Circuit Ideas on VU3DXR.in collect practical, buildable circuits for amateur radio and general electronics, grouped into Audio, Transmitter, Receiver, Power and Other support circuits. Use this page as a hub to explore proven designs with schematics, measurements and notes from real shack use, then adapt them to your own station or lab projects.
Audio Circuits
LM386 Audio Oscillator
Simple LM386‑based audio oscillator that generates stable test tones for checking audio paths, alignment of filters and measuring gain in receivers or microphone chains, ideal for bench testing without complex or expensive equipment.
SSM2167 Microphone Preamplifier with Compression for uBITX HF Transceiver
Compact SSM2167 preamplifier with built‑in compression designed to lift low speech levels, increase average talk power and maintain clean audio on uBITX and similar HF QRP rigs used in crowded band conditions and DX work.
Simple Mic Compressor Using 3 Transistors
Minimalist three‑transistor microphone compressor that evens out voice dynamics, boosts soft speech and gently limits peaks, giving more consistent and punchy audio into SSB transmitters without needing ICs or complicated circuitry.
SSM2167 Audio Processor for Baofeng Mic Enclosure
Drop‑in SSM2167 audio processor board sized for common Baofeng mic shells, adding preamp gain, compression and basic noise reduction to handheld radios so your local repeater and simplex audio sounds clearer and more professional.
Really Cheap Audio Compressor
Low‑cost audio compressor using only easily available parts, intended for homebrew HF or FM rigs where the operator wants stronger average modulation, better readability and automatic control of wide speech‑level variations without DSP.
Amateur Radio – Mike Preamplifier / Speech Compressors / Audio Processors – Resources
A curated collection of microphone preamp, speech compressor and audio processor ideas, schematics and external resources, serving as a central reference for hams planning to experiment with advanced transmit audio processing chains.
LM324 Microphone Speech Compressor
Speech compressor built around the LM324 quad op‑amp, offering adjustable gain and compression ratio, suitable for integration between microphone and HF rig to keep audio level steady without audible pumping or harsh distortion artifacts.
NE555 Based Microphone Amplifier
Unusual but effective microphone preamplifier using the NE555 in a linear configuration, giving good gain for dynamic or electret microphones and showing how the classic timer IC can double as a simple, low‑cost audio building block.
Simple Audio Compressor for SSB HF Radio Rigs
Audio compressor tailored specifically for SSB HF operation, designed to raise average talk power, protect against over‑driving the rig and maintain clear, natural speech during weak‑signal contacts, nets and crowded contest situations.
Dynamic Speech Compressor with Audio Preamplifier
Combined microphone preamp and dynamic speech‑compressor module that increases effective transmit power, evens out voice level changes and adds on‑board gain control, simplifying integration into existing homebrew transceivers and audio boxes.
Microphone Compressor Using Two Transistors
Very compact two‑transistor compressor stage providing gentle level control, ideal where board space is tight but you still want more consistent microphone audio, improved intelligibility and protection against sudden loud bursts on air.
Noise Cancelling Condenser Microphone
Condenser microphone wiring and circuitry arranged for noise‑cancelling operation, reducing background shack noise, fans and traffic so that your transmitted audio remains focused on your voice even in noisy or portable operating environments.
Dual Microphone Noise Cancellation Using LF351 Op Amp
Two‑microphone noise‑cancellation circuit using an LF351 op‑amp to subtract ambient sounds and preserve desired speech, illustrating classic feed‑forward noise‑control techniques that can be added in front of many radio microphones or interfaces.
Condenser Mic Audio Amplifier: DIY Guide
Dedicated audio amplifier for condenser microphones providing correct biasing, gain and low‑noise operation, aimed at hams wanting to adapt studio‑style microphones to HF transceivers, QRP rigs or PC‑based SDR and streaming setups.
Microphone Compressor Using LM1458
Microphone compressor design using the LM1458 dual op‑amp to achieve controllable compression with straightforward components, suitable for inclusion in external audio boxes or directly inside homebrew HF radio enclosures and head units.
