Detector Types

Detector types
With digital displays, we had to decide what value should be displayed for
each display data point. No matter how many data points we use across
the display, each point must represent what has occurred over some
frequency range and, although we usually do not think in terms of time
when dealing with a spectrum analyzer, over some time interval.

Figure 2-17. When digitizing an analog signal, what value
should be displayed at each point?

It is as if the data for each interval is thrown into a bucket and we apply
whatever math is necessary to extract the desired bit of information from our
input signal. This datum is put into memory and written to the display. This
provides great flexibility. Here we will discuss six different detector types.

In Figure 2-18, each bucket contains data from a span and time frame that is
determined by these equations:

Frequency: bucket width = span/ ( trace points -1)
Time: bucket width = sweep time/ ( trace points -1)

The sampling rates are different for various instruments, but greater accuracy
is obtained from decreasing the span and/or increasing the sweep time
since the number of samples per bucket will increase in either case. Even
in analyzers with digital IFs, sample rates and interpolation behaviors are
designed to be the equivalent of continuous-time processing.

Figure 2-18. Each of the 101 trace points (buckets) covers a
1 MHz frequency span and a 0.1 millisecond time span