To Find The Inductive Of Rf Coils; To Find The Inductive Of Toroid Coils; To Check For Parasitic Oscillations - Heathkit HD-1250 Manual

TO
FIND
THE INDUCTANCE OF
RF COILS
1.
Connect
a
low
value capacitor across the
unknown
inductor; for example
100
pF.
2.
Use
the
Dip
Meter
in
the
injection
mode.
3.
By
trial
and
error, find
a coil
that
will
dip
on
the resonant frequency of
the
parallel circuit.
Record
the frequency.
4.
Compute
the inductance of the
coil
with the following formula:
1
39.48
xfxC
1
nH =
10"
6
henries
1
mH
=
1fJ
3
henries
TO
FIND
THE INDUCTANCE OF TOROID
COILS
The
previous
steps
cannot be
applied to
toroid coils
because they have
self-shielding properties.
However,
these
coil
values
may
be determined
in
the
following manner:
1
.
Use the Dip Meter
in
the
injection
mode.
2.
Connect the extension probe
to
several
loops of wire
wound
around
the
core of the
coil.
A
magnetic
flux will be picked
up
in
the
special-wound
link
and
coupled
to
the Dip
Meter.
See
Figure 3-4.
3.
Compute
the
unknown
inductance
as in
the
previous
section.
TO CHECK FOR
PARASITIC OSCILLATIONS
1.
Apply power
to the transmitter.
2.
Use the Dip Meter
in
the absorption
mode.
3.
Carefully check
transmitter
stages for undesired frequencies.
4.
Once
a parasitic oscillation has
been
located, turn off transmitter
power.
5.
Use
the
Dip Meter
in
the
injection
mode. Check
the areas of the
transmitter near the
point the
first
resonance was
detected,
at
or near the
original
frequency. Check
circuit
wiring,
RF
chokes,
circuit
grounds,
and
other
potential resonant
circuits.