Manual FCKL 1528 page - 20
12.2 Meter and Scaling
12.2.1 Zeroing
12.2.1.1 Mechanic zeroing of the meter: The indicator (pointer) is adjusted to the N -
point on the left side of the meter scaling by turning the screw below the meter window.
12.2.1.2 Electric zeroing:
Even when no signal is coming into receiver (coaxial cable
disconnected), there are small „idle“ measurements on the meter.
They are caused by the internal noise of the receiver and are different for different
receiver settings. These noise reading is absolutely correct and no error.
Any method to avoid this basic noise would affect the measurement of small signals.
In order to prevent misreading caused by noise in the very common case of CISPR
Quasi-Peak-Detector, Low distortion and Band B (150 kHz-30 MHz), there is a note on
both linear and logarithmic scale.
The noise reading depends on:
A) Linear and logarithmic scale: The logarithmic scale can show smaller signals than the
linear one. This means that also the small „Noise Signal“ shows more indicator angle on
the left side of the scale.
B) Low distortion) / Low noise): Low distortion shows approx. 20 dB more noise than Low
noise. Low noise gives a longer usable scale with the disadvantage of potential (non
damage) receiver overload.
C) The frequency ranges Band A (9 Hz-150 Hz) and Band B (150 Hz-30 MHz) use
different bandwidths and detector time constants. As a consequence the noise indication
in Band A is much lower than in Band B.
D) The 3 different detectors differently convert receiver noise into noise reading. The
Peak/Mil-detector shows the highest reading, followed by CISPR Quasi-Peak and
Average.
