Decibel (Db) - Fluke 8060A Instruction Manual

8060A
Instruction Manual

2-24. Decibel (dB)

The selection of dB is described in Figure 2-19. Like frequency, dB is
automatically canceled if you select another function (resistance or
frequency, for example).
When dB is selected, the 8060A microcomputer converts ac or dc voltage
readings to the dBm equivalent (decibels above or below one milliwatt). The
standard reference impedance is 600 . You can make dB measurements
independent of the reference impedance by using the relative function in
conjunction with the dB function. You can also modify the reference
impedance by applying and storing a voltage equivalent to 0 dBm referenced
to the desired impedance. Refer to Chapter 3 for details.
Note that the 8060A performs a 'bridging' measurement when measuring
dBm, which assumes the reference load is part of the system. When making
'terminating' measurements (such as testing a phone line without a phone
connected) be sure to apply the proper load to the 8060A. For example, if
you are making a terminating dBm measurement in a 600 system with 50V
maximum signal levels, place a 600 5 watt resistor across the 8060A input
terminals.
The ac dB dynamic range is from -50.0 to 59.72 dBm (109.72 dBm total).
The dc dB dynamic range is from -74 to 62.22 dBm (136.22 dBm total). For
readings greater than approximately 5% of full-scale for the voltage range
selected, the resolution is .01 dB. Below approximately 5% of scale,
resolution drops off to .1 dB, and below approximately 0.6% of scale,
resolution is 1 dB. Anytime blank digits appear to the right of the decimal
point, it is an indication that resolution has fallen off and you need to select a
lower range.
2-30