Audio Compressor for Microphone
General‑purpose microphone compressor circuit aimed at improving intelligibility and average loudness for any speech application, from amateur radio to basic PA systems, using affordable parts and easily understood gain and threshold adjustments.
TL071 Audio Compressor Circuit
Single‑op‑amp compressor built around the TL071, demonstrating how a low‑noise JFET input op‑amp can produce smooth gain control for microphones with minimal external components and without needing special or expensive compressor ICs.
NJM4558 Audio Compressor Circuit: Complete Schematic & Build Guide
Dual‑op‑amp NJM4558 compressor circuit presented with full schematic, component explanation and performance notes, suitable for homebrewers who want a reliable, repeatable audio dynamics processor for their station microphone or podcast setup.
TL081 Speech Processor for HF Rigs
Speech processor using the TL081 op‑amp to increase effective SSB talk power, sharpen articulation and maintain controlled peaks, making HF contacts more readable especially during marginal propagation, noisy bands or contest pileups.
Microphone Preamplifier with Audio Peak Limiter
Microphone preamplifier combined with an audio peak‑limiter stage designed to stop over‑driving the transmitter, helping keep ALC under control while still delivering strong, consistent audio on HF, VHF or UHF equipment in everyday use.
Audio Clipper Circuit Using BC547 and 1N914 Diodes
Simple transistor and diode‑based audio clipper that trims extreme peaks before the transmitter, useful as a safety stage in front of older rigs or linear amplifiers that are sensitive to over‑modulation and sudden audio overshoot.
Log Audio Compressor Circuit for Smooth Natural Compression
Log‑response audio compressor that follows signal level in a more ear‑friendly way, maintaining natural‑sounding speech while still increasing average modulation and protecting against aggressive clipping or excessive hard limiting.
Pink Noise Generator Circuit Using 741 Op-Amps
Pink‑noise generator using classic 741 op‑amps, providing a useful test source for audio equalization, loudspeaker checks and room response measurements, and a good exercise in shaping white noise into a 1/f spectral distribution.
Build a Simple Speech Processor Circuit Using LM358
Speech processor based on LM358 that increases average voice level and articulation for QRP and HF rigs, built with common components so experimenters can tune compression strength and tonal balance to their personal preference.
VK3YE’s AGC Circuit for uBITX
Audio‑path AGC add‑on for the uBITX HF transceiver, inspired by VK3YE’s design, which automatically controls receive audio level, reduces listening fatigue and shows how simple AGC can be added to modest homebrew or kit transceivers.
Transmitter Circuits
Circuits – Short Wave Transmitter
Simple shortwave transmitter for basic HF experimentation, intended as an entry‑level RF project that demonstrates oscillators, buffering and output stages while remaining buildable with common components and modest workshop tools.
Circuits – 7 MHz CW / AM QRP Transmitter
Dual‑mode 7 MHz QRP transmitter capable of CW and low‑level AM, providing a flexible platform for learning HF transmitter design, on‑air operating and simple antenna matching with a single compact and efficient circuit board.
Circuits – 7 MHz 5 Watts CW Transmitter
7 MHz CW transmitter delivering around 5 W output, suitable for local ragchews and DX when bands cooperate, showing how to scale a simple QRP design up to higher power while retaining stability and straightforward construction.
Circuits – Pippin QRP Transmitter
Classic Pippin‑style HF QRP transmitter presented as a reproducible design, ideal for builders who want a proven minimalist CW rig that still offers respectable performance and an approachable parts list for Indian homebrewers.
Circuits – 40M TAG QRP Transmitter
40 m TAG‑style QRP transmitter optimized for simple components and easy alignment, giving newcomers a gentle introduction to HF RF stages, keying and low‑power operation on one of the most popular amateur bands.
