Vertical Axis - Deepace KC908 Manual

3.1.2 Vertical Axis

In spectrum mode, amplitude can refer to power, voltage or current. A
spectrum analyzer is a load-bearing instrument that measures the power
flowing into its port, or the voltage and current on the port. These parameters
are obviously load related. According to Ohm's Law, if the resistance of the
load (which can be generalized to impedance) is determined, then the power,
voltage, and current on the load are interdependent, and by measuring one,
one can know the other two.The nominal impedance of the KC908 is 50 Ω, so
whether the power, voltage, or current is displayed, the amplitude of the
signal is correctly represented. In RF measurements, power is often used,
occasionally voltage, and rarely current. the KC908 displays the signal power
by default.
The unit of power is watts (W), which is a linear unit. In RF measurements,
the amplitude of the signal is very different from each other, perhaps a signal
is only 1nW, while the signal next to it has 1mW, a difference of 1 million
times. If a linear scale is used for the vertical coordinates, assuming you want
to represent a 1nW signal with a 1mm height, then a 1mW signal is 1
kilometer high, and there is no such large display in the world. Therefore,
amplitude is usually converted to logarithmic units.
The vertical coordinates of the KC908 default to a logarithmic scale.
Logarithms are proportional relationships. For power, 60dB means 10^6 times,
or 1 million times. Since it is a ratio, there is the question of who the