Advanced System Summary and Modern MWD Developments - Measurement While Drilling Signal Analysis, Optimization and Design - page 275

Figure 10.1. A typical resistivity-at-bit (or, “RAB”) tool.
An unweighted mud is taken with a typical sound speed of 3,500 ft/sec and
we considered frequencies up to 100 Hz. The results indicate that a 60 Hz
carrier with the pulser located 0-5 feet on top of the RAB tool provides the
greatest constructive interference, i.e., an amplification factor of approximately
1.7 (sensitivity analyses, performed with minor adjustments to the assumed
parameters, lead to similar conclusions). The “1.7” factor is relevant, of course,
assuming that a good underlying signal can be created and that turning torques
are not high - these, in turn, require detailed short and intermediate wind tunnel
siren design and analysis.