Rohde & Schwarz ESRP Series, Руководство пользователя

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Spectrum Measurements
R&S
®
ESRP
225 User Manual 1175.7445.02 ─ 08
The Adjust Settings softkey selects the RMS detector. This detector is selected
since it correctly indicates the power irrespective of the characteristics of the signal
to be measured. The whole IF envelope is used to calculate the power for each
measurement point. The IF envelope is digitized using a sampling frequency which
is at least five times the resolution bandwidth which has been selected. Based on
the sample values, the power is calculated for each measurement point using the
following formula:
where:
"s
i
= linear digitized video voltage at the output of the A/D converter"
"N = number of A/D converter values per measurement point"
"P
RMS
= power represented by a measurement point"
When the power has been calculated, the power units are converted into decibels
and the value is displayed as a measurement point.
In principle, the sample detector would be possible as well. Due to the limited num-
ber of measurement points used to calculate the power in the channel, the sample
detector would yield less stable results.
●
Trace averaging
The Adjust Settings softkey switches off this function. Averaging, which is often
performed to stabilize the measurement results, leads to a too low level indication
and should therefore be avoided. The reduction in the displayed power depends on
the number of averages and the signal characteristics in the channel to be mea-
sured.
●
Reference level
The Adjust Settings softkey does not influence the reference level. It can be adjus-
ted separately using the "Adjust Ref Lvl" softkey (see "Adjust Ref Lvl"
on page 222).
6.1.1.3 Measuring the Carrier-to-Noise Ratio
The R&S ESRP can easily determine the carrier-to-noise ratio, also normalized to a 1
Hz bandwidth.
The largest signal in the frequency span is the carrier. It is searched when the C/N or
C/NO function is activated (see
"C/N, C/No" on page 227) and is marked using a fixed
reference marker ("FXD").
To determine the noise power, a channel at the defined center frequency is examined.
The bandwidth of the channel is defined by the "Channel Bandwidth" setting. The
power within this channel is integrated to obtain the noise power level. (If the carrier is
within this channel, an extra step is required to determine the correct noise power
level, see below.)
The noise power of the channel is subtracted from the maximum carrier signal level,
and in the case of a C/NO measurement, it is referred to a 1 Hz bandwidth.
Measurements