DIGITAL_THERMOMETER

Published:2009/6/26 1:41:00 Author:May

The sensor consists of two series-connected 1N914s, part of the circuit of a 555 multivibrator. Wired as shown, the output pulse rate is proportional to the temperature of the diodes. This output is fed to a simple frequency-counting circuit.   (View)

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SWR_T0_500_MHz

Published:2009/6/25 23:47:00 Author:May

Permits measuring standing-wave ratio well above limits of many inex-pensive indicators. Fot transmitters up to 2 W, coupling loop L1-L2 can be about 1 inch long.For high-power transmitters, loop length can be reduced to about 1/8 inch.-W. E. Parker, UHF SWR Indicator, 73 Magazine, June 1977, p 68-70.   (View)

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PRECISION_FULL_WAVE_RECTIFIER

Published:2009/6/25 23:42:00 Author:May

Circuit Notes The circuit provides accurate full wave rectification. The output impedance is low for both input polarities, and the errors are small at all signal levels. Note that the output will not sink heavy current, except a small amount through the 10 K resistors. Therefore, the load applied should be referenced to ground or a negative voltage. Reversal of all diode polarities will reverse the polarity of the output. Since the outputs of the amplifiers must slew through two diode drops when the input polarity changes, 741 type devices give 5% istortion at about 300 Hz.   (View)

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AC_MOTOR_BRAKE

Published:2009/6/25 23:37:00 Author:May

A shot of direct current will instantly stop any ac power tool motor. Switch S1 is a center-off, one side spring return. With S1 on, ac will be fed to the motor and the motor will run. To brake the motor, simply press S1 down and a quick shot of dc will instantly stop it. The switch returns to the center off position when released. This Power Brake can only be used with ac motors; it will not brake universal (ac-dc) motors. A heat sink must be provided for the diode.   (View)

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FM_DEMODULAT0_R_AT_12_V__

Published:2009/6/25 23:28:00 Author:May

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80_METER_DIRECT_CONVERSION

Published:2009/6/25 23:28:00 Author:May

Portabl e receiver with directional ferrod antenna and ver-tical sense antenna was developed for radio foxhunting at 1975 Bov Scout World Jamboree in Norway, in competitions for locating four low-power crystal-controlled transmitters hid-den along 4-km course. Varactor-tuned oscillator provides 20-kHz tuning range with R9, ade-quate for the frequency used-3.566, 3.585, 3.635, or 3680 MHz. T1 is subminiature auto-transformer with 8-ohm and 2000-ohm sec-tions, for 8-ohm headphones. For high-imped-ance headphones, connect headphone jack J1 to lug 9 of T1. ON/OFF switch is not needed, L1 is 22 turns No. 28 enamel wound over two 10×95 mm ferrite rodstaped together. 01-06 are NPN high-frequency small-signal transistors.-N. K. Holter, Radio Foxhunting in Europe, QST, Nov. 1976, p 43-46.   (View)

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5_STEP_ATTENUATOR

Published:2009/6/25 23:27:00 Author:May

AppIication s indude comparing performance of various rece Mng an-tennas and measuring gain of preamp used abead of receiver. Dashed lines represent required shield partitions. All resistors are 1/4-W composition with 5% tolerance.-D.DeMaw, What Does My S-Meter Tell Me?, QST,June 1977,p 40-42.   (View)

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RF_BRIDGE_FOR_COAX

Published:2009/6/25 23:27:00 Author:May

Simplifies adjustment of vertical antenna for 40, 80, and 160 meters.S1 in add-on LC unit switches coil for desited band. Values of C1-C4 and standard resistor R1 give range of 10 to 150 ohms for measurement of radiation resistance. Meter can be from 50 to 200μA full scale if 500 mW of power is available as signal source. For shorter-wavelength bands, change resistance in parallel with J1 to 5600 ohms and omit C6. L1 for 10 meters should then have 3 1/2 tums No. 18 spaced to occupy 1/4 inch on Miller4200 coilform. L2(15 meters) is Gtums No. 16 enamel closewound on similar form. L3 (20 meters) is 11 turns No.14 enamel on Miller 66A022-6 form.-J. Sevick, Simple RF Bridges, OST, April 1975, p 11-16 and 41.   (View)

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SELF_EXCITED_SWR_BRlDGE

Published:2009/6/25 23:19:00 Author:May

Portable bridge has built-in signal sources for each band from 80 through 10 meters, for tuning antenna on tower before transmission line is connected.Oscillators are crystal controlled at desired antenna tuneup frequencies. Separate oscillators for each band simplify switching problems, so only supply voltage from J1 and oscillator outputs to meter circuit need be switched. Current drain from 9-V battery is maximum of 12 mA.R17 and R18 should be closely matched, while R1, and R20 should have 5% tolerance.-T.P.Hulick, An S.W.R.Bridge with a Built-In 80 Through 10 Meter Signal Source, CQ1 June 1971,p 64-66 68, and 99.   (View)

