An SDR Transceiver The Old-School Way

Software-defined radio stations or SDRs provide a change in the way we use radio. From your FM radio, which most likely already has one-chip SDR technology built into a chip, to general-purpose SDR singing and general-purpose dancing, which you’d find on an experimenter’s bench, signal processing control has shifted from the analog domain to digital. The possibilities are endless and some of the old ways of building a radio now seem outdated.

[Pete Juliano N6QW] has been an expert in home brewing radio for a very long time and has proven that there are many opportunities for old-fashioned home brewing radio in SDR with his RADIG project. This is an SDR transceiver for HF that does all the quadrature splitting and mixing work with home-made modules, not the more common technique for hiding it in an SDR chip. This is a very long reading in diary format from the bottom up and the remarkable thing is that it went from an idea to a working SPT in about three weeks.

Block diagram of N6QW SDR
Block diagram of N6QW SDR

So what’s in the home letter revision? Both RF preamplifiers, filters and PA are conventional, as you would expect, switching between relay transmission and reception. A common signal transmission and reception path is split in two and fed to a pair of ADE-1 mixers, where they are mixed with quadrature local oscillatory signals to obtain I and Q, which are fed to (or from the transmission case). ) on the StarTech sound card. The local oscillator is a Si5351 synthesizer chip in the form of a USB-powered SDR-Kits module, and the 90-degree phased quadrature signals are generated with a set of 74AC74 flip-flops as a separator.

The show’s launch was a Raspberry Pi running Quisk, and although he mentioned using Teensy to control the Si5351 at the beginning of his diary, photos from the latest radio show that Pi took the job. It is clear that this is a very experimental radio, as it stands with wired modules on a wooden board, so we look forward to any improvements. It has a design feel that can eventually be built by many other radio amateurs, so it’s fascinating to be in the beginning.

If Q and I let you gasp when it comes to SDR technology, maybe we can help.

thanks [Bill Meara N2CQR] for the top!