Elecraft K2 Keying Modification Instructions - Manual

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Elecraft K2 Keying Modification Instructions
Rev. A, Feb. 3, 2004
Introduction
The modifications described here significantly reduce the K2's CW keying bandwidth, while not making
the keying too soft. This change is recommended for all K2s, but is especially important for stations
operating at high power, which are more likely to interfere with nearby stations. NOTE: You must
update your K2 firmware to revision 2.04P or later when you make these changes (see next page).
Technical Details
Recent analysis has shown that the keying bandwidth of many transceivers is excessive. A consensus has
emerged that a sigmoidal (S-shaped) envelope, rather than a classic R-C exponential envelope, is ideal.
The K2 can be modified accordingly. As shown below, the new keying waveform has longer rise and fall
times, and the abrupt falling edge is eliminated.
Most of the changes are in the key shaping circuitry (U10A, Control board). The R-C shaping network is
reconfigured as a two-pole low-pass filter. In addition, a capacitor is added from the VPWR line (U8 pin
2) to ground to reduce the slew rate of the power-control DAC signal. Finally, a high-performance PIN
diode replaces the original D36 on the RF board to prevent control signal leak-through during keying.