2635 manual - BK Precision

Types of Spectrum Analyzers
graphically displays voltage or power as a function of frequency
on a CRT (cathode ray tube).
In the time domain, all frequency components of a signal are
seen summed together. In the frequency domain, complex signals
(i.e. signals composed of more than one frequency) are separated
into their frequency components, and the power level at each
frequency is displayed. The frequency domain is a graphical
representation of signal amplitude as a function of frequency.
The frequency domain contains information not found in the time
domain and therefore, the spectrum analyzer has certain
advantages compared with an oscilloscope.
The analyzer is more sensitive to low level distortion than a scope.
Sine waves may look good in the time domain, but in the
frequency domain, harmonic distortion can be seen. The
sensitivity and wide dynamic range of the spectrum analyzer is
useful for measuring low-level modulation. It can be used to
measure AM, FM and pulsed RF. The analyzer can be used to
measure carrier frequency, modulation frequency, modulation level,
and modulation distortion. Frequency conversion devices can be
easily characterized. Such parameters as conversion loss, isolation,
and distortion are readily determined from the display.
The spectrum analyzer can be used to measure long and short
term stability. Parameters such as noise sidebands on an oscillator,
residual FM of a source and frequency drift during warm-up can
be measured using the spectrum analyzer’s calibrated scans. The
swept frequency responses of a filter or amplifier are examples of
swept frequency measurements possible with a spectrum analyzer.
These measurements are simplified by using a tracking generator.
There are two basic types of spectrum analyzers, swept-tuned
and real-time analyzers. The swept-tuned analyzers are tuned by
electrically sweeping them over their frequency range. Therefore,
the frequency components of a spectrum are sampled sequentially
in time. This enables periodic and random signals to be displayed,
but makes it impossible to display transient responses. Real-time
analyzers, on the other hand, simultaneously display the amplitude
of all signals in the frequency range of the analyzer; hence the
name real-time. This preserves the time dependency between
signals which permits phase information to be displayed. Realtime
analyzers are capable of displaying transient responses as
well as periodic and random signals.
30 Subject to change without notice