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KENWOOD  DM-81

 

18 

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.  

PARTS LIST 

MAIN CHASSIS  

Ref. 
# 

Part #  

Description  

 

A01-0859-08  

Case top  

 

A01-0860-08  

Case bottom  

 

A09-0506-08  

Coil case  

 

A10-0471-28  

Chassis  

 

A29-0502-08  

Top panel  

 

B20-0918-28  

Dial scale  

 

B23-0602-08  

Front glass  

 

B31-0719-08  

Meter  

 

B40-0772-08  

Name plate 
(serial #)  

 

B50-2920-00  

Instruction 
manual  

 

C01-0191-08  

Variable 
capacitor  

 

E11-0061-08  

Pin jack  

 

E13-0101-05  

Phone jack  

 

E18-0207-08  

Crystal socket 
(FT-243)  

 

E18-0402-08  

Crystal socket 
(HC-25U)  

  

AMP UNIT (X73-1350-00)  

Ref. 
# 

Part #  

Description  

RESISTOR  

R11   RD14BB2E563J  

Carbon resistor 
56K

Ω

 ±5% 

¼W  

R12   RD14BB2E124J  

Carbon resistor 
120K

Ω

 ±5% 

¼W  

R13   RD14BB2E683J  

Carbon resistor 
68K

Ω

 ±5% 

¼W  

R14   RD14BB2E472J  

Carbon resistor 
4.7K

Ω

 ±5% 

¼W  

R15   RD14BB2E222J  

Carbon resistor 
2.2K

Ω

 ±5% 

¼W  

R16   RD14BB2E561J  

Carbon resistor 
560

Ω

 ±5% ¼W  

VR2   R12-2506-08  

Semi-fixed 
resistor 5K

Ω

  

VR3   R05-3002-08  

Variable 
resistor (with 
SW) 1OK

Ω

B 

Содержание DM-81

Страница 1: ...er 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 Sensitivit...

Страница 2: ...KENWOOD DM 81 ...

Страница 3: ...cillating energy is absorbed by the circuit thus decreasing the oscillation strength This strength is indicated on the meter The pointer 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 ch...

Страница 4: ...KENWOOD DM 81 2 ...

Страница 5: ...ceivers when using your DM 81 as a signal generator Also when used as the marker generator amplitude modulation is helpful in precisely calibrating the dial scale even for a receiver having no BFO 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 A...

Страница 6: ...s Crystal oscillator element to be used HC 25U and FT 243 RF search terminal For measuring resonant frequency capacitive coupling and checking RF voltage using the supplied probe Earphone terminal Accepts crystal earphone with 3 5ø plug for monitoring modulated tone Dimensions 70W x 180H x 45D mm Weight Approx 690g with accessories Accessories 1 Coils A G bands 7 pieces 2 Probe 1 piece 3 Ground cl...

Страница 7: ...KENWOOD DM 81 5 CONTROLS ...

Страница 8: ...er is brought to the resonant circuit being checked the tighter the two are coupled and the deeper the dip point However the tuning point becomes so broad that you cannot find the correct resonant frequency Therefore it is advisable to move the dip meter a little away from the circuit Note that the A band has a large pull in effect and therefore the dip point is broad Measuring Transistor Resonant...

Страница 9: ...he FUNCTION switch to OSC 4 Turn the power on 5 Turn the SENSITIVITY control until the meter pointer reads at division 0 7 If not to division 0 7 turn the control fully counter clockwise 6 Bring the dip meter coil about 1 cm from the tuned circuit to be measured and slowly turn the dial The oscillator signal energy will be absorbed by the tuned circuit at the resonant point and the meter will dip ...

Страница 10: ...citors 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 Use of the capacitive probe If a coil to be measured is located in a narrow place and cannot be coupled to the dip meter coil or if a coil is enclosed in a shield the probe can be used for accurate measurement See Figure 4 ...

Страница 11: ...z 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 See connections a through e in the illustration The dip point is sometimes critical depending on the circuit or frequency to be measured An accurate dip point can be obtained by turning the dial slowly ...

Страница 12: ... at the center of the antenna Couple it with the dip meter coil Now you can obtain the antenna resonant frequency in a similar manner to APPLICATIONS Section A For a vertical antenna or similar antennas for which the other feeder lead is grounded place the one turn coil between the antenna and ground Couple the one turn coil to the dip meter until a dip point is obtained Then slowly separate the c...

Страница 13: ...rs can be achieved by leaving the switch at OSC for no modulation Adjust the capacitor trimmers and inductor cores for maximum receiver S meter reading or maximum speaker output 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 c...

Страница 14: ... 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 Figure 8a shows how to measure oscillator frequency The oscillator coil is coupled with or brought near the absorption frequency meter coil Adjust the dial for maximum meter deflection and read the oscillation frequency Figure 8b shows the absorption frequency mete...

Страница 15: ...ls Observe normal safety procedures for high 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 This application is convenient for transmit antenna matching radiation pattern ...

Страница 16: ...wn 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 LC This formula can be rewritten as L 25 400 f C C 25 400 f L Where L inductance in µH C capacitance in pF f frequency in MHz ...

Страница 17: ... In addition to all these applications your DM 81 is usable in place of a receiver local oscillator in repairing or alignment and is effective in other services as well 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...

Страница 18: ...KENWOOD DM 81 16 ...

Страница 19: ...witch is set to B C position PARTS AND SERVICE Ordering Spare Parts When ordering replacement or spare parts for your equipment be sure to specify the following Model and serial number Schematic number of the parts Printed circuit board number on which the part is located Part number and name if known and quantity desired Service Should it ever become necessary to return this equipment for repair ...

Страница 20: ...s A29 0502 08 Top panel B20 0918 28 Dial scale B23 0602 08 Front glass B31 0719 08 Meter B40 0772 08 Name plate serial B50 2920 00 Instruction manual C01 0191 08 Variable capacitor E11 0061 08 Pin jack E13 0101 05 Phone jack E18 0207 08 Crystal socket FT 243 E18 0402 08 Crystal socket HC 25U AMP UNIT X73 1350 00 Ref Part Description RESISTOR R11 RD14BB2E563J Carbon resistor 56KΩ 5 W R12 RD14BB2E12...

Страница 21: ...uit 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 10µF 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 ...

Страница 22: ...ncy unit R5 8 RD14BB2E103J Carbon resistor 10KΩ 5 W R9 RD14BB2E472J Carbon resistor 4 7KΩ 5 W R10 RD14BB2E221J Carbon resistor 220Ω 5 W VR1 R12 3511 08 Semi fixed resistor 20KΩB CAPACITOR C1 CC45SL1H470J Ceramic 47pF 5 C2 CC45SL1H030C Ceramic 3pF 0 25pF C3 CC45SL1H010C Ceramic 1pF 0 25pF C4 CK45D1H103M Ceramic 0 01µF 20 C5 7 CK45D1H102M Ceramic 0 001µF 20 C6 CC45SL1H101J Ceramic 100pF 5 C8 10 CQ92...

Страница 23: ...KENWOOD DM 81 21 Q2 Transistor 2SC945 K D1 2 Diode 1SS16 MISCELLANEOUS L33 0262 08 Feri inductor 2mH J25 2887 08 Printed circuit board ...

Страница 24: ...KENWOOD DM 81 22 PRINTED CIRCUIT BOARDS ...

Страница 25: ...KENWOOD DM 81 23 ...

Страница 26: ...KENWOOD DM 81 24 SCHEMATIC DIAGRAM Unless otherwise specified resistors are W and 5 Also the circuit elements may be changed without notice owing to a technical innovation ...

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