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INTRODUCTION .............................................................................................................. 1
Inductive coupling (Fig. 1A)........................................................................................... 1
Capacitive coupling (Fig. 1B)......................................................................................... 1
FEATURES ........................................................................................................................ 3
SPECIFICATIONS............................................................................................................. 4
CONTROLS ....................................................................................................................... 5
PRECAUTIONS ................................................................................................................. 6
Battery and Oscillation Coil Loading ............................................................................. 6
Obtaining a Dip Point ..................................................................................................... 6
Measuring Transistor Resonant Circuits......................................................................... 6
Caution in Measuring Transmitters ................................................................................ 6
Caution in Motor Pointer Deflection Change ................................................................. 7
APPLICATIONS ................................................................................................................ 7
Use as a Dip Meter.......................................................................................................... 7
Other Frequency Measurements ..................................................................................... 8
Resonant circuit measurement .................................................................................... 8
Use of the capacitive probe......................................................................................... 8
Antenna resonant frequency measurement ............................................................... 10
Use as a Signal Generator ......................................................................................... 11
Use as Crystal Checker and Marker Generator......................................................... 11
Use as an Absorption Frequency Meter.................................................................... 12
Use as a Field-Strength Meter................................................................................... 13
Capacitance and Inductance Measurements ............................................................. 14
ADJUSTMENT ................................................................................................................ 17
VR1: 01 Bias adj........................................................................................................... 17
VR2: Meter zero adj...................................................................................................... 17
VR3: Sensitivity adj...................................................................................................... 17
VR4: Battery voltage check adj. ................................................................................... 17
PARTS AND SERVICE................................................................................................... 17
Ordering Spare Parts ..................................................................................................... 17
Service........................................................................................................................... 17
PARTS LIST..................................................................................................................... 18
PRINTED CIRCUIT BOARDS ....................................................................................... 22
SCHEMATIC DIAGRAM ............................................................................................... 24
DM-81
DIP METER

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   Summary of Contents for Kenwood DM-81

  • Page 1: Table Of Contents

    DM-81 DIP METER INTRODUCTION ......................1 Inductive coupling (Fig. 1A)................... 1 Capacitive coupling (Fig. 1B)..................1 FEATURES ........................3 SPECIFICATIONS......................4 CONTROLS ........................5 PRECAUTIONS ......................... 6 Battery and Oscillation Coil Loading ................6 Obtaining a Dip Point ..................... 6 Measuring Transistor Resonant Circuits.................

  • Page 2

    KENWOOD DM-81...

  • Page 3: Introduction

    Capacitive coupling This is a special feature of the DM-81 which is not found in any other dip meter. The resonant frequency can be checked simply by touching the capacitance probe to the hot side of the resonant circuit under test, instead of coupling the DM-81's coil and measuring inductively.

  • Page 4

    KENWOOD DM-81...

  • Page 5: Features

    6. An FET and transistor are used in the meter circuit to provide extremely good sensitivity. 7. As an absorption frequency meter, your DM-81 is used both to align transmitters and measure field strength. 8. An earphone plug allows you to monitor transmitted signals.

  • Page 6: Specifications

    KENWOOD DM-81 SPECIFICATIONS 700kHz - 250MHz (± 3%) A band 0.7 - 1.6MHz (± 3%) B band 1.5 - 3.6MHz (± 3%) C band 3.0 - 7.4MHz (± 3%) Frequency range: D band 6.9 - 17.5MHz (± 3%) E band 17 - 42MHz (± 3%) F band 41 - 110MHz (±...

  • Page 7: Controls

    KENWOOD DM-81 CONTROLS...

  • Page 8: Precautions

    Replace the battery when weak. After use, be sure to turn the POWER switch off. If your DM-81 will not be used for a long period of time, remove the battery. You can easily remove it by pulling the take-out ribbon toward you.

  • Page 9: Caution In Motor Pointer Deflection Change

    KENWOOD DM-81 Caution in Motor Pointer Deflection Change The meter pointer may swing slightly as if indicating a dip, This results from a variation in oscillation signal strength while tuning the oscillator variable capacitor. Move the dip meter coil away from the circuit under measurement. The meter pointer will return to full scale for a real dip.

  • Page 10: Other Frequency Measurements

    Other Frequency Measurements Resonant circuit measurement A basic measurement with your DM-81 is a frequency check of resonant (tuned) circuits comprised of coils and capacitors. In practice, the dip meter is brought near the coil to be measured as shown in Figure 1A. This illustrates a standard method of resonant frequency measurement.

