Harmonic Analysis: Six-Segment Downhole Acoustic Waveguide - Measurement While Drilling Signal Analysis, Optimization and Design - page 83

2.6 Additional Engineering Conclusions
In Figures 2.10f,g,h, the frequency range is increased to 1,000 Hz. Two
results in this unfolding drama are surprising. First, the maximum transmission
efficiency increases to about 2.6, which is desirable. But even more important is
the number of good frequencies (strong signals) and their close proximity to bad
frequencies (weak signals). In a frequency-shift-keying (FSK) scheme, one
need not alternate between good frequencies and zero Hertz (that is, complete
siren stoppage, which imposes unreasonable system power demands associated
with siren rotor inertia). Alternating, say, between 50 and 60 Hz would increase
data rate (since more time is available for frequency cycling) while simplifying
mechanical design. From Figure 2.10h, there is no shortage of red peaks.
Figure 2.10f . Drillpipe p/'p to 200 Hz.
Figure 2.10g . Drillpipe p/'p to 300 Hz.