G4RAW 80M QRP TAG CW Transmitter
80 m CW TAG transmitter based on G4RAW’s concept, adapted and documented for homebrew builders who want a robust low‑band rig for NVIS, regional contacts or late‑night operating with a modest antenna and power supply.
OXO QRP HF Transmitter
Compact OXO‑type HF QRP transmitter showcasing a simple but effective architecture, suitable for portable operation, experimental antennas and learning how oscillator, buffer and PA stages interact in a small CW transmitter.
Simple Series Modulated AM QRP HF Transmitter
Series‑modulated AM HF transmitter designed for QRP‑level power, illustrating classic high‑level modulation techniques and producing pleasant‑sounding AM for local nets, demonstrations or vintage‑style broadcast experiments.
Simple Two Stage One Watt AM Transmitter
Two‑stage 1 W AM transmitter using general‑purpose transistors, ideal as a first RF transmitter project for beginners who want audible results on MW or lower HF with relatively few parts and straightforward construction steps.
Class C – AM Transmitter
Efficient Class‑C RF power amplifier stage for AM service, demonstrating how high‑efficiency non‑linear PAs are built, biased and loaded, and how they fit into a larger transmitter chain with appropriate modulation arrangements.
Series Modulated AM Transmitter
AM transmitter using series modulation to inject audio directly into the RF power rail, providing a clear example of this architecture and giving homebrewers a route to strong, clean AM with comparatively simple circuitry.
Build Your Own Micro Power AM Transmitter
Micro‑power AM beacon‑style transmitter intended for short‑range coverage and experimentation, allowing hobbyists to explore AM broadcasting techniques, antenna coupling and propagation without needing high power or large equipment.
Simple CW Transmitter Using the 74HC240 Buffer IC
CW transmitter built around a 74HC240 logic buffer IC, showing how digital parts can be repurposed as RF building blocks and offering a fun, educational project for experimenters with surplus logic chips and basic test gear.
Build Your Own Simple Sine Wave Oscillator
Basic sine‑wave RF oscillator that can serve as an exciter, test source or VFO, demonstrating feedback, amplitude control and stability considerations in a straightforward circuit that is easy to tweak and re‑frequency.
DIY AM Transmitter Circuit with IRF510 MOSFET
IRF510‑based AM transmitter for MW/HF that uses a common MOSFET power device, giving builders a clear example of MOSFET RF operation, heat management and matching to small antennas for enjoyable, low‑power local AM use.
Mini FM Radio Transmitter
Small FM broadcast‑band transmitter suitable for short‑range audio links, experiments and demonstrations, showing how to modulate, stabilize and radiate an FM signal using a compact set of parts assembled on a simple PCB.
Build Your Own 40M AM Transmitter: A Classic Radio Project
Complete 7 MHz AM transmitter project that walks through circuit blocks, component choices and construction hints, ideal for hams who want a dedicated 40 m AM rig for nets, experiments and classic‑style operating.
Build Your Own Grenade AM Transmitter Circuit
Compact “grenade”‑style AM transmitter that concentrates respectable power into a small package, illustrating portable AM design and requiring careful attention to layout, filtering and heat for reliable field operation.
Build Your Own 80M CW Transmitter from Scratch
Discrete‑component 80 m CW transmitter built from scratch, aimed at builders who want to understand each stage in detail and enjoy reliable low‑band CW contacts using a rig they fully constructed and debugged themselves.
Build a Simple FM Band Transmitter Circuit
General‑purpose FM band transmitter providing a clear example of oscillator, modulation and antenna coupling, suitable for campus radio, audio links or lab demonstrations when used within appropriate local regulations.
Build Your Own 90 MHz Crystal Controlled FM Transmitter
Crystal‑locked 90 MHz FM transmitter that trades some flexibility for excellent frequency stability, showcasing how to combine crystal oscillators, buffer amplifiers and simple modulators for clean local FM transmission.
