Sec. 80.259  Technical requirements for radiotelegraph auto alarm 
          receiver.

    (a) For type acceptance the auto alarm in the absence of 
interference must be capable of being operated by four consecutive 
dashes whose length may vary from 6.0 to 3.5 seconds and the intervening 
spaces vary between 1.5 seconds to 10 milliseconds. These types of auto 
alarms must not respond to dashes longer than 6.31 seconds or shorter 
than 3.33 seconds nor to intervening spaces longer than 1.58 seconds or 
shorter than 5 milliseconds except as follows:
    (1) Non-digital types employing resistance-capacitance timing, type 
approved before October 1, 1969, and placed in service on or before 
January 1, 1985, must not respond to dashes longer than 7.40 seconds or 
shorter than 2.80 seconds, nor to space intervals longer than 1.80 
seconds or shorter than 5 milliseconds.
    (2) Digital types employing a stable clock as the basic timing 
device, type approved before May 1, 1968, and placed in service on or 
before December 1, 1975, may accept dashes whose lower limits extends 
down to 3.0 seconds.
    (b) The auto alarm must operate with a signal of 100 microvolts RMS 
at 500 kHz applied to an artificial antenna consisting of a 20 
microhenry inductance, a 500 picofarad capacitor, and a 5 ohm resistor 
connected in series in the absence of any interference and without 
manual adjustment. It must be capable of operation under these 
conditions on the following classes of emission:
    (1) A1B;
    (2) A2B with a carrier modulated at any modulation percentage from 
30 through 100 percent with any modulation frequency from 300 through 
1350 Hertz; and
    (3) H2B with a carrier keyed and emitted at any power level from 3 
through 6 decibels below peak envelope power, with any modulation 
frequency from 300 through 1350 Hertz.
    (c) The auto alarm must operate with signal levels up to 1 volt 
under normal operating conditions.
    (d) The auto alarm warning device must not be activated by 
atmospherics or by any signal from the antenna other than the alarm 
signal.
    (e) The auto alarms must respond to the alarm signal through non-
continuous interference caused by atmospherics and powerful signals 
other than the alarm signal. In the presence of atmospherics or 
interfering signals, the auto alarm must automatically adjust itself 
within a reasonable time to the condition in which it can most readily 
distinguish the alarm signal.
    (f) The auto alarm must respond without adjustment and with 
practically uniform sensitivity to signals over a band extending no less 
than 4 kHz on each side of the 500 kHz radiotelegraph frequency and with 
a minimum attenuation of:

5 dB at 495.0 kHz and 505.0 kHz
40 dB at 487.0 kHz and 513.0 kHz
80 dB at 475.0 kHz and 525.0 kHz

    (g) When the auto alarm is activated it must sound continuously a 
warning in the radiotelegraph operating room, in the radio operator's 
cabin, and on the bridge.
    (h) The auto alarm must include a 500 kHz signal generator and a 
keying device which automatically disconnects the auto alarm from the 
antenna when an alarm signal of 100 microvolts is applied to test the 
auto alarm.