User Manual

Spectrum Analysis
R&S
®
Scope Rider RTH
125User Manual 1326.1578.02 ─ 08
Converting voltage or Ampere to power values
The spectrum results are provided as voltages or in Amperes (depending on the probe
setting). To convert the these results (U/I) to power values (P), use the following equa-
tions:
)
V1
U
lg(20)U(P
dBV

)
A1
I
lg(20)I(P
dBA

)
1
R
lg(1030)U(P)mW1/
R
U
lg(10)
mW1
P
lg(10)U(P
dBV
2
dBm


)
1
R
lg(1030)I(P)
mW1
RI
lg(10)
mW1
P
lg(10)I(P
dBA
2
dBm




Where:
●
R = 50 Ω
●
P = U * I = U
2
/ R = I
2
* R
5.3 Harmonics Measurement (Option R&S RTH-K34)
With this measurement, you can easily measure the harmonics of an input signal. In
addition, the total harmonic distortion (THD) is calculated.
The harmonics measurement performs an FFT on the input signal and determines the
power levels measured at the specified fundamental frequency and at each harmonic.
Harmonics are frequencies that are a multiple of the fundamental frequency.
As a result, the magnitude, frequency and phase values for the selected harmonics are
shown, as well as the RMS power values and the total harmonic distortion (THD).
In general, every signal contains harmonics. Harmonics are generated by nonlinear
characteristics, which add frequencies to a pure sine wave. Harmonics are particularly
critical regarding high-power transmitters such as transceivers because large harmon-
ics can interfere with other radio services.
Harmonic distortion can be determined as the level of the individual components, or as
the root mean square of all components together, the total harmonic distortion (THD).
The THD is set in relation to the power of the fundamental frequency.
5.3.1 Accessing the Harmonic Mode
1. Press the MODE key.
Harmonics Measurement (Option R&S RTH-K34)