80 Meter 1W QRP Transmitter with Ceramic Resonator Control
1 W 80 m QRP transmitter controlled by a ceramic resonator, offering a compact and economical way to get on the low bands while retaining reasonable stability and a very approachable, repeatable circuit layout.
Simple FM Transmitter Using BC547 Transistors
Discrete FM transmitter using common BC547 transistors, designed for beginners who want to see an entire RF chain built from inexpensive small‑signal devices and experiment with modulation, range and antenna placement.
Build a Simple 40 Metre CW Transmitter Using 2N2222
40 m CW transmitter built around the ubiquitous 2N2222 transistor, making it an ideal first HF project, easy to source parts for and simple to troubleshoot with basic test instruments and on‑air reports.
How to Build a 3-Watt AM Radio Transmitter
3 W AM radio transmitter suitable for strong local coverage, teaching how to handle higher RF currents, heat and filtering while staying within a home workshop skill level and using realistic, affordable components.
DIY 3-Transistor FM Bug Transmitter Using Piezo Mic
Tiny three‑transistor FM bug transmitter that uses a piezo microphone element and minimal components, primarily an educational project to explore RF oscillation and modulation in a very compact, low‑power form factor.
Build a Miniature FM Transmitter – DIY Electronics Project
Miniature FM transmitter that demonstrates how far component count and size can be pushed down while still getting usable range, making it a fun challenge build and useful test source for nearby radios.
DIY 1 MHz AM Transmitter: A Perfect Weekend Project for Beginners
Beginner‑friendly 1 MHz AM transmitter project designed as a weekend build, teaching core RF concepts while remaining forgiving about layout, making it suitable for students, newcomers and casual experimenters.
27 MHz AM Transmitter Circuit for Hobbyists
27 MHz AM transmitter for hobby use, useful as a lab project or low‑range communications tool, highlighting antenna matching at 11 m and the behaviour of small RF power stages in this popular CB‑like band.
Tiny FM Transmitter with Just a Few Easy-to-Find Components
Very small FM transmitter using only a handful of common components, ideal as a quick build for beginners or a starting point for experimenting with audio pre‑emphasis, filtering and layout optimisation.
The Poor-Man’s Transmitter: Building a Simple AM Radio Beacon from Vintage Electronics
Simple AM beacon‑style transmitter constructed from salvaged vintage parts, perfect for learning how to reuse old electronics while creating a practical RF signal source for propagation checks and antenna experiments.
Build Your Own Commando AM Transmitter
Higher‑power AM transmitter variant that delivers strong local signals and requires more attention to heat, filtering and power supply design, offering a satisfying project for builders wanting more than QRP‑level output.
Circuits – Sovina2 40M Class E Transmitter
Class‑E 40 m transmitter design focusing on high efficiency and compact circuitry, giving homebrewers a chance to explore modern switching PA techniques that run cool and achieve impressive power from modest supply voltages.
Ten Minute QRP Transmitter
Rapid‑build QRP transmitter project that can be assembled in a very short time, ideal for demonstrations, workshops or beginners who want quick on‑air success without a long, complex construction process.
Building Steve Quest’s Simple AM Transmitter
AM transmitter based on Steve Quest’s simple, well‑known design, adapted and documented for VU3DXR readers with practical build tips, component options and notes on getting stable, clean audio onto the air.
Receiver and RF Front-End Circuits
MAX2633 Based VHF Preamplifier for Entire VHF Band
Low‑noise VHF preamplifier covering a wide section of the band, built around the MAX2633, useful ahead of scanners or SDRs to improve weak‑signal reception while keeping noise figure and intermodulation under good control.
Circuit – FM Bandstop Filter for RTL SDR
Passive FM broadcast bandstop filter designed to sit in front of RTL‑SDR receivers, attenuating strong local FM broadcast signals so that weaker HF, VHF or utility signals are not crushed by front‑end overload.
VHF Radio Receiver Antenna Amplifier Using MAX2633
Simple VHF LNA using the MAX2633, intended as an antenna‑mounted preamp for improved reception of repeaters, satellites or weak simplex stations, with emphasis on low noise and straightforward construction.
