After observing how important it is to have the minimum amplitude 

 defined as accurately as possible, the experiment used in Section III.3.b 

 was repeated with the measurement interval surrounding the observed 

 minimum reduced to Ax/L equal to 0.39 inch (1 centimeter). Figure C-2 

 is a plot of the raw and corrected data for measurements taken in the 

 immediate vicinity of two node locations, L/2 apart. Two observations 

 can be made. First, the raw data show a slight discrepancy between the 

 minimum locations and, secondly, one cannot assume that the actual 

 minimum, i.e., the first harmonic amplitude, will fall where the raw 

 data minimum occurs. In order to ensure that the actual minimum loca- 

 tion is found, one must use the smaller measurement intervals for a 

 sufficient distance around the observed minimum to ensure the location 

 of the actual minimum to be occupied. By substituting the results obtained 

 from Figure C-2 into the calculations made in Section Ill.S.b, one will 

 calculate an average reflection coefficient of R = 0.90 which is much 

 larger than the reflection coefficient suggested by the raw data 

 (R - 0.62) and slightly higher than obtained from the corrected data 

 (R - 0.88) with a measurement interval of 4 inches (10 centimeters) 

 when the best fit value of R is chosen. The accuracy, using the more 

 refined acquisition system, does not produce, in this case, a far 

 superior product. To avoid the somewhat subjective and tedious curve 

 fitting procedure, the refined system of closely spaced measurements 

 near nodes is recommended. Figure C-2 shows how the amplitude at the 

 node as well as the location of the minimum amplitude itself is affected 

 by higher order wave harmonics. 



Through the use of a high-speed computer, the data can be quickly 

 examined and the resolution required may easily be obtained. The 

 computer program which was used for the computerized procedure for 

 determining the reflection coefficient is listed on the following pages. 

 With the preceding description of the program and the extensive use of 

 comments in the program this should be self-explanatory. 



33 



