Kenwood DM 81 Service Manual

Page 1

KENWOOD DM-81

Page 2

KENWOOD DM-81 1 INTRODUCTION A dip meter is used for adjustment of radio equipme nt and antennas. The DM-81 is a self-excited oscillator designed for external coupl ing to the equipment being tested. It features both inductive and capacitive coupling for measuring enclosed coils and toroidal coils (patent pending). This is not possible with c onventional testing instruments. The DM-81 has the following two functions: Inductive coupling As shown (Figure 1A), place the coil unit of the di p meter in close proximity to the circuit being measured. Adjust the dial. When the dip meter oscillation fre quency coincides with the resonant frequency (tuned circuit), oscillating ene rgy is absorbed by the circuit, thus decreasing the oscillation strength. This strength is indicated on the meter. The pointe r swings back momentarily at the resonant point. Since the meter pointer dips at a tuned point, this instrument is called a dip meter. 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 tou ching the capacitance probe to the hot side of the resonant circuit under test, instead of coupling the DM-81's coil and measuring inductively. The frequency is re ad directly on the dial. See Figure 1B. Radio equipment is miniaturized and most coils are enclosed in metal shields. Also, toroidal coils are used in many types of radi o equipment, and these coils do not couple to conventional dip meters. The DM-81 ha s solved this problem.

Page 20

KENWOOD DM-81 19 E29-0524-08 Probe E30-1839-08 Ground clip E91-0401-08 Battery snap F20-0619-08 Insulating plate H01-2914-08 Packing case (inside) H12-0533-08 Pad (formed styrene) H19-0507-08 Accessory box H25-0165-08 Polyethylene bag H25-0166-08 Polyethylene bag J19-0477-08 Battery holder J21-1460-08 Coil mounting hardware J21-1461-08 Variable capacitor mounting hardware J25-1279-08 Printed circuit board K29-0254-08 Push-button K29-0255-08 Dial L37-0017-08 Coil A L37-0018-08 Coil B L37-0019-08 Coil C L37-0020-08 Coil D L37-0021-08 Coil E L37-0022-08 Coil F L37 -0369 -08 Coil G CAPACITOR C11 CE04W1C100 Electrolytic 10µ F 16WV SEMI-CONDUCTOR FET 2SK19 (GR) Transistor 2SA719 Zener diode RD-6, 2EB MISCELLANEOUS K29-0256-08 Knob J25-2888-08 Printed circuit board HIGH FREQUENCY UNIT (XB4-1040- 00) Ref. # Part # Description RESISTOR R1 RD14BB2E562J Carbon resistor 5.6K ±5% ¼W R2,6,7 RD14BB2E124J Carbon resistor 120K ±5% ¼W R3 RD14BB2E222J Carbon resistor 2.2K ±5% ¼W R4 RD14BB2E471J Carbon resistor 470 ±5% ¼W

Page 25

KENWOOD DM-81 24 SCHEMATIC DIAGRAM Unless otherwise specified, resistors are ¼W and ±5%. Also, the circuit elements may be changed without notice owing to a technical innovation.