Simple DIY Active Antenna for Crystal-Clear Reception
Wideband active antenna front‑end that boosts weak HF and VHF signals, ideal for space‑limited setups, SDR users and experimenters who want good general‑coverage reception from a short whip or compact outdoor element.
Simple Signal Grabber Circuit for Shortwave Reception
Signal grabber circuit that allows sharing a transmitting antenna with multiple receivers or SDRs without upsetting tuning, giving a safe and convenient way to monitor HF activity while still using the main station antenna.
Signal Booster Enhancing RF Performance of Radio Receiver
RF signal booster that raises weak incoming signals before the receiver front end, helping overcome feedline or splitter losses and making marginal stations more readable, with attention to gain and noise figure balance.
Active AM Band Antenna for Better Reception
Tuned active antenna designed specifically for the MW broadcast band, giving improved AM reception in noisy or indoor environments where simple long wires struggle, especially when combined with small portable receivers or SDRs.
Simple Receiver S-Meter Circuit for Your Radio
Add‑on S‑meter driver circuit that converts receiver AGC or audio level into a readable meter indication, allowing older or simpler radios to gain a useful signal‑strength display for operating and signal comparison.
AM Radio into an SSB Receiver with a Simple BFO Circuit
Simple BFO add‑on that turns an ordinary AM broadcast radio into a basic SSB and CW receiver, demonstrating clever reuse of existing sets and the importance of beat frequency oscillators in communications receivers.
Simple DIY Active Antenna: Boost Weak HF/VHF Signals
Broad‑coverage active antenna that boosts both HF and VHF signals for SDRs and communications receivers, giving a single compact solution for monitoring multiple bands when space or budget prevents using full‑size antennas.
The Simple RF Indicator: A DIY Tool for Detecting RF Signals
Very simple RF indicator probe that lights or indicates when RF is present near a test point, handy for debugging transmitters, oscillators and feedlines without needing a full spectrum analyser or power meter.
A Classic Active Antenna for 0.5–30 MHz
Classic active antenna design covering roughly 0.5–30 MHz, offering good sensitivity and compact size, ideal for HF listening posts, SDR monitoring setups and situations where long wire antennas are impractical.
Build Your Own Solar Powered Radio
Solar‑powered radio project that combines RF circuitry with a small photovoltaic power system, demonstrating how to create a self‑contained receiver useful for emergency kits, field listening or educational demonstrations.
Power and Battery Circuits
Circuits – Battery Low Power Indicator
Battery low‑power indicator circuit that provides a clear visual warning when supply voltage drops below a set point, protecting portable transceivers, handhelds or test gear from operating in undervoltage conditions.
DIY Lithium-Ion Solar Charger for 2-Cell Batteries
Solar charger for 2‑cell lithium‑ion packs, designed for field and portable stations, showing how to safely manage charging, protection and panel sizing so that QRP rigs and accessories stay powered off‑grid.
Automatic Battery Saver Circuit: Prevent Battery Drain
Automatic battery saver circuit that disconnects or reduces load when idle, preventing deep discharge of portable station batteries and extending runtime, useful for beacon projects, remotes and low‑duty‑cycle devices.
Test, Tools and Other Circuits
Circuits – Check Digital or Linear Circuits with the Flick of a Switch
Test circuit that helps determine whether a circuit node behaves in a digital or linear way, giving experimenters a quick diagnostic tool when dealing with mixed‑signal boards or unknown sections in salvaged equipment.
Circuits – Dark Room Timer
Dark‑room timer circuit that generates accurate, repeatable timing intervals with a pleasant tone, and which can also serve as a general purpose delay or countdown timer in the workshop or other hobby projects.
Circuits – White LED Torch
White LED torch circuit focusing on efficient drive and simple construction, suitable for everyday use in the shack, emergency lighting or as a convenient example of LED current‑limiting and battery management basics.
