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Kenwood DM-81, Manual, Page: 15 / 26

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Kenwood DM-81 Manual Download Page 15

KENWOOD  DM-81 

 

13 

meter pointer does not deflect off scale. The earphone ahows you to monitor 
modulation.  

WARNING: Tube type power amplifiers operate at high RF and DC potentials. 
Transistorized power amps also produce high RF levels. 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 
adjustments, and similar uses.  

Summary of Contents for DM-81

Page 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...

Page 2: ...KENWOOD DM 81 ...

Page 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...

Page 4: ...KENWOOD DM 81 2 ...

Page 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...

Page 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...

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

Page 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...

Page 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 ...

Page 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 ...

Page 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 ...

Page 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...

Page 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...

Page 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...

Page 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 ...

Page 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 ...

Page 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...

Page 18: ...KENWOOD DM 81 16 ...

Page 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 ...

Page 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...

Page 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 ...

Page 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...

Page 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 ...

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

Page 25: ...KENWOOD DM 81 23 ...

Page 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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