Operating instructions

University of Saskatchewan
Electrical Engineering Laboratory Equipment Manual
large number of averages, in the exponential mode, will not capture any changes in the
signal.
The SOURCE menu selects the output waveform. The Configure Source
submenu sets the parameters. The 2-Tone waveform is the sum of two pure sine waves
for intermodulation distortion tests.
The Chirp source provides an equal amplitude sine wave at each bin of the
span. The phases of the sine waves are set so that they do not add in phase. This
source is used to measure transfer functions (frequency response). The waveform is
periodic over the time record and does not require windowing. Use the Uniform window
and the Src (source) trigger. Turn the Auto Offset off in the input menu. The source is
digitally synthesized and has an output filter. The ripple of this filter appears at the
output. Source Cal compensates for the output ripple by adjusting the input
calibrations. The signal at the source output is not adjusted. If a device is inserted
between the source and the input, the amplitude frequency response of the device will
be displayed. The Auto Phase key performs the auto phase function. With Src (source)
trigger, the phases of the sine waves of the source are stable but random. A calibrated
source phase curve is required to measure the phase of a device under test. The auto
phase function measure the current phase spectrum of the source and then subtractes
it from the next phase spectrum to remove the phase from the source. With Auto
Phase, the phase spectrum will be 0 degrees across the span. If a device is inserted
between the source and the input, the phase spectrum will be the phase response curve
of the device under test. Auto Phase is turned off whenever the span or source type is
changed.
NOTE: A inherent problem exists when a frequency response is done with a
small linewidth. Errors may occur if the start frequency is not at zero or Center (on the
marker keypad) is used. Detail expansion of the frequency span can be done using
Expand X (zoom) with no errors. Ensure the frequency of interest is at the center of a
bin. It is always best to know the expected output. An analog spectrum analyzer with a
sine source is a more accurate analyzer to use for a frequency response.
Frequency Response Summary
- Use Chirp source.
- Uniform window.
- Source Cal.
- Trigger Src.
- Auto Offset off ( Input menu).
- Auto Phase optional.
- Start frequency at zero.
- Do not use Centre on Marker keypad.
- Place Marker on centre frequency and use Expand X.