DIY Antennas, QRP, SDR & Ham Radio Projects from VU3DXR
The audio category collects everything related to sound in your shack: microphone preamplifiers, speech processors, tone generators, practice oscillators, test signals, and audio troubleshooting guides. You’ll find circuits like simple 2N3904 mic preamps for uBITX, audio peak limiters, speech processors, UJT code practice oscillators, pink noise generators, and sine‑wave sources, all tuned for amateur‑radio and hobby use
This article describes a simple microphone compressor built with three transistors to improve audio consistency. The circuit uses a preamplifier, buffer, and feedback stage to control gain. As input increases, negative feedback reduces amplification, compressing louder signals. It runs on 12V and suits amateur radio setups needing stable, balanced voice output.
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.
VK3YE’s AGC circuit for ubitx An ubitx AGC board is a circuit board that can be installed in a ubitx transceiver to provide automatic gain control (AGC). AGC is a feature that automatically adjusts the gain of the transceiver’s amplifier to maintain a constant audio output level, regardless of the strength of […]
LM386 Audio oscillator This one is excellent application of widely used audio amplifier IC LM386.Its output is square wave at no load condition. Its frequency is governed by supply voltage. It can be used as code practice oscillator, even as side tone for your qrp radio. The LM386 is an widely abused integrated circuit containing […]
An NE567 tone decoder, tuned to the transceiver`s CW offset frequency, ensures that the transceiver will be transmitting on the same frequency as the received CW signal. Simply tune the transceiver so that the LED lights. Eight to 13 Vdc is required; this can be taken from the transceiver supply or an extra battery. Audio […]
The Dark Room Timer circuit described here provides a pleasant musical tone in your darkroom at 1-second intervals. The circuit takes up very little space and can be easily converted into a metronome. Unijunction transistor T1 functioning as a relaxation oscillator triggers phase-shift audio oscillator circuit turning it on and off. Capacitor C1 is charged […]