Instrument Functions; Setting Of The Frequency (Freq); Aktivating / Parameterizing The Built-In Tracking Generator (Tg) *) - Rohde & Schwarz HMS-X Benutzerhandbuch

6 Instrument
Functions
6.1

Setting of the frequency (FREQ)

Pushing the FREQ key will call the menu for setting the fre-
quency. The setting is performed as described in chapt. 5.
Spectrum display needs to be parameterised before mea-
surement is started. The two most important parameters
are start and stop frequency of the sweep. The frequency
can be specified in terms of the center frequency (cen-
ter freqency = frequency at the center of the frequency
axis in the measurement diagram) or the start and stop
frequency for a particular span. The start frequency sets
the frequency at the left border of the trace, the stop fre-
quency sets the highest frequency at the right hand bor-
der. In some applications it is easier to modify the center
frequency. In this case start and stop frequencies are auto-
matically adapted. It is best to enter the center frequency
when a signal is to be measured at a known frequency.
When you are investigating signals, e.g. harmonics, that
are within a particular frequency range, the best option is
entering a start and stop frequency to define the span.
The step size of the center frequency can be modified with
CF-STEPSIZE. By pushing this soft menu key the settings
menu will open.
❙ 0.1 x SPAN (Basic setting): The step size is always 1/10 of
the currently selected span (= 1 vertical division).
❙ 0.5 x SPAN: The step size is always 1/2 of the currently
selected span (= 5 vertical divisions).
❙ SET TO CENTER: The step size of the frequency is equal
to the present center frequency. This mode is especially
useful for the measurement of harmonics because each
step will move the center frequency to the next harmonic.
❙ MANUAL: Any step size is available. This allows the easy
measurement of spectra with regular frequency steps.
6.2 Aktivating / parameterizing the built-in
tracking generator (TG) *)
„Tracking" of a tracking generator means the genera-
tor fundamental frequency is in the center of the analyzer
passband at every instant of time. The tracking generator
sweeps the entire available frequency range depending on
the current measurement frequency of the spectrum ana-
lyzer. The tracking generator allows the user to perform
frequency measurements for filters, amplifiers or mixers,
for instance. With this system, it is also possible to mea-
sure reflection coefficients or return loss and consequently
also investigate voltage standing wave ratios (VSWR). The
output signal of the tracking generator is transmitted at the
component to be examined, and the output voltage is ap-
plied to the spectrum analyzer input. The output of the tra-
cking generator is nominal 0 dBm. It can be reduced via
an adjustable TG attenuator (TG Att) in 1 dB steps up to
–20 dBm (tracking generator attenuation). The tracking ge-
nerator generates an output signal on the same frequency
which is currently received by the analyzer.
It is recommended to deactivate the tracking generator,
whenever it is not required for the measurement. With ac-
tivated tracking generator, the instrument is not able to
compensate all imperfections anymore. This will be indica-
ted with a red „TG on" message on the bottom right of the
display, as well as a UNCAL message at the top of the dis-
play. The UNCAL message disappears, once the trace ma-
thematics (please refer to chapter 6.7.1) of the R&S®HMS-X
is used to compensate the effects described above.
6.2.1 Performing measurements with the TG
One of the most common application for TG measure-
ments is the spectral investigation of hardware compo-
nents. For this purpose, the DUT (device-under-test) is
looped into the signal path between TG output and recei-
ver input. In order to compensate any influences caused
by cables, adaptors etc. used at the application, these will
be directly connected to the spectrum analyzer without
the DUT in the loop. The resulting trace shows the inter-
ference of the cables, connectors, etc. and needs to be
stored in the trace memory of the spectrum analyzer. Af-
terwards the trace mathematics (TRACE - MEM) shall be
activated. Due to the mathematical compensation of all in-
terferences, necessarily a straight line is displayed and the
UNCAL message is removed. After connection of the DUT
into the signal path, the frequency response of the DUT
is shown at the display, based on the selected frequency
range.
The UNCAL message disappears by using the trace math.
The signal output of the tracking generator does not show
a "true" sine wave signal. The output signal of the TG is
generally not sinusoidal in even spectrum analyzers from
other manufacturers. A generator which can generate a
uniform sinusoidal signal from 5 MHz to 1.6 GHz/3 GHz,
is not absolutely necessary to provide the desired func-
tion. The shape of the signal output is frequency depen-
dend. A sinusoidal signal curve is not required for the "in-
terpretation" at the R&S®HMS-X input. Through the re-
duction of the TG output signal to the input and the use
of R&S®HMS-X (view in relation) narrow-band filter, neit-
her the shape nor the signal harmonics of the signal are
evaluated. The correct function of the TG by using the
R&S®HMS-X is ensured at any time. Since the existing tra-
cking generator has to display frequencies in a very broad
context, it is usually that the tracking generator can not
display low frequency signals (frequency range 5 MHz to
1.6 GHz resp. 3 GHz).
Further information about the TG in combination with the
trace math you can find in chapter 6.7.2.
*) only available in combination with R&S®HMS-TG resp. R&S®HV211

Instrument Functions

*)
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