R&S ESR Series User Manual

Spectrum Measurements
R&S
®
ESR
336User Manual 1175.7068.02 ─ 12
6.1.1.12 Measuring the AM Modulation Depth
The AM modulation depth, also known as a modulation index, indicates by how much
the modulated signal varies around the carrier amplitude. It is defined as:
MDepth = peak signal amplitude / unmodulated carrier amplitude
So for MDepth = 0.5, for example, the carrier amplitude varies by 50% above and
below its unmodulated level, and for h = 1.0 it varies by 100%.
You can measure the modulation depth of a modulated signal using the AM Mod Depth
function.
When this function is activated, marker 1 is set to the peak level, which is considered
to be the carrier level. Deltamarkers 2 and 3 are automatically set symmetrically to the
carrier on the adjacent peak values of the trace. The markers can be adjusted man-
ually, if necessary.
The R&S ESR calculates the power at the marker positions from the measured levels.
The AM modulation depth is calculated as the ratio between the power values at the
reference marker and at the delta markers. If the powers of the two AM side bands are
unequal, the mean value of the two power values is used for AM modulation depth cal-
culation.
A remote control programming example is described in Chapter 11.17.2.3, "Measuring
the AM Modulation Depth", on page 1008 and an example of how to perform the mea-
surement manually in Chapter 3.5.3.2, "Measuring the Modulation Depth of an AM-
Modulated Carrier (Span > 0)", on page 103.
Measurement results
The AM modulation depth in percent is displayed as a result of the measurement, indi-
cated in the marker results as "MDepth".
It can also be queried using the remote command CALCulate<n>:MARKer<m>:
FUNCtion:MDEPth:RESult? on page 784.
Softkeys for AM Modulation Depth Measurements
AM Mod Depth............................................................................................................ 336
└ Marker 1 / Marker 2 / Marker 3 / … Marker 16,/ Marker Norm/Delta............ 337
└ Search Signals..............................................................................................337
AM Mod Depth
Activates the measurement of the AM modulation depth. An AM-modulated carrier is
required on the screen to ensure correct operation.
When this function is activated, marker 1 is set to the peak level, which is considered
to be the carrier level. Deltamarkers 2 and 3 are automatically set symmetrically to the
carrier on the adjacent peak values of the trace. An edit dialog box is displayed for del-
tamarker 2 in order to adjust the position manually.
When the position of deltamarker 2 is changed, deltamarker 3 is moved symmetrically
with respect to the reference marker 1.
Measurements

R&S ESR Series Specifications

General

Brand	R&S
Model	ESR Series
Category	Receiver
Language	English