Keithley 2701, Руководство пользователя

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A-8 Specifications Model 2701 User’s 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 of 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 a measurement of 0.998815V on the 1V range has an uncertainty of ±36.9644mV or
0.998778V to 0.998852V, using one-year specifications.
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
pertinent specifications, ranges, and reference impedances.
dBm
10
V
2
IN
R
REF
⁄
1mW
------------------------------- log =
dBm
10
0.998778V
( )
2
50
Ω ⁄
1mW
---------------------------------------------------- log 12.99968dBm = =
dBm
0.998852V
( )
2
50
Ω ⁄
1mW
---------------------------------------------------- 13.00032dBm = =
2701-900-01.book Page 8 Wednesday, August 3, 2011 9:43 AM