to make a selection. This feature is provided as a
rapid means of setting both cable loss and propa-
gation velocity.
q
WINDW
— Opens a menu of FFT windowing
types for the DTF calculation. Use the Up/Down
Arrow key and ENTER key to make a selection.
NOTE: Using Windowing
The theoretical requirement for inverse FFT is for the
data to extend from zero frequency to infinity. Side
lobes appear around a discontinuity due to the fact
that the spectrum is cut off at a finite frequency. Win-
dowing reduces the side lobes by smoothing out the
sharp transitions at the beginning and end of the fre-
quency sweep. As the side lobes are reduced the
main lobe widens thereby reducing the resolution.
In situations where there may be a small discontinuity
close to a large one, side lobe reduction Windowing
should be used. When distance resolution is critical
Windowing can be reduced. The types of Windowing
in order of increasing side lobe reduction are: rectan-
gular, nominal side lobe, low side lobe, minimum side
lobe. Figures 2-4 thru 2-7, on pages 2-14 and 2-15,
are examples of the types of Windowing.
q
MAIN
— Returns to the Main Menu.
2 - 13
Chapter 2 Operation