MFJ MFJ-201 User manual

ITF]
1.5-250
MHz
DIP
METER
Model
MFJ-201
Operation
Manual

GENERAL |
This
unit
is
a
transistorized:dip
meter
for
rapidly
checking
circuits
and
components
in
receivers,
transmitters,
antennas,
etc.;
in:
the
1.5
to
250MHz
range.
It
is
designed
for
many
applications
in
Amateur
Radio
stations
and-service:shops.
2.
SPECIFICATIONS
‘
Frequency
Range
2
1.5
to
250MHz
with
six
plugin
coils:
Band Range
A 1.5-— 4MHz
B 3.3- 8MHz
c 6.8— 18MHz
D 18— 47MHz
E 45 — 110MHz
F 100 — 250MHz
Modulation
:
Approx.
2kHz;
sine
wave
Crystal
Oscillator
:
1-15MHz,
crystal
in
FT-243
holder
Power
Supply
:
Q
volt
battery
Current
Consumption
:
2mA,
maximum
Semiconductor
Complement
:
2
transistors
and
1
diode

3.
PANEL
CONTROLS
Frequency
dial
:
Six
frequency
scales
calibrate
according
to
bands
and
color of the coil in use.
Meter
:
For
indicating
resonance
and
for
battery
check.
Function
switch
:
Three
positions
OSC:
For
use
as
a
dip
meter
or
absorption
wave-
meter.
MOD : Applies 2kHz AM to the carrier output.
BATT
:
For
checking
condition
of
CHECK
internal
battery.
SENSITIVITY
:
Adjusts
the
output
level
of
the
oscillator;
at
OFF,
the
power
supply
is
cut
off
and
the
instrument
can
be
used
as an absorption
wavemeter.
Earphone
jack
:
For
monitoring
AM
signals
with
a
crystal
earphone
(not
supplied).
4. CIRCUIT DESCRIPTION
The
RF
oscillator
is
a
Colpitts
type
using
a
silicon
transistor.
The
RF
voltage
is
rectified
with
a
diode
and
the
current
is
indicated
on
the
meter.
When
the
dip
meter
frequency
is
in
resonance
with
the
external
circuit,
the
meter
pointer
will
dip.
The
strength
of
the
oscillator
output
is
controlled
2

with
the
SENSITIVITY
adjuster.
When
required,
amplitude
modulation
can
be
applied
to
the
RF
oscillator
output.
A
twin-
T
type
circuit
is
used
for
the
2kHz
source.
In
the
absorption
wavemeter
function,
the
RF
oscillator
Power
is
cut
off
and
the
tuned
and
diode-meter
circuits
are
used.
5.
PRECAUTIONS
IN
OPERATION
1.
During
standby
periods
or
when
the
dip
meter
is
not
in
use,
set
SENSITIVITY
adjuster
at
OFF
(clicked).
This
will
Prolong
battery
life.
Handle
the
coils
carefully
when
inserting
or
removing
same
from
the
socket.
During
measurements,
the
coil
should
be
loosely
coupled
to
the
test
circuit.
The
coupling
must
be
as
loose
as
possible
to
obtain
proper
meter
indication.
Close
coupling
will
in-
troduce
errors
in
measurement.
IMPORTANT!
When
checking
transmitting
equipment,
close
coupling
will
damage
the
diode
detector
by
overload.
Disconnect
the
battery
from
the
internal
circuit
when
the
dip
meter
is
not
in
use
for
long
periods.

6.
OPERATION
1.
Battery
Check
and
Replacement
1.
2.
3.
Set
FUNCTION
at
BATT
CHECK.
Advance
SENSITIVITY
to
power
a.
on.
The
meter
pointer
should
swing
to
the
BATT
OK
portion
on
the
scale.
If
not,
renew
the
battery.
NOTE:
To
install
or
replace the
battery,
remove
the
covers
as
follows:
Remove
the
two
screws
each
at
the
right
and
left
sides
of
the
instrument;
take
off
the
covers.
Loosen
the
battery
clamp
screw
at
center
of
the
chassis
and
take
out
the
battery.
Remove
the
snap
terminals
from
the
battery.
To
install;
reverse
steps.
Tighten
the
clamp
screw
and
put
on
the
side
covers.
After
this
check,
set
SENSITIVITY
at
OFF.
2.
Use
as
a
Dip
Meter
1.
2.
3.
Plug
the
coil
for
the
band
in
use
in
the
socket.
Set
FUNCTION
at
OSC.
Advance
SENSITIVITY
past
the
click
point
so
that
the
meter
pointer
swings
to
about
0.8.
NOTE:
When
the
“F”
coil
is
used,
there
will
be
some
variation
in
the
meter
deflection
as
the
frequency
dial
is
rotated.
This
effect
will
be
present
when
the
coil
is
not
coupled
to
the
test
circuit.
Care
must
be
taken
during
use
not
to
confuse
this
condition
with
the
actual
dip
caused
by
the
test
circuit.
4

|
4.
Couple
the
coil
loosely
to
the
test
circuit
and
rotate
the
frequency
dial
in
small
steps
until
a
dip
is
observed
on
the
meter.
(When
there
are
two
dips
close
together,
place
the
coil
farther
from
the
test
circuit.)
Adjust
the
frequency
dial
until
the
maximum
dip
is
obtained.
Note
the
frequency
on
the
frequency
dial.
Set
SENSITIVITY
at
OFF
after
the
tests.
.
Examples
of
typical
coupling
methods
are
shown
in
Fig.
1.
NOTE:
It
is
important
that
the
power,
if
applied,
to
the
test
circuit
is
turned
off,
aby
4
see
enon
Fig.
—1
Dip
meter
coupling
methods.
5

