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MULTIVOLTAGE_POWER_SUPPLY

Published:2009-6-26 3:49:00 Author:Jessie

MULTIVOLTAGE_POWER_SUPPLY
This dual-polarity, multivoltage power supply can be built for a very small investment. The circuit is built around 78XX and 79XX series 1-A voltage regulators, four 3-A diodes, a 24-30-V 2-6-A transformer, and eight filter capacitors.   (View)

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UNIVERSAL_MOTOR_SPEED_CONTROL

Published:2009-6-26 3:46:00 Author:Jessie

UNIVERSAL_MOTOR_SPEED_CONTROL
The resistor capacitor network R1-R2-C1 provides a ramop-type reference voltage superimposed on top of a dc volatage adjustable with the speed-setting potentiometer R2.This reference voltage appearing at the wiper of R2 is balanced against the residual counter emf of the motor through the SCR gate.As the motor slows down due to heavy loading,its couter emf falls,and the reference ramp triggers the SCR earlier in the ac cycle.More voltage is thereby applied to the motor causing it to pick up speed again.Performance with the C106 SCR is particularly good because the low trigger current requirements of this device allow use of a flat top reference voltage, which provides good feedback gain and close speed regulation.   (View)

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CMOS_LINE_RECEIVER

Published:2009-6-26 3:45:00 Author:Jessie

CMOS_LINE_RECEIVER
The trip point is set half way between the supplies by R1 and R2; R3 provides over 200 mV of hysteresis to increase noise immunity.Maximum frequency of operation is about 300 kHz. If response to TTL levels is desired, change R2 to 39 K. The trip point is now cen-tered at 1.4 V.   (View)

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SIMPLE_LF_CONVERTER

Published:2009-6-26 3:44:00 Author:Jessie

SIMPLE_LF_CONVERTER
This converter allows coverage from 25 kHz up to 500 kHz. Use short coax from the converter to receiver antenna input. Tune the receiver to 3.5 MHz, peak for loudest crystal calibrator and tune your receiver higher in frequency to 3.6 MHz and you're tuning the 100 kHz range. 3.7 MHz puts you at 200 kHz, 3.8 MHz equals 300 kHz, 3.9 MHz yields 500 kHz, and 4.0 MHz gives you 500 kHz.   (View)

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INVERTING_POWER_SUPPLY

Published:2009-6-26 3:43:00 Author:Jessie

INVERTING_POWER_SUPPLY
This circuit will provide a negative dc voltage that is approximately equal to the positive input voltage at no load and about 3 V less at 10 mA load. VIN is from +5 to +15 Vdc, Do not exceed 15 V or U1 might be damaged.   (View)

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FM_RADIO

Published:2009-6-26 3:43:00 Author:Jessie

FM_RADIO
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ANALOG_RECEIVER_LOW_TEMPERATURE_DRIFT

Published:2009-6-26 3:41:00 Author:Jessie

ANALOG_RECEIVER_LOW_TEMPERATURE_DRIFT
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SIMPLE_NEGATIVE_SUPPLY_FOR_LOW_CURRENT_APPLICATIONS

Published:2009-6-26 3:41:00 Author:Jessie

SIMPLE_NEGATIVE_SUPPLY_FOR_LOW_CURRENT_APPLICATIONS
This dc negative-voltage generator based on the 555 produces a negative output voltage equal to approximately 2x the dc supply voltage.   (View)

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TRANSMATCH

Published:2009-6-26 3:04:00 Author:Jessie

TRANSMATCH
Tapped variable inductance and titree broadcast tuning capacitors are easily preadjusted to match low-power (QRP) transmitter to antenna for SWR of 1 in commonly used amateur bands. Resistance bridge is used only for initial determination of correct settings for C1, C2, C3, and S2 at each band to be used.Set S1 at n, feed peak output of transmitter to J1 (5 W maximum), and adjust R4 for full.scale frequency to be used. Repeat procedure with reading of M1. Next, conned 50.ohm resistive antenna or feed line in place of dummy load, load between CR1-R1 junction and ground. Meter reading should now drop to zero, indicating null at 50 ohms,Move 50-ohm dummy load to J2, set S1 at 2, and adjust seetings of C1,C2, and C3 for zero deflection of meter,Note settings, then repeat for each other transmitter frequency to be used. Repeat procedure with antenna or feed line in place of dummy load, After completing adjustments, set S1 to 3 to bypass bridge for normal transmitter opetation.-D. DeMaw, A Poor Ham's QRP Transmatch, QST, Oct. 1973, p 11,13.   (View)

