64 Keysight WLAN Measurement Guide
Making WLAN Measurements
Making Modulation Analysis Measurements
Optimizing EVM Measurements
The following sections describe how to optimize your analyzer settings and get
the best EVM measurements of OFDM signals.
Optimizing Input Level to ADC
You have control of 3 parameters to optimize the signal level to the ADC:
— Attenuation (mechanical and electronic attenuator if present),
— IF Gain
— Preamplifier
To achieve better EVM results, the instrument need the best balance between
distortion and signal-to-noise ratio, while avoiding Input Overload error.
There is a One Button Function to perform EVM optimization: press
Meas
Setup
,
Optimize EVM
.
If
Optimize EVM
is not available in your case, you can follow the steps below to
do it manually.
Optimize EVM
key is not available when
-
802.11b/g
is selected, or,
-
802.11ac 80MHz + 80MHz
is selected, or,
- Option B25 is only installed, or,
- N9000A CXA is used.
Steps
Action
Notes
For signals with power level around -10 dBm or higher
1.
Set the attenuator
automatically for
minimal clipping
a. Press
AMPTD
,
Attenuation
,
Adjust
Atten for Min Clip
.
The firmware limits the mechanical attenuator
from going below 6 dB to protect the input
from overloading.
2.
Manually adjust the
attenuator lower from
this level to improve the
EVM
a. Press
Mech Atten
and
enter the attenuation value
as suggested below.
The instrument will display a warning message
of "
Input overload; ADC Over
Range
" in the lower right corner of the display
if the attenuation value is too low.
For signals with power level around -20 dBm
1.
Reduce the mechanical
attenuator manually
down to 0 dB.
a. Press
Mech Atten
and
enter 0 dB.
For signals with power level around -30 dBm