RF Electronics Chapter 6: Oscillators Page 185
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 6.20 shows the spectra of all three Hartley oscillators. Comparing the spectrum of
the common collector (CC) oscillator with figure 6.11 shows that the Hartley oscillator
has a similar output, a lower second harmonic, but higher high frequency harmonics than
the Colpitts oscillator. This is to be expected, since Colpitts resonator with a ground
placed at the capacitor tapping point is like a low pass filter and the Hartley resonator
with the inductor tapping point is like a high pass filter. The Colpitts resonator will thus
attenuate harmonics more than the Hartley resonator. The common emitter (CE and CET)
oscillators have an 8 dB lower output voltage and a similar level of harmonic components.
Figure 6.21. Output waveforms of Hartley oscillators.
Figure 6.21 shows the waveforms from the 3 different Hartley oscillators. The output
voltage of the common emitter oscillators is smaller than that of the common collector
oscillator. Higher power oscillators should have a lower phase noise as is demonstrated
by this graph.
Figure 6.22. Phase Noise of Hartley oscillators.
The component values of the three Hartley oscillators of figures 6.17 to 6.19 have been
tuned to obtain a low phase noise. Figure 6.22 shows the resulting phase noise from the
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