Application Note

Application Note
Staring at a waveform on an
oscilloscope screen in the hope
of seeing a random glitch occur,
and then trying to manually
freeze the display before the
next waveform update is just
about an impossible task! But
how do you capture random
glitches? With the pass/ fail
testing function found in the
Fluke ScopeMeter 190 Series
II portable oscilloscope, elusive
waveforms are automatically
captured.
We will use the well known
ITU G703 pulse mask template
as an example to illustrate how
easy it is to capture waveform
anomalies that fall outside of
a waveform template that you
create.
Capturing elusive waveform
anomalies with pass/fail
testing function in a Fluke
ScopeMeter
®
190 Series II
portable oscilloscope
From the Fluke Digital Library @ www.fluke.com/library
Figure 1: G703 - E1 template
Figure 2: ISDN30 network
The G.703 standard
The G.703 standard was origi-
nally introduced for voice and
data transmission over digital
networks. It is an ITU recom-
mendation (formerly CCITT)
that’s associated with the PCM
standard. Analog voice to dig-
ital-data conversion according
to PCM requires a bandwidth
of 64 kb/s (±100 ppm), result-
ing in the basic unit for G.703.
Through multiplexing, this
results in a T1 of 1.544 Mb/s
and E1 of 2.048 Mb/s.
The electrical characteristics
of the network interfaces are
described in recommendation
G.703. The signal limits for a
2.048 Mb/s signal are shown in
Figure 1.
ISDN 30
Patch
Panel
Balun SDH
Distr.
2 Mb/s
120 Ω
2 Mb/s
120 Ω
2 Mb/s
75 Ω
Telephone
Exchange
Multiple-channel testing
using two different masks
A balun is used between the
patch panel and a coaxial
transmission line to match the
impedance of the 120 Ω sym-
metrical line to a 75 Ω coaxial
line. The input and output of
the balun each has its specific
mask.