Model 2701 User’s Manual Specifications A-9
Calculating dB characteristics accuracy
The relationship between voltage and dB is as follows:
As an example of how to calculate the actual readings limits for dB, with a user-defined
VREF of 10V, you must calculate the voltage accuracy and apply it to the above equation.
To calculate a -60dB measurement, assume 10mV RMS for a VREF of 10V. Using the
100mV range, one-year, 10Hz - 20kHz frequency band, and SLOW rate, the voltage limits
are as follows:
Accuracy = ±[(0.06% of reading) + (0.03% of range)]
±[(0.0006
×
10mV) + (0.0003
×
100mV)]
±(6µV + 30µV)
±36µV
Thus, the actual reading accuracy is 10mV ±36mV or 10.036mV to 9.964mV. Applying
the voltage reading accuracy into the dB equation yields:
Thus, the actual reading accuracy is -60dB + 0.031213dB to -60dB - 0.031326dB.
dBm and dB for other voltage inputs can be calculated in exactly the same manner using
pertinent specifications, ranges, and other reference voltages.
Additional derating factors
In some cases, additional derating factors must be applied to calculate certain accuracy
values. For example, an additional derating factor of 0.02ppm/V must be added to DCV
specifications for voltages over 500V. Before calculating accuracy, study the associated
specifications very carefully to see if any derating factors apply.
dB 20
V
IN
V
REF
------------
log=
dBm 20
10.036mV
10V
--------------------------
log 59.96879dB–==
dBm 20
9.964mV
10V
-----------------------
log 60.03133dB–==
Appendix A.fm Page 9 Tuesday, July 22, 2003 11:10 PM
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