Transient Constant Area Surface and Downhole Wave Models - Measurement While Drilling Signal Analysis, Optimization and Design - page 105

C Means 2*PI*F cycles in 2*PI secs, or F cycles per sec, F is
Hz.
C One cycle requires time PERIOD = 1./F
PERIOD = 1./F
IF(T.GE.0.0. AND.T.LE. PERIOD) G = +A*SIN(2.*PI*F*T)
IF(T.GE.PERIOD.AND.T.LE.2.*PERIOD) G = -A*SIN(2.*PI*F*T)
IF(T. GE.2.*PERIOD) G = 0.
x Roundtrip delay = 0.02 sec
x Sampling time = 0.001 sec
Figure 4.1f . 12 Hz low frequency carrier wave with phase shift keying.
Source code XDUCER*.FOR is used to produce the results of Method 4-1,
Run 3. A 12 Hz carrier wave is assumed. We phase-shift after one cycle; we
continue wave generation and turn off the pulser after two wave cycles. Note
the black upgoing clean signal in Figure 4.1f and the delayed reflected red
signal. The green signal combines both incident black and reflected red signals,
and appears somewhat like the black signal, except for two indentations on the
bottom (one for incident phase-shift and the second for the reflected phase-
shift). The “apparent phase shift” seen in the green signal is a somewhat
stretched valley. The green signal is a little wider than the original black signal
with taller humps and can be very confusing. The blue one is the deconvolved
signal using only input from the green data, and recovers the black one very
nicely, to include both the phase shift and the silent tail end of the signal.
Next, we consider a 24 Hz carrier wave, the higher carrier frequency
typically used in PSK schemes. This may transmit information at up to 6
bits/sec if attenuation is not problematic. In practice, the 'p siren signal
strength is weak and the transmitted signal attenuates over large distances. This
target data rate is almost never used in deep wells.
x Roundtrip delay = 0.02 sec
x Sampling time = 0.001 sec