AandB_:
Director
or
link
types.
C_
:
For
shielded
circuits;
the
coupling
capacitor
should
be
as
small
as
possible.
D_:
Determination
of
resonant
frequency
of
an
antenna;
use
a
1-turn
coil
in
the
antenna.
(For
vertically
grounded
antennas,
do
not
forget
to
make
the
ground
connection.)
E
=
Determination
of
electrical
length
of
quarer-wave
and
half-wave
coaxial
feeders.
3.
Use
as
an
Absorption
Wavemeter
1.
2.
3.
4,
When
the
coil
is
coupled
to
the
coil
in
an
oscillator,
or
RF
tank
coil
in
a
transmitter,
the
Plug
the
coil
for
the
band
in
use
in
the
socket.
Set
SENSITIVITY
at
OFF.
Set
FUNCTION
at
OSC.
meter
pointer
will
swing
upward
when
tuned
to
resonance.
The
amount
of
the
swing
depends
on
the
strength
of
the
oscillations
and/or
coupling
distance.
NOTE:
In
checking
transmitters,
take
care
that
the
energy
picked
up
will
not
overload
the
instrument,
otherwise
the
diode
detector
will
be
damaged.
Further,
do
not
touch
any
of
the
high
voltage
points
within
the
transmitter;
safety
is
important.
Read
the
frequency.
Typical
application
are
shown
in
Fig.
2.

Fig.
—2
Absorption
wafemeter
applications.
Measurement
of
oscillator
frequency.
Measurement
of
frequency
at
the
transmitter
output.
To
check
for
harmonics
or
parasitics,
slowly
rotate
the
frequency
dial
for
the
indications;
change
the
coils
are
necessary.
The
meter
deflection
will
indicate
the
relative
strength
of
these
signals.
Neutralizing
adjustments
can
be
made
by
first
cutting
off
DC
supply
to
the
plate
and
screen
grid
circuits.
The
tank
circuit
is
then
tuned
for
maximum
indication.
Next
the
neutralizing
capacitor,
CN,
is
adjusted
for
minimum
indication.
7

D: Use as a field strength meter is shown. A short antenna is coupled to the coil for signal
pickup.
When
the
wavemeter
is
tuned
to
the
operating
frequency
and
at
different
positions
around
the
antenna,
the
relative
field
strength
will
be
indicated
on
the
meter.
4, Short Wave Receiver Testing
In
this
application,
the
dip
meter
is
used
as
a
simple
test
oscillator,
with
or
without
amplitude
modulation.
The
test
frequency
is
set
with
the
suitable
coil
and
frequency
dial.
The
dip
meter
is
placed
near
the
receiver;
the
“input
signal
strength”
can
be
varied
with
the
distance
between
the
dip
meter and the receiver.
For operation, set SENSITIVITY for RF output.
Communications
receivers
with
best
oscillators
can
be
tested
by
setting
FUNCTION
at
OSC
for the CW signal.
When
an
AM
signal
is
required,
set
FUNCTION
at
MOD.
A
tone
of
approximately
2kHz
will be heard in the loudspeaker.
Adjustments,
as
required,
can
be
made,
with
the
respective
signals,
in
the
receiver
circuits,
5. Monitoring Phone Signals
The
wavemeter
application,
see
Sect.
5.3,
can
be
used
for
monitoring
AM
phone
signals.
A
crystal
earphone
is
connected
to
the
earphone
plug
and
the
plug
is
inserted
in
the
PHONE
jack.
Tune
to
the
RF
test
frequency
using
the
proper
coil.
8

For
“remote”
indication
of
the
modulated
output,
the
meter
can
be
connected
to
the
ear-
phone
plug;
the
inner
contact
is
the
+
side.
.
Use
as
a
Crystal
Oscillator
In
place
of
the
coil,
a
quartz
crystal,
1
—
15Mhz,
in
the
FT-243
holder,
inserted
in
the
socket
will
produce
output
at
the
crystal
frequency.
Set
FUNCTION
at
OSC
and
SENSITIVITY
as
required
for
the
output.
The
frequency
dial
is
rotated
until
the
most
stable
condition
is
obtained.
Set
the
dip
meter
near
the
receiver
for
signal
pickup.
For
modulated
output,
set
FUNCTION
at
MOD.
. Audio
Signal
Output
Set
up
the
instrument
for
dip
meter
operation,
see
Sect.
2,
with
coil
E
or
F
in
the
socket
(However,
the
RF
is not
used.)
Set
FUNCTION
at
MOD.
Audio
output
at
approximately
2kHz
is
available
at
the
PHONE
jack.
The
plug
connections
are
as
follows:
Inner
contact
for
the
“hot”
side
and
the
sleeve
for
ground.
This
signal
can
be
used
for
checking
audio
circuits.
.
Inductance
and
Capacitance
Measurements
Unknown
inductances
and
capacitances
can
be
determined
with
use
of
the
dip
meter,
see
9

Sect.
5—2
and
“A”
in
Fig.
1.
A;
Inductance
measurement:
A
capacitor
of
known
value
is
required.
This
capacitor
is
connected
in
parallel
with
the
unknown
coil
and
the
resonant
frequency
is
noted.
The
inductance
is
calculated
from
the
following:
L=
pwH
CoF
(fMHz)22
With
use
of
a
standard
100pF
capacitor,
the
measureable
inductance
range
is
from
113yH
to
0.004yH
with
use
of
the
frequency
range
in
the
dip
meter.
B:
Capacitance
measurement:
An
inductance
of
known
value
is
connected
in
parallel
with
the
unknown
capaci-
tor,
and
the
resonant
frequency
is
noted.
The
capacitance
is
calculated
from
the
following:
25,330
ee)
Cal (fmHz)2
10