76 Chapter 2
Making Complex Measurements
Making Stimulus Response Measurements
Tracking Generator Unleveled Condition
When using the tracking generator, the message TG unleveled may
appear. The TG unleveled message indicates that the tracking
generator source power (Source, Amplitude) could not be maintained at
the selected level during some portion of the sweep. If the unleveled
condition exists at the beginning of the sweep, the message will be
displayed immediately. If the unleveled condition occurs after the sweep
begins, the message will be displayed after the sweep is completed. A
momentary unleveled condition may not be detected when the sweep
time is short. The message will be cleared after a sweep is completed
with no unleveled conditions.
The unleveled condition may be caused by any of the following:
•Start frequency is too low or the stop frequency is too high. The
unleveled condition is likely to occur if the true frequency range
exceeds the tracking generator frequency specification (especially
the low frequency specification).
•Source attenuation may be set incorrectly (select Attenuation (Auto)
for optimum setting).
•The source power may be set too high or too low, use Amplitude (Off)
then Amplitude (On) to reset it.
•The source power sweep may be set too high, resulting in an
unleveled condition at the end of the sweep. Use Power Sweep (Off)
then Power Sweep (On) to decrease the amplitude.
•Reverse RF power from the device under test detected by the
tracking generator ALC (aut o m a tic level control) system.
Measuring Device Bandwidth
It is often necessary to measure device bandwidth, such as when testing
a bandpass filter. There is a key in the Peak Search menu that will
perform this function. The device signal being measured must be
displayed before activating the measurement. The span must include
the full response.
Activate the measurement by toggling the N dB Points key to On. The
analyzer places arrow markers at the −3 dB points on either side of the
response and reads the bandwidth. For other ba ndwidth responses
enter the number of dB down desired, from −1 dB to −80 dB.
No other signal can appear on the display within N dB of the highest
signal. The measured signal cannot h av e more than one peak that is
greater than or equal to N dB. A signal must have a peak greater than
the currently defined peak excursion to be identified. The default value
for the peak excursion is 6 dB.