47 CFR § 80.229 - Special requirements for automatic link establishment (ALE).
Brief signalling for the purposes of measuring the quality of a radio channel and thereafter establishing communication shall be permitted within the 2 MHz-30 MHz band. Public coast stations providing high seas service are authorized by rule to use such signalling under the following conditions:
(a) The transmitter power shall not exceed 100 W ERP;
(b) Transmissions must sweep linearly in frequency at a rate of at least 60 kHz per second, occupying any 3 kHz bandwidth for less than 50 milliseconds;
(c) The transmitter shall scan the band no more than four times per hour;
(d) Transmissions within 6 kHz of the following protected frequencies and frequency bands must not exceed 10 µW peak ERP:
(1) Protected frequencies (kHz)
(2) Protected bands (kHz)
(e) The instantaneous signal, which refers to the peak power that would be measured with the frequency sweep stopped, along with spurious emissions generated from the sweeping signal, must be attenuated below the peak carrier power (in watts) as follows:
(1) On any frequency more than 5 Hz from the instantaneous carrier frequency, at least 3 dB;
(2) On any frequency more than 250 Hz from the instantaneous carrier frequency, at least 40 dB; and
(3) On any frequency more than 7.5 kHz from the instantaneous carrier frequency, at least 43 + 10log10 (peak power in watts) db.