C Om M On-M Ode Rejection; Amplitude Comparison (Ratio) - Tektronix 2205 Operator's Manual

Applications

C om m on-M ode Rejection

The following procedure shows how to eliminate unwanted AC
line frequency components. Similar methods could be used to
eliminate other unwanted frequency components or to provide a
DC offset.
1. Apply the signal containing the unwanted line-frequency
components to the CHI input connector.
2. Apply a line-frequency signal to the CH2 input connector. To
maximize cancellation, the signal applied to Channel 2 must
be in phase with the unwanted line frequency component of
the Channel 1 input.
3. Set the three VERTICAL MODE selectors to BOTH-NORM-
ALT; set both VOLTS/DIV controls equally to produce dis­
plays of approximately four or five divisions amplitude.
4. Adjust the CH2 VOLTS/DIV and Variable (CAL) controls so
that the Channel 2 display is approximately the same ampli­
tude as the undesired portion of the Channel 1 display (see
Figure 3 -3 top).
5. Now set the middle and right VERTICAL MODE selectors to
CH2 INVERT and ADD. Slightly readjust the CH2 VOLTS/DIV
variable control for maximum cancellation of the undesired
signal component (Figure 3 -3 bottom).

Amplitude Comparison (Ratio)

In some applications, it may be necessary to establish a set of
deflection factors between step settings of the VOLTS/DIV con­
trols. This is useful for comparing unknown signals to a refer­
ence signal of known amplitude.
To accomplish this, a reference signal of known amplitude is first
set to an exact number of vertical divisions by adjusting the
VOLTS/DIV and VOLTS/DIV Variable (CAL) controls.
signals can then be quickly and accurately compared to the ref­
erence signal without disturbing the setting of the VOLTS/DIV
Variable controls.
1. Apply the reference signal to either the CHI or the CH2 input
connector and set the left VERTICAL MODE selector to dis­
play the channel used.
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2205 Operator's