R&S NRP2, User Manual

Page: 85 / 437

Instrument Functions
R&S
®
NRP2
67 User Manual 1173.9157.02 ─ 03
The more modulation periods fit into an acquisition interval, the less critical it is whether
N is an integer or not. With smoothing on, about five periods are enough to reduce fluc-
tuations caused by modulation to an acceptable level - if N is not an integer. With more
than nine periods, the fluctuations are imperceptible. With smoothing off, the situation is
much less favorable as instead of just five periods as many as 300 are required; the
fluctuations only completely disappear with more than 3000 periods.
It is not useful to select the aperture time longer than required, since it increases the noise
component of the power sensor (
​
chapter 4.2.1.7, "Background information on power
measurement" , on page 72).
SCPI command:
​
[SENSe<[1]..4>][:
​
POWer][:
​
AVG]:
​
APERture
​
on page 270
Sampling rate
Sets the sampling rate. With the multipath power sensors R&S NRP-
Z11/21/22/23/24/28/31/32, the sampling rate can be set to two different values to prevent
aliasing effects for particular types of modulation signal. Aliasing can occur because the
sampling frequency is located within the video bandwidth, which means that spectral
components near the sampling frequency can cause beating effects. With changing the
sampling rate, the beating effects usually disappear.
SCPI command:
​
[SENSe<[1]..4>]:
​
SAMPling
​
on page 277
Duty Cycle
Using the duty cycle correction, the average power of RF bursts is calculated from the
average power of the whole signal. Essentially, the average power of the whole signal is
divided by the set duty cycle.
If thermal power sensors or R&S NRP-Z91/98 multipath power sensors are used, this
procedure is the only way to determine the power of pulsed signals.
If multipath power sensors R&S NRP-Z11/21/22/23/24/28/31/32 are used, this method
must be employed if the bursts are so short that their power cannot be measured in the
"Burst Av" or "Timegate Av" modes.
SCPI command:
​
[SENSe<[1]..4>]:
​
CORRection:
​
DCYCle:
​
STATe
​
on page 266
​
[SENSe<[1]..4>]:
​
CORRection:
​
DCYCle[:
​
INPut][:
​
MAGNitude]
​
on page 266
Smoothing of modulated signals
To reduce result fluctuations caused by modulation, this parameter should always be
activated if the aperture time cannot be exactly adjusted to the modulation period. If the
aperture time is only 5 to 9 times larger than a modulation period, the display fluctuations
are sufficiently reduced. With smoothing off, 300 to 3000 periods would be required to
obtain the same effect (
​
"Aperture" on page 66).
SCPI command:
​
[SENSe<[1]..4>][:
​
POWer][:
​
AVG]:
​
SMOothing:
​
STATe
​
on page 271
Data acquisition and parameters