OXO QRP HF Transmitter

The OXO QRP HF transmitter is a simple, low-power CW (continuous wave) transmitter designed by George Burt, GM3OXX. It is a single-band transmitter that can be built to operate on any of the amateur radio bands from 160 to 20 meters. The transmitter is built around a few standard transistors and a crystal oscillator. It is an elementary circuit to build, and can be assembled from a kit or from scratch.

Fig: OXO QRP HF Transmitter

The OXO transmitter is a QRP HF transmitter, which means that it produces a very low output power. This makes it ideal for making short-range contacts with other amateur radio operators. The OXO transmitter can also be used for experimentation and learning about radio electronics.

OXO QRP HF Transmitter

TL071 Audio Compressor Circuit

The TL071 operational amplifier makes an excellent foundation for DIY audio compressor circuits. This single-supply design TL071 Audio Compressor offers reliable dynamic range control for musical instruments and recording applications.

TL071 Audio Compressor Circuit:

Audio compressor for microphone

This circuit diagram illustrates an audio compressor for microphone signals. Its primary job is to even out the volume of your voice, making soft sounds louder and loud sounds quieter, resulting in a more consistent and professional audio output. This is incredibly useful for podcasts, voice overs, amateur radio, or any application where microphone levels can fluctuate.

Audio compressor for microphone

Getting Started with AIS: Track Ships from Your Shack with a RTL-SDR

The Automatic Identification System (AIS) is a VHF radio-based collision-avoidance protocol that virtually every commercial, passenger, and large recreational vessel in the world is required to carry. Since 2004, the International Maritime Organization (IMO) has mandated AIS transponders on all ships of 300 GT or more engaged in international voyages, all cargo ships of 500 GT or more on domestic routes, and all passenger ships regardless of size.

Every few seconds — sometimes as often as every two seconds when a vessel is manoeuvring — its AIS transponder transmits a compact digital burst on one of two dedicated VHF channels: 161.975 MHz (Channel 87B) and 162.025 MHz (Channel 88B). That burst contains a rich data payload: MMSI number (a unique vessel ID), ship name, call sign, IMO number, vessel type, dimensions, draught, destination, navigational status, GPS position, course over ground, speed over ground, rate of turn, and more.

Getting Started with AIS: Track Ships from Your Shack with a RTL-SDR: