Morse code has silent periods between its symbol elements (dots and dashes), letters, words, and sentences.
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.
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.
[4] 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.
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.
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.
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.
Subsequently, the two stations can then use the fluid and efficient Morse code conversational QSK protocols outlined in the following paragraphs.
Typically, without the protection and isolation provided by T/R switches, the receiver AFE would be overwhelmed or destroyed by the normal transmitter power levels which are in the +50 dBm or more range.
Consequently, radiotelegraph operators cannot hear interruptions from remote receiving stations during normal signal transmission periods when the full transmitter power is applied to the antenna.
Adding fast robust T/R switching externally to a transmitter/receiver combination (transceiver) will not necessarily result in good QSK operation.
Adding such fast switching externally to a transceiver may create transients within receiver circuitry that makes signal copy: very noisy at best, and difficult, or impossible at worst.
Many receivers have automatic gain control (AGC) circuits with time constants that take many milliseconds to recover their sensitivity and volume level after a strong transient signal is presented to their antenna input port.
Morse code operators aspiring to the convenience and conversational fluency of Morse code QSK operation who plan to add external QSK T/R switches to their existing or planned radio transceiver setups should ensure that their receiver AGC circuitry has recovery times commensurate with the T/R switching transients to be expected and that the AGC circuits can operate quickly in the sub-millisecond range without creating noisy pops and static at the receiver audio output (speaker or headphones).
For these reasons, generally most SDR radios will not have the capability to operate QSK at the higher speed Morse code rates.
Expensive high end radio transceiver equipment that has been designed and manufactured with integrated QSK capability will generally meet such fast AGC recovery time requirements.
Full break-in hardware capability requires fast, robust, high power, analog, radio frequency (RF) transmit/receive (T/R) switches or RF switches capable of operating in sub-millisecond response times over long periods of continuous operation while handling the high radio frequency power of the transmitter.
[5] 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.
At 20 word per minute code speed this means that QSK T/R switching times must be in the range of 1 to ½ millisecond or below.
[7][8] An alternative approach uses power relays for QSK operation by adding a few milliseconds of delay in the keying line.
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.
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.