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DC Detection
Measurements
Enabling the D
Detection Mode
Remember
Making Accurate D
Measurements
DC detection o ers absolute power measurement capability and the
ability to characterize oscillators and modulation sensitive devices.
1. On the analyzer, press
2. Connect the detector.
3. Enable DC mode:
Press
and select
SYSTEM 5
Selecting the
MODE DC
wave modulation.
You must enable the DC mode to access the DC-speci c softkeys.
o make DC-mode measurements as shown in Figure 3-2, you
must use an 85027 directional bridge capable of both AC and DC
detection.
Operation
Before accurate DC measurements can be made, two quick routines
must be performed; a DC zero and a dynamic power characterization.
( his is referred to as a power calibration on the 8757 and on other
annotations.) he DC zero will improve accuracy below
he dynamic characterization will provide the improved (corrected)
power accuracy speci cation on the 8787D Option 002 only.
Measurements can be performed without this characterization (such
as on instruments without Option 002), however only the default
dynamic accuracy speci cations of the detector are guaranteed. his
characterization includes a DC zero so it is not necessary to perform
the zero before performing the characterization.
Zeroing an 85037A/B
When making DC-mode measurements, you must perform a zeroing
operation to compensate for the e ects of DC drift and temperature
uctuations. his is not required in AC detection. he zeroing
operation eliminates small DC voltages present in the detector that
would otherwise cause amplitude measurement errors at low power
0
levels (
35 dBm and below). Zeroing also establishes the displayed
noise level (the system noise
oor) with no RF signal applied. A
DC zero should be performed at least once every half-hour once the
system has stabilized. A DC zero should be performed more often
as the system warms up, or if the temperature is changing. he
autozero function is provided to automatically perform DC zeros
periodically when the system interface is used.
.
PRESET 5
.
MODE DC
softkey also turns o the source square
0
35 dBm.
Operation 3-5
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