Page 46
Figure
2-4
6. Closely couple the Dip Meter coil to the
test
circuit
as shown in
Figure
2-4.
7. Slowly
turn the dial from one extreme toward the other.
As the Dip
Meter tunes
to
the electromagnetic field of the test coil,
the
meter
will quickly rise
to
a peak indication.
8. Very carefully
turn the tuning dial
back and forth
to
obtain
the
highest meter
reading while
you
slowly
pull the Dip Meter
away
from the test
coil.
9. Read the
frequency, in MHz, of
the test circuit directly from the
scale whose color is the same as that of the chosen coil.
Absorption
Mode Theory
In the absorption mode of
operation, the
Dip Meter detects the
presence of
external RF energy.
Test circuit
L
t
—
C
t
in Figure
2-5
is energized and
inductively
couples its energy
to
the Dip
Meter pickup coil.
As
the
Dip Meter is
tuned
to
this frequency,
a
circulating
current develops in the
Dip Meter tank
circuit.
Regeneration within the
oscillator circuit is insufficient
for oscillation,
but acts as a Q-multiplier and increases
the selectivity of
the RF detector. This
external
energy is then indicated
on the meter
as a peak at the resonant
frequency.
HD-1250
HEADPHONES
In dip meter applications, headphones are
not
frequently
used. In
some
situations, however, they
may be
helpful. When
the Dip Meter is used with the
headphones, and the
tuning dial is moved across a point of resonance, usually
the indication
will be a clicking sound in the phones. There is an exception.
When
an RF circuit
is
modulated with an audio signal, this audio will be
reproduced in the headphones, providing it
is
of sufficient
amplitude.
LOG SCALE
A log, or general reference, scale is included on the inner ring of your dip meter
dial. If you wish to make additional plug-in coils, you may use this
0
to 17
uncolored scale
to
correlate frequency-to-dial readings.
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