Circuits – Simple Tester Checks LCDs
Simple LCD tester circuit that lets you quickly verify segment operation and detect faulty displays, useful when repairing equipment, prototyping projects with surplus displays or sorting harvested LCD modules.
Circuits – Offset Tuning Indicator for CW
Offset‑tuning indicator that gives a visual cue when CW tone is at the desired audio pitch, helping operators net precisely on frequency and making operation with simple rigs or older receivers more comfortable.
DIY – Making Printed Circuit Boards
Step‑by‑step guide to making printed circuit boards at home using simple materials and methods, covering artwork, etching and drilling so homebrewers can turn prototype circuits into robust, repeatable PCBs.
Circuits – Simple Zener Diode Tester
Zener diode tester that allows quick checking of zener voltage and basic behaviour, very handy when sorting through mixed parts or confirming that salvaged components still meet their original specifications.
Circuits – Simple Crystal Tester
Simple crystal tester circuit that confirms whether RF crystals oscillate and roughly where, helping builders avoid chasing faults caused by dud frequency control components in transmitters or oscillators.
Audible Continuity Tester for Electronics Testing
Audible continuity tester with a clear sounder so you can keep eyes on the PCB while probing, ideal for wiring checks, PCB debugging and quick validation of home‑etched boards or complex harnesses.
Ham Radio Repeater Toneburst Module Circuit
Toneburst module for repeaters that generates the required burst tone for access on certain European‑style systems, showing how to integrate simple tone generation into handheld or mobile station setups.
Building a Crystal-Controlled CMOS Oscillator: A Classic Circuit for Precise Timing
Crystal‑controlled CMOS oscillator that provides accurate timing or reference signals, illustrating how to build stable oscillators from basic logic components and use them in RF or digital timing applications.
Building a Classic Untuned Field Strength Meter
Classic untuned RF field‑strength meter that gives a relative indication of nearby RF fields, invaluable for antenna tuning, leakage checks and general RF experimentation around the shack or garden.
Incandescent Lamp Flasher Using IRF510 HexFET
Incandescent lamp flasher using an IRF510 HexFET as the power switch, demonstrating basic power MOSFET drive and timing while creating a practical, visible indicator or decorative flasher.
Simple Incandescent Lamp Flasher Circuit Using 7555 Timer
Lamp flasher built around the low‑power CMOS 7555 timer, suitable for battery‑powered projects and as a demonstration of astable timer configuration, duty‑cycle adjustment and load driving with basic components.
Build a DIY Ion Detector: Detect Airborne Ions and Electrostatic Emissions
DIY ion detector that senses airborne ions and electrostatic emissions, providing an interesting science project and a way to explore electrostatic phenomena beyond typical radio‑frequency experiments.
Simple UJT Crystal Checker Circuit: Test Your Crystals Like a Pro
Crystal checker using a UJT that lets you quickly test crystals for activity and approximate operation, handy for sorting surplus parts and ensuring frequency‑control components are healthy before building transmitters.
Simple UJT Morse Code Practice Oscillator Circuit
Morse code practice oscillator based on a UJT that generates a clean, pleasant audio tone for CW practice, ideal for learners and as a compact practice keyer that runs from simple batteries.
Build Your Own Hidden Transmitter Hunter RF Sniffer Circuit
RF sniffer circuit intended for hidden‑transmitter hunts and general RF exploration, giving a simple, handheld indicator of RF presence for direction‑finding games and interference‑hunting exercises.
NanoVNA Test Jig: A Practical Guide for Accurate RF Measurements
NanoVNA test jig that makes measurements more repeatable and accurate by standardising how components are connected, helping users get reliable data from their low‑cost VNAs on antennas, filters and RF devices.
Building an FT8 Digital Interface – Dive into Digital Modes
Audio and keying interface for FT8 and other digital modes that isolates the radio from the computer sound card, reduces hum and level issues and forms a solid foundation for exploring modern weak‑signal digital communications.
