Digital Circuit

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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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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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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VHF_MODULATOR

Published:2009/6/25 22:17:00 Author:May

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4PULSE_WIDTH_MODULATOR

Published:2009/6/25 22:16:00 Author:May

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3PULSE_WIDTH_MODULATOR

Published:2009/6/25 22:14:00 Author:May

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TONE_DIAL_SEQUENCE_DECODER

Published:2009/6/25 22:14:00 Author:May

The circuit takes active low inputs from a Touch Tone decoder and reacts to a proper sequence of digits. The proper sequence is determined by which Touch Tone digits the user connects to the sequence decoder inputs TT1, TT2, TT3, and TT4.   (View)

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TONE_DIAL_ENCODER

Published:2009/6/25 22:13:00 Author:May

Tone dial encoder with automatic PTT control uses the 555 timers.   (View)

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AM_MODULATOR

Published:2009/6/25 22:11:00 Author:May

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2PULSE_WIDTH_MODULATOR

Published:2009/6/25 22:10:00 Author:May

The monostable circuit is triggered by a continuous input pulse train and the threshold voltage is modulated by a control signal. The resultant effect is a modulation of the output pulse width, as shown. A sine-wave modulation signal is illustrated, but any wave-shape could be used.   (View)

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MODULATOR_

Published:2009/6/25 22:09:00 Author:May

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BALANCED_MODULATOR_（＋12_Vdc_SINGLE_SUPPLY）

Published:2009/6/25 22:09:00 Author:May

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VIDEO_MODULATOR_

Published:2009/6/25 22:07:00 Author:May

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LINEAR_PULSE_WIDTH_MODULATOR

Published:2009/6/25 22:07:00 Author:May

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RE_MODULATOR

Published:2009/6/25 22:05:00 Author:May

Capacitors C1, C3, C5, and C6 should be dipped mica. C4 and C7 are compression or piston trimmer types. R6 is PC-board mount trimpot. L1 is 6 tums of No.14 enameled wire, 3/8 inch I.D. by 3/4 inch long, tapped at 1 turn from top.   (View)

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