DIY Antennas, QRP, SDR & Ham Radio Projects from VU3DXR
The HF category brings together all content related to high‑frequency bands, from 160 m through 10 m, with emphasis on practical antennas, propagation, and station hardware. Here you will find compact 40 m verticals, multiband wire antennas, HF QRP transmitters, SDR transceivers, and accessories designed for real‑world home and portable operation. Articles often include measured SWR curves, on‑air reports, and build photos so you can understand how a design will behave before you start cutting wire.
There is a strong focus on getting HF on the air from small Indian plots, apartments, and field locations without sacrificing too much performance. Whether you are preparing for your first HF QSO, improving your 40 m NVIS coverage, or chasing DX on higher bands during good conditions, this section provides tested ideas to upgrade your HF station step by step
This micro power AM transmitter uses a crystal-controlled oscillator and a 2N2222 transistor stage to generate a stable RF carrier, then modulates it with audio input. A tuned tank circuit and variable capacitor optimize output, enabling low-power short-range broadcasting for experimentation and learning
This microphone audio compressor for SSB radio combines a low-noise preamplifier with automatic gain control to maintain consistent speech levels. It boosts weak audio and limits peaks, improving average modulation and clarity without distortion, making transmissions more intelligible, especially in low-power HF setups.
This article explains why the MXR Dyna Comp, a guitar compressor pedal, is not suitable for SSB amateur radio use despite being a compressor.
It points out key issues like impedance mismatch, since guitar pedals expect high-impedance inputs unlike microphone or line-level signals used in transceivers. It also highlights that the pedal’s frequency response and controls are designed for musical audio, not narrowband voice signals used in SSB.
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 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.
Simple audio compressor for SSB HF Radio rigs An audio/speech compressor is a device that reduces the dynamic range of the audio signal. This means that it makes the loud parts of the signal quieter and the quiet parts of the signal louder. This can be useful for SSB HF radio rigs because it can […]
This project uses an SSM2167 IC as a complete microphone preamplifier with built-in compression and noise gating to improve uBITX transceiver audio. It boosts mic gain, reduces dynamic range, and suppresses background noise, resulting in clearer, louder, and more consistent transmitted speech.