The calculation ofdBm is slightly more complicated, according to the
following formula:
where V is the measured voltage, R is the programmable impedance,
and Pr is 1 milliwatt. The log calculation is to the base 10.
The impedance used for Watt calculations is remembered separately
from the impedance used for dBm calculations. To set the impedance
references, go to the Analyzer Only Panel and select dBm or W for the
main measurement units using the upper left soft key. Then the
reference impedance for the selected unit will be shown across the
center ofthe display and the AMPLITUDE controls may be used to
change it.
Frequency units
.
Hz – hertz, basic unit offrequency (1/sec)
.
% - Percentage variation in frequency
.
∆
% - Percentage deviation from ideal frequency
Hertz (abbreviated Hz) is the basic unit offrequency. It is a count of
the number ofcycles a waveform goes through in a second. It is the
reciprocal ofthe number ofseconds required for one cycle ofa
waveform.
The % (percent) unit is used in the Wow and Flutter measurement
function to measure the variation in frequency. The Wow and Flutter
detector measures the frequency variation and reduces it to a number
in Hertz, according to the selected detector and statistical choices. This
variation is then calculated as a percentage ofthe 3 kHz or 3.15 kHz
intended frequency using the following formula:
where D is the frequency deviation and F is the intended frequency.
dBm
V R
=
•
10
2
log(
Pr
)
%
=
FH IK
•
abs
D
F
100
&
For
information
about dBm and
dBu units, see
page 4-73.
&
For
information on
moving among
the panels, see
page 4-1.
4
Oper
ati
o
n
Units : Frequency units
Operation
Portable One Plus Access User's Manual
4-75
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