  • Page 11

    KENWOOD DM-81 The dip point can be obtained by using the ground clip and probe for frequencies of about 50MHz or lower, and the probe only for about 5OMHz and higher. Toroidal coils can be measured in the same manner. Note that the probe should be connected to the hot side (not the ground side) of the circuit.

  • Page 12: Antenna Resonant Frequency Measurement

    KENWOOD DM-81 Antenna resonant frequency measurement Any antenna can be regarded as a kind of resonant circuit. Its resonant frequency, therefore, can be measured as illustrated in Figure 5. For measurement, connect a one-turn coil to the feed point at the center of the antenna.

  • Page 13: Use As A Signal Generator

    Use as Crystal Checker and Marker Generator Your DM-81 car, be modified as a crystal checker by installing a crystal in Place of the oscillation coil (see Figure 7). You may use either HC-25U or FT-243 crystals. Also, an HC-6U crystal can be checked if plugged into the FT-243 socket.

  • Page 14: Use As An Absorption Frequency Meter

    Turn the SENSITIVITY control ON and adjust to the minimum meter deflection (just before the OFF position of the control), and set the FUNCTION switch to OSC. You can now use your DM-81 as an absorption frequency meter to receive external energy and indicate its frequency on the meter.

  • Page 15: Use As A Field-strength Meter

    RF and DC circuits. Use as a Field-Strength Meter Your DM-81 can be used to measure the field strength of a transmit antenna. Set up as directed in APPLICATIONS: "Use as Absorption frequency meter". In addition, couple to an antenna as in Figure 9. You can now measure field strength.

  • Page 16: Capacitance And Inductance Measurements

    KENWOOD DM-81 Capacitance and Inductance Measurements The value of an unknown inductor can be obtained in combination with a known capacitor by their resonant frequency, as illustrated in Figure 10. Likewise the value of an unknown capacitor can be calculated. The inductance (L), capacitance (C), and resonant frequency (f) are related as: f = 1 / (2π...

  • Page 17

    Also, your DM-81 can serve as a BFO for a receiver without one in receiving a CW or SSB signal. It is useful in a wide variety of situations. By fully understanding the principles of operation your DM-81's capabilities may be extended to other applications.

  • Page 18

    KENWOOD DM-81...

  • Page 19: Adjustment

    KENWOOD DM-81 ADJUSTMENT VR1: 01 Bias adj. By using G band, adjust VR1 so that the meter pointer deflection is maximum at 83MHz. VR2: Meter zero adj. Adjust VR2 so that the meter deflection is zero when the sensitivity control/power switch is set to just before the OFF position of the control.

  • Page 20: Parts List

    KENWOOD DM-81 Please mention the model and serial number of your unit in any correspondence, whether phone or written. For future reference, record this information in the space provided on the back cover of this manual. NOTE: When claiming warranty service, please include a photocopy of the bill of sale, or other proof of purchase showing the date of sale.

  • Page 21

    KENWOOD DM-81 E29-0524-08 Probe CAPACITOR E30-1839-08 Ground clip Electrolytic CE04W1C100 10µF 16WV E91-0401-08 Battery snap SEMI-CONDUCTOR Insulating F20-0619-08 plate FET 2SK19 (GR) Packing case H01-2914-08 (inside) Transistor 2SA719 Pad (formed H12-0533-08 styrene) Zener diode RD-6, 2EB H19-0507-08 Accessory box MISCELLANEOUS...

  • Page 22

    KENWOOD DM-81 Battery 006P Carbon resistor R5,8 RD14BB2E103J 10K ±5% Ceramic ¼W C12 CC45SL2H050C capacitor 5pF 500WV Carbon resistor RD14BB2E472J Ceramic 4.7K ±5% C13 CK45D1H103M capacitor ¼W 0.01µF ±20% Carbon Carbon resistor RD14BB2E221J resistor 220 R17 RD14BB2E393J 39K ±5% ±5% ¼W ¼W...

  • Page 23

    KENWOOD DM-81 Transistor 2SC945 (K) D1,2 Diode 1SS16 MISCELLANEOUS Feri-inductor L33-0262-08 Printed J25-2887-08 circuit board...

  • Page 24: Printed Circuit Boards

    KENWOOD DM-81 PRINTED CIRCUIT BOARDS...

  • Page 25

    KENWOOD DM-81...

  • Page 26: Schematic Diagram

    KENWOOD DM-81 SCHEMATIC DIAGRAM Unless otherwise specified, resistors are ¼W and ±5%. Also, the circuit elements may be changed without notice owing to a technical innovation.

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