Definition of drift signal

If the drift signal is measured with the spectrum analyzer, the center frequency should be changed in different period so as to facilitate observation. If the signal tracking function of the spectrum analyzer is enabled, the marker peak will always be displayed at the center frequency of the spectrum analyzer, thus facilitating measurement.

This section introduces how to measure the drift signal, in which the signal tracking function, marker function and maximum holding function of the spectrum analyzer are applied to observe the amplitude trace and occupied bandwidth of the drift signal.

 

Measurement of frequency drift for signal generator

The spectrum analyzer is able to measure the short-time and long-time stability of the signal generator. By using the maximum trace holding function, the spectrum analyzer can display the maximum peak amplitude and frequency drift of the input signal. The max hold function of track may be used to measure the occupied bandwidth of signal.

In this example, the signal tracking function of the spectrum analyzer is applied to keep the drift signal always displayed at the center and the maximum trace holding function to capture the drift.

 

1)       Set the output signal of the signal generator:

Set the signal generator to output the 300MHz and -20dBm signal. Connect the output of the signal generator to the input port of the spectrum analyzer, as shown in Fig. 4-1. Enable the RF output.

2)       Set the center frequency, span and reference level of the spectrum analyzer:

•  Press [Reset].

•  Press [Frequency], [Center Frequency], 300[MHz].

•  Press [frequency], [Span] and 10[MHz].

•  Press [Amplitude] , [Ref Level] and -10[dBm].

3)       Set the marker at the signal peak, and enable the signal tracking function.

•  Press [Peak] and [Peak Track Off On].

•  Press [Frequency] and  [Signal Track Off On].

4)       Reduce the span:

Press [Frequency], [Span] and 500 [kHz]. You can see that the signal is always at the center.

•  Disable the signal tracking function:

•  Press [Frequency] and [Signal Track Off On].

5)       Use the maximum holding function to measure the signal drift.

•  Press [Trace] and [Max Hold].s

When the signal changes, the max hold will maintain the maximum response to the input signal.

6)       Activate the trace 2 and set it into the continuous clearing and writing mode.

•  Press [Trace],  [Trace 1 2 3] and  [Clear Write].

7)       Change the output frequency of the signal generator.

Slowly change the output frequency of the signal generator, with the step of 1kHz and the range of ±50kHz. The spectrum analyzer will display the information shown in Figure below.

Observation of Drift Signal by Maximum Holding Function