Rohde & Schwarz FSV3000, Руководство пользователя

Страница: 320 / 1489

Measurements and results
R&S
®
FSVA3000/ R&S
®
FSV3000
320 User Manual 1178.8520.02 ─ 08
5.12 AM modulation depth measurement
This measurement determines the AM modulation depth of an AM-modulated carrier.
● About the measurement ........................................................................................320
● AM modulation depth results .................................................................................321
● AM modulation depth configuration .......................................................................321
● Optimizing and troubleshooting the measurement ................................................323
● How to determine the AM modulation depth .........................................................323
5.12.1 About the measurement
The AM modulation depth, also known as a modulation index, indicates how much the
modulated signal varies around the carrier amplitude. It is defined as:
M
Depth
= peak signal amplitude / unmodulated carrier amplitude
So for M
Depth
= 0.5, for example, the carrier amplitude varies by 50% above and below
its unmodulated level, and for M
Depth
= 1.0 it varies by 100%.
When this measurement is activated, marker 1 is set to the peak level, which is consid-
ered to be the carrier level. Delta markers 2 and 3 are automatically set symmetrically
to the carrier on the adjacent peak values of the trace. The markers can be adjusted
manually, if necessary.
The R&S FSV/A calculates the power at the marker positions from the measured lev-
els. 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
calculation.
AM modulation depth measurement