
2
-1
7
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*
TABLE 2 -1
Signal Transporting Methods, Passive
Method
Advantages
Limitations
Equipment
Required
Source
Loading
Precautions
Unshielded Test Leads
Availability
Limited
frequency
re
sponse; subject to stray
pickup and oscillation
B N C - 1 o - Binding
Post
Adapter; two test leads
Oscilloscope
input
im
pedance
Insert 47 O resistor in se
ries with signal lead to
suppress oscillations. Place
leads strategically to re
duce
shunt
capacitance
and stray pickup
Untermi noted
c o a x i a l
cable or 1 X probe
Convenience
Limited
frequency
re
sponse; high capacitance
of cable
Coaxial cable with BNC
connectors; or 1 X probe
Oscilloscope
input
im
pedance plus cable ca
pacitance
High
capacitive
loading
Coaxial cable terminated
in characteristic impedance
at oscilloscope
F u l l oscilloscope band
width. Provides uniform re
sponse while using long
cables
Loading effect due to
termination (typically 50
Q); power limit of termi
nation
Coaxial cable with BNC
connectors and BNC ter
mination (typically 50 Q)
Termination value (Typ
ically 50 0) in parallel
with oscilloscope input
impedance
Loading
on
test
point;
power limit of termination;
Use DC-blocking capacitor
between source and termi
nation;
reflections
from
oscilloscope input imped
ance
Terminated coaxial cable
with coaxial attenuator be
tween source and termina
tion
Less reflection from oscil
loscope input impedance;
increased voltage range
Reduces oscilloscope sen
sitivity
Coaxial cable with BNC
connectors; BNC coaxial
attenuator; BNC termi
nation
Termination value (typ
ically 50 0) in parallel
with
oscilloscope input
impedance
Loading
on
test
point;
power limit of attenuator
and termination; use DC-
blocking
capacitor
be
tween source and termi
nation
Tap into terminated co
axial system with a BNC
T at oscilloscope input
Optimum signal transfer;
no termination required at
oscilloscope
BNC T; 2* signal cables
with BNC connectors
Oscilloscope
input
im
pedance
Signal size may require
use of attenuators
Attenuator probes
Reduces oscilloscope load
ing; increases v o l t a g e
r a n g e ; protects oscillo
scope
Oscilloscope
sensitivity
reduced by attenuation
factor
1 0 X , 100X or 1000X
probe
1 0 X sr 10 M n and 10
pF
100X
10 MQ and
2.5 pF
1000X ~ 100 M n and
3 pF
Current probe
Permits current evaluation
without interrupting circuit
Current Probe; Amplifier
(optional) increases range
R < 0 .0 3 n
L < 3 f i H
O
p
e
ra
tin
g
In
s
tru
c
tio
n
s
—
T
y
p
e
3
2
4