Time Records
As mentioned in Terminology Used in FFT Analyzers, a time record is the amount of time-domain data the analyzer needs to perform one FFT operation. The time record and its FFT are the building blocks the analyzer needs for all subsequent measurements.
Why is a time record needed?
Essentially, the time record is a block of time-domain sample points. Because the actual Fourier Transform does not have explicit time or frequency references (it simply operates on a sequential collection of points), FFT analyzers must assign arbitrary start and finish times for data to be transformed. These blocks of input data are called time records.
For example, with the default display resolution of 401 frequency points, the analyzer takes up to 1024 samples of time data to produce 512 points of frequency domain data. The analyzer usually displays the first 401 points of this data and discards the rest (this accommodates the anti-aliasing filters, but that's beyond the scope of this discussion).
The time record can be described by both a length and a size. The time record length is the amount of time required to acquire a time record and is altered by changing resolution bandwidth, window, main length, or gate length. The time record size is the number of time points in the time record and is dictated by the time record length in combination with the sample rate (and sample rate, in turn, is directly related to span).
Time record size refers to the number of time points (samples) in a time record. Time record length refers to the amount of time needed to acquire a time record.
See Also
