Audio Power Amplifier for AM Radio

This is an AM radio power amplifier circuit. What is different with other general amplifier is that this circuit has a low-pass filter (passive type), built using R1C1 to limit the input-output frequency response. Additionally, a ferroxcube K5-001-001/3B with 3 turns of wire is used as ferrite bead  at output filter. All components should be spaced very close to  the […]

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Monitoring Off-Air Condition

The circuit of off-air monitor for SSB transmitter can be built by using combination of detector product with the crystal oscillator. This circuit is used for testing the audio at one point within band. The quality of audio will still constant, if loading and tuning of SSB transmitter are same over rest of band. The LC circuit will resonated to […]

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Remote Video System Multiplexer

Combination 8 channel multiplexer and amplifier (IC1) is the heart of the remote multiplexer box in the single coax video system. The MUX baseband video output is coupled by C11 to the coax and the video is decoupled by L1 from dc power arriving on the same line. All circuitry in the multiplexer box is supplied by this power (about […]

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Radio Frequency (RF) Watt Meter

For RF (radio frequency) transmitter experiment, watt meter is useful for optimizing the transmitter circuit. A simple RF watt meter circuit is shown in the  schematic diagram below. Because circuit is not frequency sensitive, calibration is accurate on all HF bands. The sensitivity is affected by meter movement, number of turns in primary coil, and resistive voltage driver. Pots can […]

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10W 2 Meters RF Power Amplifier

When operating from 12.5 V auto battery, single TRW PT5757 transistor provides 10 W output. L1 is 4 tums No. 20 enamel and L2 is 10 tums No.20. Both, L1 and L2 has 3/32inch inner diameter. T1 is 4:1 transmission-line transformer made from 3-inch length of twisted-pair No. 20 enamel. This circuit can be used to amplify small transmitter (1W), […]

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