47 CFR § 80.98 - Radiotelegraph testing procedures.
Stations authorized to use telegraphy may conduct tests on any assigned frequency. Emissions must not cause harmful interference. When radiation is necessary the radiotelegraph testing procedure described in this paragraph must be followed:
(a) The operator must not interfere with transmissions in progress.
(b) The operator must transmit “IE” (two dots, space, one dot) on the test frequency as a warning that test emissions are about to be made.
(c) If any station transmits “AS” (wait), testing must be suspended. When transmission of “IE” is resumed and no response is heard, the test may proceed.
(d) Test signals composed of a series of “VVV” having a duration of not more than ten seconds, followed by the call sign of the testing station will be transmitted. The call sign must be sent clearly at a speed of approximately 10 words per minute. This test transmission must not be repeated until a period of at least one minute has elapsed.