Heathkit IG-18 User Manual

Page 54
HORIZONTAL
TANGENT LINE
A
VERTICAL
TANGENT-i---i
1I NE
C
UNKNOWN FREQUENCY EQUALS
KNOWN FREQUENCY
UNKNOWN FREQUENCY EQUALS
1/2 KNOWN FREQUENCY
UNKNOWN FREQUENCY EQUAL
2x KNOWN FREQUENCY
D
UNKNOWN FREQUENCY EQUALS
3x KNOWN FREQUENCY
Figure 10
To measure an unknown frequency, adjust the
Generator frequency until the pattern com es as
close as you can adjust it to the circle shown in
Part A of Figure 10. This circle may appear
to revolve in such a way that it alternately
assumes each of the following forms: a slanting
line to the left, an ellipse, a circle, an ellipse,
again, a slanting line to the right, an ellipse,
etc. Often, it will be almost impossible to keep
the circle from revolving.
When the circle is displayed on the oscilloscope
screen, the frequency of the unknown signal is
then exactly equal to the frequency of the Genera-
tor, as shown on the Generator dial. The accura-
cy of the measurement is the same as the accu-
racy of the Generator frequency.
Unknown frequencies that are beyond the fre-
quency limits of the Generator can be measured
by USing more complex Lissajous patterns, such
as the ones shown in Parts B, C, D, and E of
Figure 10. In these cases, the pattern shown on
the oscilloscope gives the ratio between the
frequency of the Generator Signal and the fre-
quency of the unknown signal. Determining the
frequency of the unknown Signal then becomes
a matter of simple arithmetic. The frequency
of the unknown signal can be calculated using
the following formula:
Th X F
Unknown
Frequency =
Tv
In the above formula, This the number of loops
that touch the horizontal tangent line; F is the
Generator frequency; and T v is the number of
loops which touch the vertical tangent line.

Heathkit IG-18 Specifications

General

Brand	Heathkit
Model	IG-18
Category	Test Equipment
Language	English