13
passive probes. The 3M
™
ScanEM-C
Electromagnetic Near Field Probes
have broad and flat frequency
responses within a specified range
(see page 13 for details). The
ScanEM-C Probe’s built-in amplifiers
provide ~20 dB of gain, virtually
eliminating the need for an external
amplifier.
Figure C shows a typical frequency
response of the ScanEM-EC Probe
vs. an equivalent passive probe. As
seen, passive probes typically fail at
lower frequencies (below 200 MHz),
where most of the fundamental
frequencies and many of the strongest
harmonics of the tested equipment
are located. Figure D shows
comparative frequency responses of
the 3M
™
ScanEM-HC Probe and its
passive counterpart at lower frequencies.
Avoid overloading the probes with a very strong field—it may induce
distortions in the ScanEM-C Probe amplifiers. The ScanEM-EC Probe, for
example, begins to overload at field strengths of approximately 4 V/m.
Non-Contact Oscilloscope Probes
When connected to an oscilloscope, the ScanEM-C Probe becomes an
extremely broadband non-contact probe, which is a great diagnostics and
troubleshooting tool. The typical challenge for oscilloscope measurements
-5
-15
-25
-35
-45
-55
-65
-75
-85
-5
-15
-25
-35
-45
-55
-65
-75
-85
Passive Probe
Passive Probe
O MHz
1000 MHz
VBW 10 kHz
RBW 10 k
Attn 0 dB
O MHz
1000 MHz
VBW 10 kHz
RBW 10 k
Attn 0 dB
ScanEM EC
ScanEM EC
Figure C: Typical Frequency Response of 3M
™
ScanEm-EC Probe vs. Passive Probe
Figure D: Typical 3M
™
ScanEM-HC Probe
Frequency Response vs. Equivalent Passive Probe
(Lower Frequency Range)
