L3Harris narda PMM EP-600 User Manual page 39

3.1 Foreword
3.2 Preliminary
3.2.1 Spurious signals
1
Document EP60XEN-01122-3.16 – © NARDA 2020
3 – Measurements
The following procedures and measurement methods
electromagnetic field sources present in industrial, medical, research,
residential and telecommunication applications..
Before starting measuring electromagnetic fields (EMF) potentially
dangerous, it's advisable to determine the known characteristics of the
sources and their possible propagation characteristics.
This will allow for a better evaluation of the field distribution and for
selecting the correct measuring equipments and procedures.
The source characteristics may include:
- type of generator and radiated power
- carrier frequency or frequencies (i)
- modulation
- polarization of transmitting antenna
- duty cycle, width and repetition frequency for pulsed modulations
- type of antenna and characteristics (gain, size, radiation diagram etc.)
- the number of sources, including those out of the probe bandwidth
To know for propagation evaluation:
- distance between source and point of measurement
- presence of RF absorbing or reflecting structures that may influence the
field intensity.
The operation with diode-based field sensors does require considering
possible effects due to spurious signals, like:
- Multiple sources. Diodes feature RMS response only for low level
signals. In presence of two or more strong signals the probe readings are
higher than the real RMS value of the field in the corresponding bandwidth.
- Pulse modulation. At high levels the diode response is linear.
Consequently, in presence of pulsed signals of low duty cycle the probe
tends to read values higher than the real average value. This must be
particularly considered for radar signals.
- Sensitivity to light. The Schottky diodes employed in some field probes
are sensitive to light, including infrared. In such cases it's advisable to avoid
direct exposition to the light sources.
- Perturbing structures . Metallic and in general conductive surfaces and
structures can influence the field probe readings. Field probes must be
operated at a proper distance from such structures.
Measurements
apply to
3-1