[1000mp] Key clicks

[John L Merrill]

This is from the expanded Mk5 Field ARRL review. The graphs, which I cannot
show you in plain text mode show cw sidebands down 60db 3khz either side of
center freq. The 756 pro did a little better at 70db down.

CW Keying Waveforms and Sidebands
Test Description: The purpose of the CW Keying Waveform Test is to determine
the shape of the transmitter's RF output envelope in the CW mode. If the
transmitter under test has several CW modes, (VOX, QSK) these are also
tested. A picture of the oscilloscope screen is taken of the results. The
first and second dits are shown in all modes.
If the rise or fall times become too short, the transmitter may generate key
clicks. Most click-free transmitters have rise and fall times between 1 and
5 ms. However, key clicks are most often generated by sudden transactions in
the keying envelope (e.g., "square corners"), so a short rise or fall time
is not a guarantee of clicks.
The absolute values of the on delay and off delay are not critical, but it
is important that they be approximately the same so that CW weighting will
not be affected. Some transmitters used in the VOX mode exhibit a first dit
that is shorter than subsequent dits. Other transmitters can show
significant shortening of all dits when used in the QSK mode. The latter
will cause keying to sound choppy.
This test also measures the sidebands generated by the transceiver on high
speed CW. This is an indication of the degree to which a transmitter may
exhibit 'key clicks'. The transmitter is keyed at 60-wpm by an external
circuit. The sidebands are measured on the spectrum analyzer using a
resolution bandwidth of 300 Hz, and a long sweep time (30 seconds) so the
worst-case spectrum is captured.
Key Test Conditions:
The transmitter is operated at room temperature at rated output power into a
50-ohm resistive load. The power supply voltage is nominal.
Figure Notes (Figures on next page):
Figure 1 shows the keying waveform from the oscilloscope with the
transceiver in QSK. Semi-QSK is not shown, but the waveform is virtually
identical. The top trace is the voltage on the keying line of the
transceiver (the external keying circuit uses an open-collector transistor
in its output). A low voltage on this line indicates the transmitter "key
down" condition. The second trace is the actual transmitter output. The
horizontal axis is 10 ms/division, and the keying rate is 60 wpm. The first
and second dits are shown, and some traces also show the beginning of the
third dit
Figure 2 shows the keying sidebands from the spectrum analyzer for a
continuous string of dits at 60 wpm, with the analyzer set to a 300 Hz
resolution bandwidth (for easier comparison with previously published keying
sidebands plots)
Figure 3 shows the keying sidebands from the spectrum analyzer for a
continuous string of dits at 60 wpm, with the analyzer set to a 10 Hz
resolution bandwidth, but with the data adjusted for an equivalent 500 Hz
bandwidth, and the middle 500 Hz removed from the plot. The analyzer was set
to peak hold mode, and 10 sweeps were taken.
ARRL Laboratory Expanded Test-Result Report Model: Yaesu FT-1000MP Mark V
Field, serial: 2C010120 Copyright 2002.