Re:direct digital converter (Score 1)

Actually I think it is done by way of 4-times oversampling the data, giving you a nice automatically quaderature version of the incoming time-domain signal. It's the way the FlexRadio works, a very fast Taylor detector and commutative switch. If you can sample at 120MHz, you can do the normal 60MHz Nyquist sampling required for the 30MHz HF band, and if you can sample twice as fast, the intervening points will actually be the quaderature phase of the complex spectrum. There's an article about it in Gerald Youngblood's QEX on Software Defined Radios.