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Figure 39-9. The Spectrum analyser
The notch (bandstop) curve can be seen on the display. The centre frequency to
which the notch is tuned can be seen in the middle of the display, which is
145MHz. If the notch was off frequency, we would just have to adjust the
tuning rods while looking at the display to move the curve to the centre.

We know the maximum depth of the notch from the reference level of 0dBm.
The graticule is calibrated in 10dB divisions, though this can be changed with
the controls. The insertion loss outside the notch can be read directly off the
display.

Using a spectrum analyser with an inbuilt tracking generator is the best way to
tune cavity filters, diplexers, isolators and any other frequency tunable device.
This has by no means been an exhaustive treatment of oscilloscopes and
spectrum analysers. To do so would be a book in itself. Many radio clubs have
test equipment for use by the members, though they will probably want to
know that you can safely use it before loaning it out. Some measurements, like
the latter, are very safe. It is impossible to damage the equipment, but when
performing transmitter measurements, we must take great care not to exceed
the test instrument's maximum input power. Excessive power, even for a
fraction of a second, can do expensive damage to test equipment. The best
way to learn is to use the test equipment and ask for guidance if needed.
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