NF FRA5097, Instruction Manual

Page: 73 / 192

3.5 Examples of basic operations
FRA5097 3-33
3.5.5 High frequency measurement
At frequencies above 1 MHz, measurement error increases with greater frequency. Following
are points to be considered when measuring high frequencies.
a) Measuring mode
Since error increases in measuring modes (CH1, OSC) and (OSC, CH2), use (CH1, CH2). The
increase is due to the different signal paths of these modes.
b) Analysis mode
When measuring signal voltage in analysis mode CH1 or CH2, error increases at frequency
exceeding about 2 MHz.
c) Auto ranging
The FRA5097 internal measuring range automatically corresponds to the signal size. Since
calibration error increases at high frequency, the measurement graph may show small steps before
and after range selection.
d) Use correct probe
At high frequency, electrostatic capacitance of the cable greatly affects the system under test
(SUT). Also, signal reflection due to impedance mismatch can increase measurement error. In
these type situations, the use of a suitable probe to reduce measurement error is recommended.
For example, a 10:1 oscilloscope probe can be used. Select a probe with an oscilloscope
matching impedance in the range of 20 to 30 pF at 1 M
Ω
. Before measuring, adjust the probe
trimmer for flat frequency response.
While using the probe to measure an oscillator output, adjust the trimmer to where the voltage (or
ratio) at 100 kHz is equal to the voltage (or ratio) at 10 Hz. Use Repeat measurement and first
measure the voltage (or ratio) at 10 Hz.
According to the probe type and trimmer initial setting, a lower reference frequency is desirable.
By using a 10:1 probe, the signal is attenuated 1/10. But this can be largely compensated by
using a weighting factor 10 at the analyzer input.
By using a 10:1 probe, the signal is attenuated 1/10. But this can be largely compensated by
using a weighting factor 10 at the analyzer input.
See 4.4 Input setting [Weighting factor].
The FRA5097 equalizer function can be used to compensate the probe error correction.
See 4.7 Equalization
By applying a feed through type 50
Ω terminator to the FRA5097 signal input
terminal, a 500 Ω input impedance high frequency 10:1 probe can also be used.