a
   Morse character starting with a dash. The duration of a Morse dot is
   defined as equal to the width of a space and 1/3 of the width of a
   Morse dash. The duration of the response code must not exceed 50
   microseconds. The sensitivity of the stations must be adjustable so
   that received signals below −10 dBm at the antenna will not activate
   the transponder. Antenna polarization must be horizontal when operating
   in the 9300–9500 MHz band and either horizontal or both horizontal and
   vertical when operating in the 2900–3100 MHz band. Racons using
   frequency agile transmitting techniques must include circuitry designed
   to reduce interference caused by triggering from radar antenna
   sidelobes.

   (i) Variable frequency ship station transponders operating in the
   2900–3100 MHz or 9300–9500 MHz band that are not used for search and
   rescue purposes must meet the following requirements:

   (1) Non-selectable transponders must have the following
   characteristics:

   (i) They must respond on all their frequencies with a maximum range
   error equivalent to 100 meters;

   (ii) They must use a Morse encoding of “PS” (dot-dash-dash-dot,
   dot-dot-dot), meaning “You should not come any closer”. The width of a
   Morse dot is defined as equal to the width of a space and1/3of the
   width of a Morse dash;

   (iii) When they employ swept frequency techniques they must not
   transmit on any frequency for more than 10 seconds in any 120 second
   period;

   (iv) Any range offset of their response must occur during their pause
   on the fixed frequency;

   (v) The duration of the response code must not exceed 50 microseconds;

   (vi) The sensitivity of the stations must be adjustable so that
   received signals below −10 dBm at the antenna input will not activate
   the transponder;

   (vii) Antenna polarization must be horizontal when operating in the
   9300–9500 MHz band and either horizontal or both horizontal and
   vertical when operating in the 2900–3100 MHz band.

   (viii) Transponders using frequency agile techniques must include
   circuitry designed to reduce interference caused by triggering from
   radar antenna sidelobes.

   (2) Selectable transponders must be authorized under part 5 of the
   Commission's rules until standards for their use are developed.

   (j) The transmitted signals of search and rescue transponders must
   cause to appear on a radar display a series of at least 20 equally
   spaced dots.

   (k) The modulation requirements for EPIRB's are contained in subpart V.

   [ 51 FR 31213 , Sept. 2, 1986, as amended at  52 FR 7418 , Mar. 11, 1987;
    52 FR 28825 , Aug. 4, 1987;  54 FR 40058 , Sept. 29, 1989;  57 FR 43407 ,
   Sept. 21, 1992;  65 FR 77824 , Dec. 13, 2000;  68 FR 46965 , Aug. 7, 2003;
    69 FR 64673 , Nov. 8, 2004]