Tektronix Type 82 PLUG-IN Instruction Manual page 10

nect a resistor of about 100 to 1000 ohms in series with the
lead where it connects to the input connector of the Type 82.
A fourth method is to use the P6008 Probe.
(6) Oscillations that arise from using coaxial (shielded) leads
can be eliminated in a manner similar to that described for
unshielded leads. That is, add a suitable value resisto: in
series with the center conductor of the cable near the input
to the Type 82, use some other setting of the V/CM switch,
or use the P6008 Probe.
(7) In high-frequency applications, it will be necessary to
terminate the coaxial cable with a resistor or an attenuator
presenting a resistance equal to the characteristic impedance
of the cable. This will not only prevent the resonance effects
but also prevent ringing (high-frequency damped oscillations).
(8) It becomes more necessary to terminate the cable piop-
erly as the length of the cable increases. The termination is
generally placed at the oscilloscope end of the cable, al-
though many sources require an additional termination at the
source end of the cable as well.
(9) If you are working with 50-ohm systems, you may need! to
use the vswr versus frequency curve shown in Fig. 2-3. The
curve was obtained using a signal source which was te: mi-
nated into 50 ohms at the input of the Type 82. The te:mi-
nation which was used is a type that has BNC connectors on
Operating Instructions—Type 82
each end (Tektronix part number 011-049). If a 50-ohm 10:1
T attenuator (Tektronix part number 010-314) is connected
between the signal source and the termination, the vswr will
be the same as the vswr of the 10:1 attenuator.
(10) Applies only to units below SN 3000. In fast-rise pulse
application where a step function with a risetime of 10
nanoseconds or less is applied to the Type 82, clean re-
production of the step function can be obtained (limited only
by the risetime of the system) for all except the three highest
positions of the V/CM switches. The three highest positions
are: 5 (.5), 10 {1} and 20 (2). In these positions aberrations
occur on the rising portion and leading corner of the wave-
(11) Applies only to units below SN 3000. If the fast-rise step
function of 10 nanoseconds or less is applied through a Type
P6008 Probe to the input of the Type 82, the aberrations
will still occur because the probe is capable of coupling the
signal to the Type 82 with very little loss in risetime. If it is
important to take full advantage of the faster risetime and
transient response of the Type 82/Type 580-Series oscillo-
scope combination, use the lower positions of the V/CM
switches and external attenuation. For example, Tektronix
BNC 50-ohm attenuators provide proper external attenuation
without sacrificing transient response when used with 50-
1.8
1.4
1.2 L
1 2 4 6 8 10 20 40 60 80 100
FREQUENCY IN MEGACYCLES PER SECOND
Fig. 2-3. Typical vswr versus frequency curve measured at the Type 82 input connector. The signal source was terminated into 50 ohms
at the connector.
2-3