Diode ring, just like the linked article. The cool part of the gilbert cell ne602 series (and similar) is its one chip with an oscillator and a mixer and the p

Diode ring, just like the linked article. The cool part of the gilbert cell ne602 series (and similar) is its one chip with an oscillator and a mixer and the performance is barely good enough for 1980s analog cordless phones at 49 mhz with small antennas over a short range. However intermod and strong signal performance is dismal when connected to a large 80M dipole or whatever in some ham radio application. A diode mixer will require some external (IC?) oscillator of course but performance will be vastly better. The "new era" of design as seen in some SDRs seems to be a nice DDS synthesizer driving something like a Tayloe mixer (four very fast analog switches in an IC). I don't have the numbers in front of me but from memory the 3rd order intercept point (higher means less self-generated interference for strong signals) is ridiculously higher for even a cheap analog switch IC as a Tayloe mixer. Of course the power consumption of a DDS and a fast switch will be a little higher (10x? 100x?) than an analog cordless phone chip. There's always tradeoffs.