Rohde & Schwarz UPD - Page 30

1GA16_1L.DOC ROHDE & SCHWARZ29
or after the start of the signal travel time
( )/
/
f f Hz
d m
2 1
165
− <
Same as with sound pressure measurements, the microphone distance is entered with the DISTANCE
softkey (F8, level 4) in the MICROPHN menu. The distance entered in this menu is used as a default
value (see DISTANCE in section 5.2.3, Entry of Microphone Parameters). The program calculates the
sweep steps from the distance of the microphone according to the formula
( )/
/
f f Hz
d m
2 1
150
− =
Note that the microphone should not be set up too far away as otherwise the desired frequency range
cannot be covered with the maximum permissible sweep points (1024). The condition
f f Hz
d m
stop start
− < ⋅/
/
1023
150
should be fulfilled, or for the microphone distance
d m
f f Hz
stop start
/
/
<
−
153450
Example: A microphone distance of 1 m and a frequency sweep of 20 to 20000 Hz yield a frequency
increment of 150 Hz and therefore 135 sweep points. As the example shows, this restriction has
relevance only in theory.
If the sweep should be carried out with a greater number of points than required by the microphone
distance, this can be obtained by entering SWP PNTS (F8, level 3, see section 3.4, Entry of
Parameters).
The display mode can be selected either before the sweep is started or after its termination (see section
5.3.3, Linearity Departure and Group Delay).
Note: In the case of phase measurements, only DISTANCE is offered in the MICROPHN menu; all
other microphone parameters are irrelevant.