The Use and Calibration of the Kern ME5000 Mekometer - SLAC ...

-
0
/
I-
ME5000 Operation
4&l 470 480 4Kl SW 510
fmqwncy (MHzl
Figure 5. Actual Characteristic Curves for Instruments 357037 and 357081
For short-distance measurements, below 20 m, the normal 15 MHz bandwidth is insufficient (for
reasons explained below), so the intensity threshold is reduced to 75% of maximum to give a wider
bandwidth, nominally 30 MHz. In practice, this bandwidth is dependent upon the characteristics of the
individual crystal, and has been found to vary in the range 18 - 29 MHz. Table 1 shows the normal and
extended bandwidths for the two instruments shown in Fig. 5.
357037 (LBL)
357081. (SSC)
3.1 Normal Mode
Table 1. Modulation bandwidth of instruments 357037 and 357081
NORMAL. EXTENDED
Range (MHz) Bandwidth Rarqe (MHz) Bandwidth
472.112 - 486.915 14.803 465.383 - 494.644 28.261
472.785 - 486.915 14.130 469.420 - 490.280 20.859
3. RESOLVING THE DISTANCE
SLAC’s field measurement and data collection program ME5COO.BAS mimics the operation of the
onboard program in the ME5OOO’s EPROM for the measurement of distances in the normal operating range
of the instrument, 20 - 8000 m.
3.1.1. Calculation of distance from frequency
Starting at the lower end of the bandwidth an upward sweep is made until a frequency F1 is found at
which the phase difference is zero. This nodal point occurs when there is an integer number ml of half-
wavelengths along the measurement path. The sweep is continued until a second nodal point is found at
frequency Fl,.+ at which there are ml+1 half-wavelengths. The distance can be determined from the
frequency difference FM-FI, (S-10).
12
.