In CW Morse code operations, QSK or full break-in operation describes an operating mode in which the transmitting station can detect signals from other stations between the elements (dots and dashes) or letters of the Morse transmission. This allows other stations to interrupt the transmitting station between individual coding elements, and such allows for a conversational style of communication. "QSK" is one of the Q-code signals established for radiotelegraph operators in the first decade of the 1900s. The three letter code "QSK" literally means "I can hear you between my signals; you may break in on my transmission." Although Morse code is no longer used for commercial or professional purposes, it continues to be used in amateur radio. In QSK or full break-in operation the silent periods between the Morse code dits and dahs enable operators to listen between their transmitted signals for signals from the other operator, thus enabling a conversational style of communication. This is especially useful in high-speed telegraphy.
Signals, silent periods and symbols Morse code has silent periods between its symbol elements (dots and dashes), letters, words, and sentences. These silent periods provide the sending operator with opportunities to listen for interruptions from receiving stations. Whereas in usual CW operation the sending carrier wave is always on, and only gated to the antenna, in QSK operation the antenna is switched to receiver status on the off-time between dits and dahs, and then switched right back. This fast switching between sending and receiving on the transceiver sending the current message segment lets the sending side of the conversation hear that the receiving side has switched to transmitting, in between the off-times of Morse code. The intermixed signal is normally too garbled for either station to decode the other. But when the QSK sender does hear the other station's sound filling in the normally silent gaps between the sender's own sent code elements, that informs the sender that the other station wants to break in, and the sender then has the option to politely stop and let the other operator back into the conversation early, before the sender has finished his / her current message segment.
QSK transmit/receive (T/R) switch operation QSK operation is a technical challenge: It requires very fast T/R RF switches at the high power and voltage side of the radio transceiver. Such switches must be controlled automatically by the telegraph key, and as such they must be rapid enough to be perceptually undetectable by the telegraph operator. In QSK operation, the T/R switches must be capable of automatically and rapidly switching the radio antenna or antennas between the transmitter and receiver during the short (dot duration) silent periods between Morse code signals, sometimes hundreds or even thousands of times per minute, for years on end. As such, the T/R switches used in QSK operation generally have the most stringent timing, reliability, and power handling specifications of all, and are quite expensive. Typically switching of this kind is taken on by vacuum reed switches, maybe aided by high voltage PIN diodes, and sometimes augmented by various circuit improvements that passively take the load off the active elements.
Full break-in or QSK operation Full break-in or QSK operation, is a hardware supported Morse code communications channel turn over communications protocol. So, full break-in is also a duplexing protocol, which facilitates a style of two-way Morse code communications on traditional half-duplex radiotelegraph channels that closely simulates full-duplex channel operations similar to the way normal human voice communications proceeds. It is not just a technology, but also a communications protocol and culture revolving around said technology. With full break-in operation, the receiving operator can interrupt a sending operator in mid-character, similar to the way in which normal human voice conversations allow mid-syllable interruption of speakers by listeners. This makes it possible to creatively break the normal Morse or other radiotelegraphy protocols, and as such, in QSK-operation, many informal idioms appear which are not in use in more codified forms of telegraphy. For instance, to take turn in conversation, a held note of indefinite length and often varying by discussion/discussee, can be used. This is only possible because the other participant can hear a held note between his keying his own tone. Or as another break from convention, not only do high speed telegraphers often sign off with two non-spaced dits. Many of those whom go with HST and QSK sign off with rather elaborate combinations of dits, dahs, bad spacing, and a "click" here and there. As such, QSK, in its communicational style, also leads to lots of conversational style, which cannot be codified for real.
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