Practical_Antenna_Handbook_0071639586

128 P a r t I I : F u n d a m e n t a l s
Figure 4.7B Test setup for impromptu time domain reflectometry.
closer look is provided in Fig. 4.7C. A BNC “tee” connector and a double male BNC
adapter are used to interconnect the box with the ’scope.
If a periodic waveform is supplied by the generator, the display on the oscilloscope
will represent the sum of reflected and incident pulses. The duration of the pulse (i.e.,
pulse width), or one-half the period
of the square wave, is adjusted so
that the returning reflected pulse
arrives approximately in the center
of the incident pulse.
The images of Fig. 4.8 are TDR
displays for several different values
of Z L . Approximately 30 m of
coaxial cable with a velocity factor
of 0.66 was used in a test setup
similar to that shown in Fig. 4.7.
The pulse width was approximately
0.9 μs (microseconds). The
horizontal sweep time on the
’scope was adjusted to show only
one pulse—which, in this case,
represented one-half of a 550-kHz
square wave (Fig. 4.8B).
Figure 4.7C Close-up of RF
connections.