RCA 54-45 Manual page 29

LISSAJOUS PATTERNS: Another type of fundamental pattern is obtained when both the vertical
and horizontal deflection voltages are sinewaves that are related in frequency as follows : one frequency
is a whole number of times larger than the other; one frequency is a simple fraction of the other .
When one or the other of these conditions is fulfilled, stationary closed-loop patterns are obtained.
These patterns are called Lissajous figures after the 19th century French scientist. They are parti­
cularly useful in determining the frequency ratio between two sinewave signals .
one signal is known, the frequency of the other signal can be easily determined from the frequency
ratio. Usually the known signal is applied to the horizontal channel and the unknown signal to the
vertical channel. The shape of the pattern changes with the phase relationship between the known and
unknown signals. For example, all the patterns shown in Fig. 3 (and those intermediate) are possible
with a frequency ratio of 1 : 1 if the phase differences indicated exist.
In general, to determine frequency ratio from the Lissajous figure, count the number of points of
tangency to horizontal and vertical lines , drawn or imagined (see Fig. 4). Points of tangency at the
top of the figures result from the unknown frequency applied to the vertical channel.
side of the figure result from the known frequency applied to the horizontal axis . As a matter of fact,
the following relationship holds true in all cases :
V axis freq
H axis freq
As an example, take Fig. 4c, which shows' four points of tangency at the top and one point at the
side . This indicates that the unknown frequency applied to the vertical axis is four times the known
frequency. In Fig. 4f, one point of tangency at the top and four at the side indicate that the unknown
frequency is one-fourth the known frequency.
An Audio Generator (or Electronic Switch) having a square wave output can be used to check ampli­
fiers as to frequency response, phase shift, transient response, deficient design, or faulty components.
The equipment is set up as shown in Fig. 5 .
I 0 0 \J \
Figure 3. 1: 1 Ratio of Lissajous Patterns
2 : 1 3 : 1
00\maiDS§�
A
I
Figure 4. Lissajous Patterns
V pts of tangency
=
H pts of tangency
4 : 1 1 : 2 1 : 3
c
D
28
If the frequency of
1800
1 : 4
Those at the