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.
Semi break-in operation Semi break-in is a technique used by stations where slow (T/R) antenna switches are controlled indirectly by the telegraph key which lack the faster switching of full break-in stations. Semi break-in hardware T/R switches are not required to switch as fast or to have the same long term reliability as their more expensive full break-in counterparts. Instead of using the telegraph key to directly control antenna switching, semi break-in radio transceiver equipment typically uses the telegraph key to control T/R switches indirectly, but still automatically, by passing the telegraph key information (usually in the form of a keyed audio tone) through a radio transceiver's Voice-operated switch or VOX circuitry.
In this technique, the relatively slow acting VOX circuitry is used to control the T/R switches. Voice-operated switch (VOX) circuitry is designed to be normally activated by human voice audio picked up by the transceiver microphone during voice communications in order to effect antenna change over at a rate no faster than the typical human voice syllabic rate or slower. VOX circuitry usually has a front panel adjustable delay that can be used to control the length of time it takes for T/R switches to operate but generally the delay adjustment range is limited to that of human voice syllables and, although automatic, is generally not fast enough to act in the short periods between Morse code dots and dashes. Receiving stations thus cannot break-in or interrupt semi break-in or VOX controlled Morse code stations in mid-symbol or mid-word, during Morse code operation because the semi break-in sending station simply cannot hear in the short duration between the Morse code signals and words or code groups.
Receiving stations wishing to break-in on semi break-in stations must wait for the longer silent periods between the sending station's words or sentences before attempting to interrupt or break-in. At worst, receiving stations must wait until semi break-in stations explicitly turn over the channel to the receiving station by sending a break prosign. Unlike full break-in operation, semi break-in operation is not fast enough to provide a fluid Morse code conversational capability approximating that of normal human voice conversation.
Although not as fluid and efficient as full break-in, semi break-in or VOX controlled break-in is a better Morse code channel turn over technique than pure manual break-in operation as described in the following paragraph.
Manual break-in operation
Manual break-in is a technique used in a rudimentary Morse code radio station set up where antenna change over (T/R) switches are not controlled by the telegraph key. Instead antenna change over is accomplished manually by mechanical switches separate from the telegraph key on which the operator sends the Morse code. With such a simple manual turn over system there is no possibility of the sending operator listening between signals or symbols and therefore no possibility for the receiving operator to interrupt the sending operator. Instead the receiving operator must wait until a transmitting operator has indicated the end of transmission by means of a turn over prosign and has manually changed the antenna over from transmitter to receiver. Such manual break-in operation leads to a very slow and stilted style of Morse code conversations.
QSK protocols QSK operation comprises a hardware switch technology and protocol, wherein participating Morse code stations are equipped with very fast analog radio frequency T/R switches connecting the transmitter, receiver, and antenna. This fast analog hardware switching capability enables a receiving station to interrupt or break-in on a transmitting station in mid-symbol (mid-character), a process known as full break-in. The ability to hear between transmitted signals conferred by fast radio frequency hardware switching only requires Morse code operators to make use of simple communications protocols to manage the channel turn over process. The typical QSK protocol technique is quite simple to learn and to master.
Opening protocol Since not all Morse code radio stations are equipped for QSK operation, sending stations equipped for QSK operation will often open a Morse conversation by sending the three letter group QSK (e.g. the operator will assert QSK) during an initial (opening) Morse code transmission to alert receiving stations that the sending station has the ability to listen between signals and that the receiving station can interrupt, or break-in, on the sending station at will. Conversely a station may query another Morse code station's QSK capability by sending the QSK signal followed by a question mark. The query QSK? asks if the receiving station has full break-in capability. If a receiving station is equipped for QSK operation the receiving operator will respond to the query QSK? with the assertion QSK indicating that the station is operating with QSK enabled. Subsequently, the two stations can then use the fluid and efficient Morse code conversational QSK protocols outlined in the following paragraphs.
In practice, many skilled operators do not bother to open a conversation with the preliminary opening QSK assertion or QSK query protocols, instead merely attempting to interrupt a sending station by tapping their telegraph key while listening between the signals (dots and dashes) for what happens next. If the sending station pauses when interrupted each party automatically knows the other is using QSK operation and then the two stations immediately start using the following QSK interrupt and turn over protocol with no further ado.
Interrupt protocol Interruptions or break-ins are initiated by receiving stations momentarily depressing their telegraph key while the sending station is actively sending Morse code, thus generating a short interrupting signal which is heard by the sending station between its own signals. In practice usually only a single dot is required to initiate a break-in.
Turn over protocol Upon hearing the break-in signal between the dots and dashes being sent, the interrupted station stops sending immediately and (a) just pauses momentarily or, (b) optionally sends the end-of-message prosign (equiv. Morse "+", ) to indicate "I'm done", (c) sends a single letter prosign () meaning "go ahead" and pauses momentarily, either way turning over the channel to the interrupter, and subsequently listens for the other station during the momentary pause. Skilled telegraphists seldom bother to send the prosign when interrupted, instead simply letting the interrupter take over the channel during the pause.
Ongoing channel control protocol The interrupting station, recognizing the momentary sending pause by the sender, immediately begins sending its own information to the interrupted station. Meanwhile, the interrupting station continues listening between its own transmitted signals in case of interruption in the reverse direction by the original sender.