Keithley 2000 Calibration Manual

Calculating dBm characteristics accuracy
As an example of how to calculate the actual reading limits for a 13dBm measurement with
a reference impedance of 50
Ω , assume an applied signal 0.998815V. The relationship between
voltage and dBm is as follows:
From the previous example on calculating DC characteristics accuracy, it can be shown that
0.998815V has an uncertainty of
± 36.96445 µ V, or 0.998778V to 0.998852V, using one-year
specifications of the 1VDC range.
Expressing 0.998778V as dBm:
and expressing 0.998852V as dBm:
Thus, the actual reading range is 13dBm
± 0.00032dBm.
dBm and dB for other voltage inputs can be calculated in exactly the same manner using per-
tinent specifcations, ranges, and reference impedances.
dBm = 10 log
V
2
IN
/ R
REF
1mW
----------------------------
dBm = 10 log
0.998778V()
2
/ 50Ω
1mW
------------------------------------------------- 13.00032dBm=
dBm = 10 log
0.998852V()
2
/ 50Ω
1mW
------------------------------------------------- 13.00032dBm=
A-8 Specifications

Keithley 2000 Specifications

General

Digits	6.5
DC Voltage Range	100 mV to 1000 V
AC Voltage Range	100 mV to 750 V
Resistance Range	100 Ω to 100 MΩ
Connectivity	IEEE-488 (GPIB)
Display Type	VFD