Tektronix TYPE 109 Instruction Manual page 11

one end of the cable is connected to the 500 CH G. LINE
1 connector and the other end of the cable is connected to
the 500 CH G . LINE 2 connector. Since the same cable is
used to generate both pulses of a pair, all pulses have
exactly the same duration and amplitude. This mode of
operation results in an opposite polarity pip at the center
of the pulse, due to capacitive coupling between the switch
contacts of SW750. The pulse Ifength will be twice the
delay time of the charge line plus one nanosecond.
When using the same charge line between connectors,
maximum pulse duration at full amplitude is limited by
the amount of time that the reed of the mercury switch
remains between contacts. This is the open-contact time.
To assure that the charge line has sufficient time to fully
charge during this time, the length of the charge line should
not exceed 50 nanoseconds. Therefore, to generate pulses at
their full amplitude, maximum pulse duration is limited to
about 100 nanoseconds. If longer duration pulses are gener­
ated by using a longer charge line, the pulses may not
reach full amplitude. In addition, each pair of pulses gen­
erated may not equal each other in amplitude due to
variations in open-contact times.
To generate longer pulses at full repetition rate, two
separate charge lines can be used. As an alternate method,
a single unterminated charge line can be used if you
disable the other line-charging network. To disable the
network, ground the unused 50Q CH G. LINE connector or
disconnect either R751 or R756. If the alternate method is
used, the repetition rate of the pulses will be one-half the
original rate. By using either of these methods, pulse dura­
tions up to 300 nanoseconds can be satisfactorily obtained.
2. Using the C h a rg e Netw ork Accessory
Included with your Type 109 is a special Charge Network
designed to produce a fast-rise pulse that decays one RC
in about 5 microseconds. The amplitude decay is only 10%
in 400 nanoseconds (see Fig. 1-5, Characteristics section).
The Charge Network plugs into the 50Q C H G . LINE 2 con­
nector and the banana plug goes into the center conductor
of the 50Q CH G . LINE 1 connector. The banana plug dis­
ables or grounds the unused contact of the mercury switch.
Since one set of contacts are used to generate the pulse,
the repetition rate is one-half the normal rate. The output
amplitude of the pulse is about one-tenth that indicated by
the VO LTAG E RAN GE and AMPLITUDE controls.
Maximum allowable external voltage that can be applied
to the Charge Network is 50 volts.
Selecting the Pulse Amplitude
1. Using the Type 109 Power Sup ply
In most applications the coaxial lines which are used to
generate the output pulses are charged by the internal
100-volt power supply of the Type 109. In these applica­
Operating Instructions— Type 109
tions, the pulse amplitude is controlled by the VO LTAGE
RANGE and AMPLITUDE controls. The VO LTAGE RANGE
control determines the range of adjustment of the AMPLI­
TUDE control. The scale of the AMPLITUDE control, when
used with the setting of the VO LTAG E RANGE control,
indicates the approximate
internal power supply, pulses with amplitudes between zero
and 50 volts can be produced.
Alternate pulses of different amplitudes can be produced
using the Type 109 internal voltage supply and separate
charge lines. To do this, connect a rheostat across either
of the EXT. POWER OR M ONITOR connectors. If this is
done, however, the front-panel amplitude settings will not
be correct, due to the external loading.
2. Using an External Power Source
Pulses with amplitudes higher than 50 volts can be gen­
erated if an external power source is used to charge the
coaxial lines. To use an external power source, first place
the VO LTAG E RANGE control in the EXT. PWR. position.
Then connect the external power source or sources to the
EXT. POWER or M ONITOR connectors on the front panel.
The pulse amplitude obtained will be approximately one-
half the power source voltage, up to approximately 100
volts. At some higher voltage, the relay will suddenly
develop a higher arc drop resulting in a reflection at the
relay. This reflection will cause the output to be less than
one-half the power source. The voltage applied to the Type
109 to charge the lines should be limited to approximately
600 volts using one or both contacts to prevent damage to
the 47-k 2-watt limiting resistors, R752 and R757.
An additional advantage in using external power to
charge the coaxial lines is that alternate pulses of differ­
ent amplitudes and/or polarity can be generated by using
two different power sources. This can be combined with dif­
ferent length charge lines to produce not only different
amplitudes but different pulse widths as well.
Selecting the Pulse Polarity
The PULSE POLARITY switch controls the output polarity
of the pulses when internal power is used to charge the
coaxial lines. The polarity of the output pulses is the same
as the polarity of the charge voltage.
When external charge power is used, alternate positive
and negative pulses can be obtained by charging one
line with a positive source and the other line with a nega­
tive source. If identical pulse widths are required for both
the positive and negative pulses, it will be necessary to
select identical charge cables.
connected between the 50Q CHG. LINE 1 and 50L2 CHG.
LINE 2 connectors should not be used for this mode of
operation because the cable cannot be charged simultan­
eously by both a positive and a negative voltage.)
pulse amplitude. Using the
(A single charge cable
2-3