DIY Antennas, QRP, SDR & Ham Radio Projects from VU3DXR
A collection of fundamental electronic circuits designed for amateur radio and RF experimentation. Explore detailed schematics for VFOs, power amplifiers, band-pass filters, and voltage regulators. These resources provide the essential building blocks for homebrew projects, focusing on circuit stability, impedance matching, and practical bench-testing techniques
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 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.
Simple Crystal tester – The idea for this crystal tester circuit sprung out of the need of testing a large number of oscillator crystals lying unused in a big hobby box. testing the crystals one by one without the appropriate device would have been very slow and a time consuming task. Commercial crystal testers are […]
Here is another qrp cw transmitter pulled out from SPRAT back issues, which is simple to build with commonly available components from every one shack. We can subsititute 2N2222 for BC108 and BD139 for BD 131.
This is a clever Battery low power indicator circuit designed by G3AGX that provides a visual indication when equipment is drawing power, even at very low current levels. The circuit is particularly useful for monitoring standby power consumption or confirming that equipment is actually powered on. Battery Low Power Indicator Circuit Analysis The heart of […]
Simple zener diode tester Ever found yourself with a handful of zener diodes, wondering if they’re still good or what their actual breakdown voltage is? Zener diodes are incredibly useful components for voltage regulation, but sometimes, their markings can be ambiguous, or you just need to quickly verify their functionality. That’s where a simple zener […]
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 […]
Manufacturers of electronic equipment use LCDs for calculators, watches, mini-videogames, and pagers, for example. In comparison with LED-based displays,which consume power on the order of tens of milliwatts, an LCD consumes only a few microwatts. The LCD thus saves power by a factor of approximately 1000. Checking an LED is as simple as checking a […]
This white led torch circuit provides an effective solution for powering white LEDs. It is ideal for flashlights, emergency lighting, and various other applications. The circuit operates efficiently from one or two primary cell batteries. The core of the circuit involves a transistor (Q1) and a tapped inductor, forming a blocking oscillator. When the power […]
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 […]