Circuit Diagram

100_W_PEP_420_450_MHz_PUSH_PULL_LINEAR_AMPLIFIER

Published:2009/6/26 4:10:00 Author:Jessie

This 100 watt linear amplifier may be constructed using two MRF309 transistors in push-pull, requiring only 16 watts drive from 420 to 450 MHz. Operating from a 28 volt supply, eight dB of power gain is achieved alongwithexcellent practical performance featuring: maximum input SWR of 2:1, har-monic suppression more than-63 dB below 100 watts output, efficiency greater than 40%, circuit stability with a 3:1 collector mismatch at all phase angles.   (View)

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24_V_TO_33_V_SWITCHING_REGULATOR

Published:2009/6/26 4:08:00 Author:Jessie

The National Semiconductor LM2574 delivers 3.3 V out at O.SAfrom a 24-V source. The duty cycle is:VD ＝ diode drop(0.39)VIND ＝ inductor dc dropVSAT ＝ saturation voltage of LM2574(0.9 V typical)   (View)

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VLF_CONVERTER

Published:2009/6/26 3:51:00 Author:May

This converter uses a low-pass filter instead of the usual tuned circuit so the only tuning required is with the receiver. The dual-gate MOSFET and FET used in the mixer and oscillator aren't critical. Any crystal having a frequency compatible with the receiver tuning range may be used. For example, with a 3500 kHz crystal, 3500 kHz on the receiver dial corresponds to zero kHz; 3600 to 100 kHz; 3700 to 200 kHz, etc. (At 3500 khz on the receiver all one can hear is the converter os-cillator, and VLF signals start to come in about 20 kHz higher.)   (View)

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AUDIO_CONTINUITY_TESTER

Published:2009/6/26 4:05:00 Author:Jessie

This low-current audio continuity tester indicates the unknown resistance value by the frequency of audio tone. A high tone indicates a low resistance, and a tone of a few pulses per second indicates a resistance as high as 30 megohms.   (View)

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NEON_LAMP_DRIVER_FOR_5_TO_15_V_SUPPLIES

Published:2009/6/26 3:51:00 Author:May

This neon-lamp driver based on the 555 T1 can be wound on an old TV flyback transformer core.   (View)

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SQUELCH_CIRCUIT_FOR_AM_OR_FM

Published:2009/6/26 3:50:00 Author:May

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CURRENT_LIMITING_REGULATOR

Published:2009/6/26 3:49:00 Author:May

Floating adjustable regulators can be used as current Iimiters. Resistor R1 programs the current flowing through R2.   (View)

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5_V_TO_33_V_SWITCHING_REGULATOR

Published:2009/6/26 4:05:00 Author:Jessie

A National Semiconductor LM2574 is used to derive 3.3 V at 0.5 A from a 5-V logic bus. The duty cycle is: VD = diode drop (0.39) VIND = inductor dc drop VSAT = saturation voltage of LM2574 (0.9 V typical) This circuit should be useful to derive 3.3 V for logic devices from existing +5-V buses.   (View)

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LOW_PARTS_COUNT_RATIOMETRIC_RESISTANCE_MEASUREMENT

Published:2009/6/26 4:04:00 Author:Jessie

The unknown resistance is put in series with a known standard and a current passed through the pair. The voltage developed across the unknown is applied to the input and the voltage across the known resistor applied to the reference input. If the unknown equals the standard, the display will read 1000. The dis-played reading can be determined from the following expression:Runknown Displayed Reading= ___________ =×1000 RstandardThe display will overrange for Runknown, ≥2× Rstandard.   (View)

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CMOS_LINE_RECEIVER

Published:2009/6/26 3:45:00 Author:May

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:May

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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FM_RADIO

Published:2009/6/26 3:43:00 Author:May

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ANALOG_RECEIVER_LOW_TEMPERATURE_DRIFT

Published:2009/6/26 3:41:00 Author:May

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FM_STEREO_DEMODULATION_SYSTEM

Published:2009/6/26 3:40:00 Author:May

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AM_RADIO

Published:2009/6/26 3:39:00 Author:May

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INDUCTORLESS_POWER_SUPPLY_CONVERTER

Published:2009/6/26 3:39:00 Author:May

Using a 555 timer and voltage doubler, this circuit will supply ≥50mA at 20 Vdc. T1 and T2 act as power amplifiers to drive the voltage doubler. Frequency of operation is approximately 8.5 kHz.   (View)

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AM_FM_CLOCK_RADIO

Published:2009/6/26 3:38:00 Author:May

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HV_POWER_SUPPLY_WITH_9_TO_15_Vdc_INPUT_

Published:2009/6/26 3:38:00 Author:May

The combination Hartley oscillator/step-up transformer shown in A can generate significant negative high voltage, especially if the voltage output of the transformer is multiplied by the circuit in B.   (View)

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COMBINATION_VOLTAGE_AND_CURRENT_REGULATOR

Published:2009/6/26 3:35:00 Author:May

This voltage-regulator/current-limiter combination can be made from two 7805 regulators as shown. R1, R2, and R3 should be selected for a 5-V drop at the maximum allowable current limit. S1 selects one of the three current values. Do not forget that U1 requires 5 mA to operate and this means that the minimum current limit setting should be 10 mA or more (R1 = 1.25 kΩ). Resistor values are as follows:   (View)

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CONFIGURABLE_POWER_SUPPLY

Published:2009/6/26 3:18:00 Author:May

The adjustable supply can easily be reconfigured by altering the value of V2 and beefing up some other components, as is necessary. The output voltage is given by VOUT = 1.25 (1 + R2/R1) . R2 can be chanced, as is necessary.   (View)

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