Fig. 2-23. Frequency difference measurement
between two signals.
cillator fundamental. If an incorrect dial scale is used to
measure the frequency movement of the signal, as the RF
CENTER FREQUENCY is tuned, an erroneous reading will
be obtained, This erroneous reading however can be used
to identify which scale to use to obtain the corect frequency
reading. For example: With a dispersion of 5 MHz/div
(50 MHz total) a given signal moves 50 MHz for a RF CEN-
TER FREQUENCY change of 25 MHz. This indicates the
signal is mixing with the next higher harmonic of the os-
cillator, and the next higher scale should be used to read
the signal frequency. If the signal only moves 25 MHz for
an RF CENTER FREQUENCY change of 50 MHz, the next
lower scale should be used.
6. The rate at which the signal moves across the disper-
sion window as the RF CENTER FREQUENCY is tuned also
aids in identifying which scale to use, and with practice,
the correlation of the signal rate of movement and the dial
scale becomes fairly easy.
Spurious responses due to intermodulation are the most
difficult to identify. Signal characteristics, such as type and
amount of modulation, irregular spacing between signals,
etc., are the main character identities.
The spectrum analyzer is a very versatile device in the field
of radiation measurements. It can be used for example, as
an aid in the design and adjustment of transmitters, to check
and calibrate oscillators, check and calibrate attenuators, or
as a sensitive detector device to study all types of modu-
lated signals, plus many more special applications.
Fig. 2-22. Pulse shaping effects
on the pulse spectrum.