Instrument Functions; Setting Of The Frequency (Freq); Aktivating/Parameterizing The Built In Tg; Frequency Range Displayed (Span) - Hameg HMS 3000 Handbuch

I n s t r u m e n t f u n c t i o n s

5 Instrument functions

5.1 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 chapter 4.
Spectrum display needs to be parameterised before measure-
ment is started. The two most important parameters are start
and stop frequency of the sweep. The start frequency sets the
frequency at the left border of the trace, the stop frequency
sets the highest frequency at the right hand border. In some
applications it is easier to modify the center frequency via the
CENTER key. In this case start and stop frequencies are auto-
matically adapted.
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.
5.2

Aktivating/parameterizing the built in TG

The output of the tracking generators is nominal 0 dBm. It can
be reduced via an adjustable TG attenuator in 1 dB steps up to
–20 dBm (tracking generator attenuation). The tracking gene-
rator generates an output signal on the same frequency which
is currently received by the analyzer.
It is strongly recommended to deactivate the tracking generator,
whenever it is not required for the measurement. With activated
tracking generator, the instrument is not able to compensate
all imperfections any more. This will be indicated with a red „TG
on" message on the bottom right of the display, as well as a
UNCAL message at the top of the display. The UNCAL message
disappears, once the trace mathematics (Chapter 5.7.1) of the
HMS is used to compensate the effects described above.
Performing measurements with the tracking generator
One of the most common application for TG measurements is
the spectral investigation of hardware components. For this
purpose, the DUT (device-under-test) is looped into the signal
path between TG output and receiver input. In order to com-
pensate 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 interference of the cables, con-
nectors, etc. and needs to be stored in the trace memory of the
spectrum analyzer. Afterwards the trace mathematics (TRACE
- MEM) shall be activated. Due to the mathematical compensa-
tion of all interferences, necessarily a straight line is displayed
and the UNCAL message is removed. After connection of the
42
Subject to change without notice
DUT into the signal path, the frequency response of the DUT is
shown at the display, based on the selected frequency range.
The signal output of the tracking generator of the HMS1010/3010
shows no „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 GHz/3 GHz, is not
absolutely necessary to provide the desired function. The
shape of the signal output is frequency dependend. For the
„interpretation" at the input of the HMS does not require a
sinusoidal signal curve.
Through the reduction of the TG output signal to the input and
the use of HMS (view in relation) narrow-band filter, neither the
shape nor the signal harmonics of the signal are evaluated. The
correct function of the TG by using the HMS is ensured at any time.
Since the existing tracking generator have to display frequencies
in a very broad context, it is customary that the tracking gene-
rator can not display low frequency signals (frequency range
5 MHz to 1 GHz resp. 3 GHz).
5.3 Frequency range displayed
(SPAN)
In principal there are two methods to define the displayed
frequency range: Defining start and stop frequency or center
frequency and span. The frequency range called span is the
range on both sides of the center frequency which a spectrum
analyzer displays on its screen. The span to be selected depends
on the signal to be analyzed, in general, it should be at least
twice as wide as the bandwidth of the signal.
The HMS series offers spans from 1 kHz to 1 GHz (HMS1000/1010)
resp. from 100 Hz to 3 GHz (HMS3000/3010).
Fig. 5.1: Hf signal modulated by a sine wave signal and the
resultant video signal vs. time
In zero span mode the spectrum analyzer acts similar to a
receiver tuned to the center frequency. In this case the trace
display does not represent a spectrum but the amplitude over
time. In other words the spectrum analyzer behaves like a
selective oscilloscope. In order to select the full (maximum)
frequency range of 100 kHz to 1 GHz resp. 100 Hz to 3 GHz by
pushing once, the soft menu item FULL is provided. The soft
menu key LAST will restore the former setting (the last span
setting). The setting is performed as described in chapter 4.
5.4 Setting of the amplitude parameters
(AMPL)
The key AMPL is used for all settings of the amplitude displayed.
The reference level (soft menu item REF.LEVEL) is identical to
the top graticule line of the display. The setting is performed
as described in chapter 4.