User manual

dBm is defined as decibels above or below a 1mW reference. With a user-programmable

reference impedance, the Model 2000 reads 0dBm when the voltage needed to dissipate

1mW through the reference impedance is applied. The relationship between dBm, a refer

ence impedance, and the voltage is defined by the following equation:

Where: V

is the DC or AC input signal.

REF

is the specified reference impedance.

NOTE Do not confuse reference impedance with input impedance. The input impedance

of the instrument is not modified by the dBm parameter.

If a relative value is in effect when dBm is selected, the value is converted to dBm then

REL is applied to dBm. If REL is applied after dBm has been selected, dBm math has REL

applied to it.

To set the reference impedance, perform the following steps:

1. After selecting dBm, the present reference impedance is displayed (1-9999Ω):

REF: 0000

2. To change the reference impedance, use the and keys to select the numeric

position. Then use the and keys to select the desired value. Be sure to press

ENTER after changing the reference impedance.

NOTES dBm is valid for positive and negative values of DC volts.

The mX+b and percent math operations are applied after the dBm or dB math. For

example, if mX+b is selected with m=10 and b=0, the display will read 10.000 MXB

for a 1VDC signal. If dBm is selected with Z

REF

= 50Ω, the display will read

130MXB.

dBm = 10 log

REF

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⎛⎞

1mW

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2000-900 (J - Aug 2010) BOOK.fm Page 32 Wednesday, October 12, 2011 12:29 PM