QSK operation (full break-in)

Full break-in or QSK operation,[1][2][3] is a hardware supported Morse code communications channel turn over communications protocol. Full break-in is a so-called duplexing protocol, that 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.

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.[4]

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 durations 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 (citation needed) as described in the following paragraph.

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.

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 has QSK capability. Subsequently, the two stations can then utilize 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.

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.

Upon hearing the break-in signal between the dots and dashes being sent, the interrupted station stops sending immediately and either: (a) just pauses momentarily or, (b) sends a single letter K prosign (▄▄▄▄▄▄▄▄▄▄▄▄) meaning "go ahead" and pauses momentarily, thus turning over the channel to the interrupter, and subsequently listens for the other station during the momentary pause. Highly skilled fluent telegraphists seldom bother to send the K prosign when interrupted instead simply letting the interrupter take over the channel during the pause.

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.

These simple full break-in channel turn over protocols literally mimic the conversational style in which people interrupt each other mid-syllable during normal voice conversations. Full break-in QSK T/R switch hardware together with use of the simple QSK protocols enables a fast, efficient, fluid conversational style of Morse code communication.

As an example illustrating switching speeds or timing requirements consider that when sending Morse code at a 20 word per minute rate the typical dot signal duration is a mere 50 milliseconds. To enable good quality QSK operation the switching hardware must switch the radio antenna from receiver to transmitter in much less than one tenth of the dot duration. At 20 word per minute code speed this means that QSK T/R switching times must be in the range of 1 to 1/2 millisecond or below. Even smaller sub-millisecond times are required with higher speed Morse code transmissions.

The dotting rate of Morse code is the reciprocal of the dot duration, e.g. at twenty words per minute based upon the standard word PARIS with a dot duration of 50 milliseconds, the dotting rate is twenty times per second (20 = 1.0/0.05). The dotting rate is even faster for higher speed Morse code. For long time reliability QSK T/R switches must be robust enough to open and close at least at a dotting rate of twenty times per second or even higher over thousands of hours of operation.

T/R switches must operate reliably at high dotting rates over many thousands of hours enabling the reception of extremely low level signals between dots and dashes while handling very high radio transmitter power levels of hundreds to thousands of Watts. Such robust high power analog radio frequency high speed switches are not inexpensive.

Examples of radio frequency analog hardware switch or RF switch technologies are: high voltage vacuum relays[6] or high power semiconductor PIN diode switches. In recent times, as PIN diode power handling capabilities have been improved by the semiconductor industry, PIN diodes have largely supplanted vacuum relays in the QSK switch function because the absence of moving parts in PIN diode semiconductor devices results in: higher speeds, higher reliability and longer lifetimes. [7][8] An alternative approach uses power relays for QSK operation by adding a few milliseconds of delay in the keying line. [9]

Switching hardware technologies that can handle the radio frequency currents of high power transmitters and also switch quietly at these high Morse code rates over long periods of time are difficult to design and quite expensive to manufacture. Mechanical switches or relays are most problematic and least reliable and must be protected from arcs (sparking) usually by operating in a vacuum enclosure with elaborate timing circuitry. Not all radio transceiver equipment provides the costly high speed analog transmit/receive (T/R) radio frequency switching hardware support necessary for QSK full break-in operation. Generally full break-in is available only on more expensive radio transceivers. Radiotelegraphers who aspire to the fluency of Morse code QSK operation must ensure that their radio equipment includes the hardware capability for radio frequency antenna switching that operates rapidly enough to allow listening between signals at the appropriate Morse code sending speeds with appropriate lifetimes and reliability.