DIY Antennas, QRP, SDR & Ham Radio Projects from VU3DXR
The Circuits category focuses on stand‑alone electronic building blocks that power your radio and audio projects: amplifiers, oscillators, filters, keyers, indicators, test jigs, and more. Instead of full transceivers or big systems, you’ll find focused designs like microphone preamps, push‑pull HF linear amplifiers with IRF510, regenerative receivers, short‑wave transmitters, low‑battery indicators, and timing circuits
The LM1458 is a dual operational amplifier (op-amp) that finds applications in audio amplification and other circuits. Let’s explore how you can create a simple Microphone compressor using the LM1458. To get greater transmitting performance from your ham radio transceiver, we need to keep the modulation level constant, regardless of your voice level. With the compressor […]
The compact, low-cost condenser mic amplifier described here give good-quality audio of 0.5 watts at 4.5 volts,used in walkietalkies, low-power transmitters
This dual-microphone noise cancellation circuit uses two microphones placed back-to-back, with one signal inverted and summed using an LF351 op-amp to cancel common ambient noise. It preserves the desired voice signal while reducing background noise, improving clarity in noisy environments
This series-modulated AM transmitter uses a simple low-power design where the audio signal is applied directly to the power supply of the RF oscillator, causing the carrier amplitude to vary and produce AM. It uses a crystal oscillator for stable frequency and is ideal for beginners learning basic radio transmission concepts.
This Class C AM transmitter uses a high-efficiency amplifier where the transistor conducts for less than half the signal cycle, achieving around 70–80% efficiency. It combines an oscillator, buffer, and IRF510 MOSFET power stage to deliver about 5 W RF output, making it suitable for compact amateur radio transmission.
This noise-canceling condenser microphone design uses dual electret microphones with op-amp stages to reduce ambient noise. One mic captures the desired audio while the other picks up background noise, which is inverted and summed to cancel interference, improving clarity for communication and recording.
This microphone compressor circuit utilizes a two-stage amplification design for dynamic range control. Initially, the input signal enters through MK1, a microphone input connector. Subsequently, the signal passes through C1 and C3 coupling capacitors for DC blocking. The first amplification stage employs Q1, a 2N3904 transistor configured as a common emitter amplifier. Meanwhile, R1 provides […]
This dynamic speech compressor with audio preamplifier combines a transistor-based preamp and op-amp gain stage with diode-controlled compression to regulate signal levels. It automatically reduces loud peaks and boosts weak audio, delivering consistent output with adjustable threshold, attack, and release timing for clear speech and improved transmission quality.
This simple two-stage AM transmitter uses an oscillator and a transistor RF amplifier to deliver about 1 W output on HF bands. It supports common transistors like BD139 or 2N3553, uses a modulation transformer for audio input, and serves as a beginner-friendly QRP project with stable performance
Build a Simple Series Modulated AM QRP HF Transmitter for the 40m or 80m bands. This DIY guide includes a stable crystal oscillator schematic, series modulation tips, and power amplifier details for low-power (QRP) ham radio operation.