In continuous wave (CW) radio transmission, also called radiotelegraphy or on-off keying and designated by the International Telecommunication Union as emission type A1A, information is transmitted by pulses of unmodulated radio carrier wave which spell out text messages in Morse code.
Since in a superheterodyne receiver the different frequencies of the different stations are all translated to the same intermediate frequency (IF) by the mixer, modern BFOs which beat with the IF can have a constant frequency.