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HALF_WAVE_RECTIFIER

Published:2009/6/25 23:06:00 Author:May

Circuit Notes This circuit provides for accurate half wave rectification of the incoming signal. For positive signals, the gain is 0; for negative signals, the gain is -1. By reversing both di-odes, the polarity can be inverted. This circuit provides an accurate output, but the output impedance differs for the two input polarities and buffering may be needed. The output must slew through two diode drops when the input polarity reverses. The NE5535 device will work up to 10 kHz with less ttan 5% distortion.   (View)

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LADDER_ATTENUATOR

Published:2009/6/25 22:51:00 Author:May

Inserted in series with receiving antenna to provide 5 steps of attenuation for comparing performance of anten-nas or preamps. Resistors are 1/4-W composition with 5% tolerance.-D. DeMaw, What Does My S-Meter Tell Me?, QST, June 1977, p 40-42.   (View)

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DELAYED_BRAKE

Published:2009/6/25 22:48:00 Author:May

Protects antenna rotator on high tower from damage by delaying brake ac-tion automatically after rotation and by disa-bling direction-selector switches so antenna system coasts to stop before rotation can begin in other direction. For about 3.s delay in timer U4, use 2.2 megohms for R and 1μF for C instead of values shown. RV1 is commonly listed as V150LA20A by GE.S3-S5 are original brake release and direction switches in CDE Hamllrotor system，Article coners construction and installation, including modifications needed Incontrol unit．－A．B，White,A Delayed Brake Release for the Ham-ll,QST， Aug.1977、p14- 16   (View)

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FULL_WAVE_RECTIFIER_AND_AVERAGING_FILTER

Published:2009/6/25 22:45:00 Author:May

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TELEMETRY_DEMODULATOR

Published:2009/6/25 22:44:00 Author:May

Circuit NotesThe circuit recovers an FM audio signal that varies from less than 1 kHz to about 10 kΗz   (View)

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10_MHz_WITH_30_dB_GAIN

Published:2009/6/25 22:42:00 Author:May

CA3000 IC is operated as RF amplifier with single-ended inputand output, With appropriate tuned circuits, amplifier performs well up to 30MHz，－E.M.Noll,″Linear IC Principles,Experiments, and Projects、″Howard W.Sams.Indianapolis、IN,1974、p91-92   (View)

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TELEPHONE_LINE_POWERED_REPERTORY_DIALER

Published:2009/6/25 22:26:00 Author:May

Repertory dialer phone has a library of fifteen frequently used numbers，（plus the last number dialed）stored In a standard CMOS RAM，A pushbutton keyboardenables telephone numbers to be keyed in and dialed out directly or a telephone number to be stored in the RAM and dialed automatically.   (View)

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70_dB_VOLTAGECONTROLLED_GAIN

Published:2009/6/25 22:24:00 Author:May

Amplifier Q1 uses current source Q2 as emitter resistor to provide correct current bias for class A operation. Coupling through 150-μF capacitor to silicon diode string D1-D8 provides variable re-sistance needed to achieve variable gain. Sim-ple differential amplifier Q3-Q4 adjusts forward bias of diodes to change their forward resis-tanco. Increasing positive control voltage from 0 to 4.5 V changes voltage gain from -74 dBm to about -4 dBm with respect to 0-dBm input signaL-N.A Steiner, Voltage-Controlled Am-plifier Covers 70 dB Range, EDN Magazine, March 5, 1975, p 72 and 74.   (View)

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FET_CASCODE_VIDEO

Published:2009/6/25 22:22:00 Author:May

Use of 2N5485 FETs gives very low input loading, with feedback reduced almostto zero，Bandwidth of amplifier is limited only by load resistance and capacitance．-″FET Databook,″ National Semiconductor,Santa Clara,CA,1977、p 6-26-6-36   (View)

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40_265_MHz_VMOS

Published:2009/6/25 22:21:00 Author:May

Wideband power amplifier using Siliconix Mospower FET in negative-feed-back circuit has flat gain within 0.5 dB over entire operational range of 40 to 265 MHz. Use 6 to 8 turns of No.30 on 1/2-W 1-megohm resistor for L1 (not commercially molded choke). T1 is 4 turns No.22 twisted- pair on Indiana General F625-902 toroid core. Avoid static charges until transistor is soldered into circuit.-E. Oxner, Mospower FET as a Broadband Amplifier, Ham Radlio, Dec.1976, p 32-35.   (View)

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TELEPHONE_CONTROLLED_TAPE_STARTER_TCTS

Published:2009/6/25 22:18:00 Author:May

This circuit converts a tape recorder into a completely automatic telephone conversation recording instrument that needs no external power source. Voltage at the switch terminals of tape recorder applied to a pair of Darlington-connected transistors, Q1 and Q2, will turn on and start the tape recorder. To turn the transistors off, and thereby stop the machine, apply a negative voltage to the base of Q1 from the phone line. When the telephone receiver is on the hook, there is typically about 50 volts dc across the phone divided across R1, R2, and R4 in such a way that the base of Q1 is sufficiently negative to keep the tape recorder off. When the phone's receiver is picked up, the voltage on the telephone line drops to about 5 volts, which leaves insufficient negative vol-tage on the base of Q1 to keep it cut off, so the tape recorder starts and begins to record.   (View)

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