Rohde & Schwarz R&S UPP, User Manual

Page: 392 / 938

Instrument Functions
R&S
®
UPP
376 User Manual 1411.1055.32 ─ 10
For signal-to-noise measurements, the internal Universal Generator must be used,
since an external generator cannot be controlled by the measurement function. If the
DUT is inadvertently not connected to the internal generator, measured values of
around 0 dB would be determined.
The signal for noise measurement is generated by an analog or digital generator
depending on the DUT:
●
In the case of an analog generator instrument, the generator output voltage is
switched off and the output impedance remains unchanged.
●
In the case of digital generator instruments, a level value of 0.0 fullscale is output
with an unchanged clock rate (all bits on 0).
If the analog universal generator is used, care must be taken to ensure that the correct
Volt Range is selected on the Generator Config Panel (see
Chapter 5.2.1, "Analog
Generator Config Panel" , on page 196). In Auto mode the analog gain is canceled dur-
ing noise measurement, which on the one hand brings about an improvement in the
inherent noise (and therefore in the S/N dynamic response), but on the other hand
results in a longer measurement time.
The level weighting method can be chosen from the following:
●
RMS: Root-mean-square broadband measurement
●
Peak: Peak-value measurement.
When the analog analyzer is used, switching off the generator causes a DC jump at
the analyzer input, and this must not be allowed to affect the highly sensitive noise
measurement.
There are two measures which will solve this problem:
●
The S/N measurement should preferably be carried out using a low-frequency
highpass or comparable weighting filter. Failing to use a suitable filter will result in
an error message.
●
For measurement at low frequencies, where a highpass filter cannot be used, the
recommended alternative is a file-defined delay filter with around 1.5 s of delay.
This allows the DC jump to decay before the noise measurement starts.
S/N measurement can be performed via the S/N measurement function. This measure-
ment function is found at menu item "Meas Mode" and offers a choice of level weight-
ing methods.
Conversely – as with the previous products, R&S UPD, R&S UPL and R&S UPV –
the S/N sequence can also be activated during level measurements. This alternative
operating mode ensures compatibility with the earlier models mentioned, and in partic-
ular enables remote-control programs to be used unchanged.
Signal-to-Noise Measurements