via HACKADAY: Homebrew SDR Ham Radio in 9 Parts

It used to be homebrew ham gear meant something simple. A couple of active devices that could send CW. Maybe a receiver with a VFO. But only the most advanced builders could tackle a wide range SSB transceiver. Today, that goal is still not trivial, but it is way easier due to specialty ICs, ready access to high-speed digital signal processing, and advances in software-defined radio techniques. [Charlie Morris] decided to build an SSB rig that incorporated these technologies and he shared the whole process from design to operation in a series of nine videos. You can see the first one below.

The NE612 is a child of the popular NE602 chip, which contains a Gilbert-cell mixer, and an oscillator that makes building a receiver much easier than it has been in the past. The chips are set up as direct conversion receivers and feed a Teensy which does the digital signal processing on the recovered audio.

One nice thing about the Teensy is that it has an accessory audio board that makes it easy to connect audio inputs and outputs to the device. The DSP does work on the received audio and the transmit audio. There’s also a few other stock parts like an LCD, an encoder, a speaker, a microphone, and things like that. There’s also a digital clock generator (an Si5351), but again all that is common off-the-shelf stuff these days.

The first video is a bit introductory, but by video number two he jumps right into the wiring and why all the circuits work. By the third video, the receiver is actually working and it sounds pretty good. Because the receiver needs I and Q outputs, there are actually two NE612s operating out of phase with each other.

via Blog – Hackaday

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