All-Ears QSK Timing Generator

Published:2013/3/7 3:10:00 Author:Ecco | Keyword: All-Ears, QSK, Timing Generator | From:SeekIC

In the world of amateur (ham) radio morse code communications, QSK refers to a method of operation where the transmitter and receiver are alternately active when the key is down or up. QSK is also known as break-in keying. QSK operation allows the operator to hear what is happening on their frequency in the brief times between transmitting morse code dits and dahs. The conversation can be quickly interrupted by the other station, or by a third station. The sender also knows immediately if their signal is being interfered with. The design of a QSK-capable radio station is somewhat tricky. A QSK system has to quickly switch the antenna between the transmitter and receiver, key the transmitter, mute the receiver during transmission and disable the transmitter's oscillator during receiving. It is also desirable to change the receiver's AGC response time from fast to slow when not transmitting. By adding small delays at the beginning and ending of the dots and dashes, it is possible to generate signals with slightly longer and shorter lengths compared the original morse code. These modified signals sequence the entire system in order to eliminate transmitted chirps, T/R relay arcing and receiver clicking. Here's a typical sequence for sending one morse code dit , items in parentheses happen simultaneously: (key down, T/R relay to transmit, transmitter oscillator on, receiver mute), delay, transmitter output on for duration of dit, (key up, transmitter output off), delay, (T/R relay to receive, transmitter oscillator off, receiver unmute) Additionally, the receiver AGC slow/fast signal needs to go to fast at the beginning the the first key down event, and should switch to fast a few seconds after the last key up event. This circuit takes a TTL-level keying signal and produces three TTL-level output signals, and inverted versions of the three signals. This combination of outputs is useful for driving a variety of control circuits that can interface to the transmitter and receiver. The timing generator also generates the necessary signals for automatic non-QSK transmit/receive switching.



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