R&S ESR Series User Manual page 339

®
R&S ESR
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
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
the AM Modulation
surement manually in
Modulated Carrier (Span >
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
FUNCtion:MDEPth:RESult?
Softkeys for AM Modulation Depth Measurements
AM Mod
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.
User Manual 1175.7068.02 ─ 12
Depth", on page 1008 and an example of how to perform the mea-
Chapter 3.5.3.2, "Measuring the Modulation Depth of an AM-
0)",
Depth............................................................................................................ 336
└ Marker 1 / Marker 2 / Marker 3 / ... Marker 16,/ Marker
└ Search Signals..............................................................................................337
on page 103.
CALCulate<n>:MARKer<m>:
on page 784.
Spectrum Measurements
Measurements
AM Mod Depth
Chapter 11.17.2.3, "Measuring
Norm/Delta............ 337
336