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LINEAR_VOLTAGE_RAMP_GENERATOR

Published:2009-6-26 3:03:00 Author:Jessie

LINEAR_VOLTAGE_RAMP_GENERATOR
LINEAR_VOLTAGE_RAMP_GENERATOR

In the monostable mode, the resistor can be replaced by a constant current source to provide a linear ramp voltage. The capacitor still charges from 0 to 2/3 Vcc. The linear ramp time is given by the following equation:If VB is much larger than VBE, then t can be made independent of Vcc.   (View)

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1_kHz_MODULATOR_FOR_VHF_SOURCE

Published:2009-6-26 3:02:00 Author:Jessie

1_kHz_MODULATOR_FOR_VHF_SOURCE
Used with 144-MHz signal generator driving VSWR bridge, for measuring and matching VHF antennas. R1 adjusts frequency of NE555 timer used in place of customary MVBR. Series-pass transistor increases output of MVBR about 2 dB.-J. Reisert, Matching Techniques for VHF/UHF Antennas, Ham Fladio, July 1976, p 50-56.   (View)

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STAIRCASE_GENERATOR

Published:2009-6-26 3:01:00 Author:Jessie

STAIRCASE_GENERATOR
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LOGARITHMIC_WATTMETER

Published:2009-6-26 2:59:00 Author:Jessie

LOGARITHMIC_WATTMETER
Single meter scale covers 1-1000W, with equally spaced divisions for 1,10,100,and 1000. This log scale makes it possible to measure very low reflected powers and very high forward powers simultaneously with same percentage accuracy. Basis of operation is that voltage dropped across forward-biased 1N40C2 silicon PN junction diode is proportional to logarithm of cur rent through it. For 50-ohm line, use 220 for R2 and 27 for R3 and R4. For 75 ohm Iine, coffesponding values are 180 and 33. Detectordiodes are point-contact germanium rated at 80 PIV. Article gives construction details. Ground coax braid at one end only. Ferrite ring is 0.5-inch Mullard FX1596 or equivalent.-P.G.Martin, Some Directional Wattmeters and a Novel SWR Meter, 73Magazine,Aug.1974,p 17,19-21,23-24,and 26.   (View)

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HIGH_SPEED_VOLTAGE_OUTPUT_DAC

Published:2009-6-26 2:57:00 Author:Jessie

HIGH_SPEED_VOLTAGE_OUTPUT_DAC
HIGH_SPEED_VOLTAGE_OUTPUT_DAC

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±10_V_FULL_SCALE_UNIPOLAR_DAC

Published:2009-6-26 2:51:00 Author:Jessie

±10_V_FULL_SCALE_UNIPOLAR_DAC
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16_BIT_BINARY_DAC

Published:2009-6-26 2:43:00 Author:Jessie

16_BIT_BINARY_DAC
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8_BIT_D_A_WITH_OUTPUT_CURRENT_TO_VOLTAGE_CONVERSION

Published:2009-6-26 2:40:00 Author:Jessie

8_BIT_D_A_WITH_OUTPUT_CURRENT_TO_VOLTAGE_CONVERSION
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±10_V_FULL_SCALE_BIPOLAR_DAC

Published:2009-6-26 2:37:00 Author:Jessie

±10_V_FULL_SCALE_BIPOLAR_DAC
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PRECISION_12_BIT_D_A_CONVERTER

Published:2009-6-26 2:35:00 Author:Jessie

PRECISION_12_BIT_D_A_CONVERTER
PRECISION_12_BIT_D_A_CONVERTER

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NOISE_BRIDGE

Published:2009-6-26 2:31:00 Author:Jessie

NOISE_BRIDGE
NOISE_BRIDGE
NOISE_BRIDGE

Used with communication receiver to measure impedance at antenna terminals or at end of transmission line, as required for adjusting antenna matching and loading devices for desired impedance at specific frequency. Consists of diode.connected transistor broadband,noise generator, 3-stage noise amplifier, and toroid transformer bridge. All transistors are 2N5129 or equivalent 2N5137 or 2N5220. Try different transistors until highest noise output is obtained. Toroid core for trans.former is 3/8-inch Indiana General CF102. Quadrifilar winding has 4 1/2 turns of four No.28 enamel wires twisted together, wound on core and connected as on diagram. Noise bridge can also serve as wideband noise source for signal injection during troubleshooting in AF or RF circults, and as noise source for aligning RF cir-cuits,-J.J. Schultz, An Improved Antenna Noise Bridge, CQ, Sept, 1976, p 27-29 and 75.   (View)

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