During application, how to determine and set the sampling rate of the vector signal analyzer?

For a vector signal analyzer, when it is not in record (or transient capture) mode, the sampling rate is determined by the interval selected by the user. For zoom time (i.e., the start frequency is not 0 Hz), the formula is:

Sampling rate (Hz) = 1.28 × user-set time interval.

For baseband time (for example, starting at 0 Hz), the formula is:

Sampling rate (Hz) = 2.56 × user-set time interval.

To change the sampling rate to your desired value (e.g. 20MHz in 89600s scaled time), simply adjust the time interval to:

20 MHz/1.28 = 15.625 MHz。

By setting a marker on the first data point of the Main Time trace (B after the preset), you can view the corresponding sampling time interval (50 nanoseconds).

However, in recording mode or transient capture mode, the sampling rate is usually calculated according to the following formula:

Sampling rate (Hz) = 1.28 or 2.56 × basic time interval,

Here, the constant depends on the scaling time or the baseband time.

The user can select the basic time interval from the front panel and define it as:

Maximum time interval/2n, where n is an integer.

If the user does not select a base interval, it will record the next higher base interval and that interval will determine the sample rate (or sampling interval). Unlike regular acquisition mode, you cannot play back the recording to see the sampling interval captured at that moment unless you choose to play back the base interval.

For example, you set the 89600S to a 20 MHz interval and make a recording. Since 20 MHz is not a base interval, the recording will be made at the next higher base interval (i.e. 37.109375MHz). You then choose to play back the recording at a 20 MHz interval and mark the first data point in the main time trace, the displayed sampling interval is 39.0625 nanoseconds. That indicates the sampling rate is:

1/39 nS=25.6MHz
or
1.28×20MHz=25.6MHz.

Note: Whether you select the regular data acquisition mode or the record/transient capture mode, the Raw Main Time data is outside the range of the digitizer and is usually the fundamental time interval. This data is incorrect. If the user selects a non-fundamental time interval to view the data, the instrument will resample in order to generate a two-digit FFT sample data.