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Four Tone Input and Output Response of
Elecraft K3 for Various Levels of RF Clipping
The oscilloscope images below are for a four-tone signal
generated by an HP8904A function generator. The four tones, of equal amplitude,
are:
- 1000 Hz
- 1025 Hz
- 1050 Hz
- 1075 Hz
The upper trace (black) shows the signal generator output.
The lower trace (blue) shows the K3's "monitor" output, and includes the effects
of RF clipping. I've also enabled measurement mode for both traces with their
peak-to-peak and RMS values calculated and displayed.
The time offset between the two images represents the time
required by the K3's DSP to digitize the input waveform, to perform the speech
processing and then to convert it back to an output audio signal. In
fact, the time delay amounts to 6 horizontal divisions. (I measured the
processing time as 31.0 ms—click here
to see the details.)
As the clipping level increases, note the change in the
low level signals during the interval before and after the stronger burst. Also
note the change in Channel 2's peak-to-peak and RMS signal level, and in
particular the ratio of RMS to peak.
By clipping level 15, it's apparent that the rounded input
waveform burst is flattened to a more rectangular waveform. At clipping level
25, the main and secondary bursts are almost identical in amplitude. At clipping
level 35, almost 100% of the amplitude variation in the test waveform is
removed, and at clipping level 40, the output waveform looks almost like a
continuous amplitude signal.
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