Comment Re:Computer Not Required (Score 1) 177
I/Q interfaces are vulnerable to ground loops only if the I/Q interface is analog. Why should it be, when we have excellent digital interfaces designed specifically for stereo digital audio? There are now several inexpensive SDRs (price range $100-$200) with USB interfaces, e.g., the Funcube Dongle Pro+ and the SDRPlay (there's now a second version). There's also the ultra-cheap RTL-SDR, but its narrow 8-bit A/D limits its use to VHF or UHF signals without strong adjacent channel interference. It's ideal for ADS-B (with a filter!) but I wouldn't recommend it for HF.
I've done most of my work so far with the Funcube dongle, which samples at 192 kHz and 16 bits/channel, feeding a USB interface. It looks just like a standard audio A/D to the OS, because that's what it is. The I&Q signals are produced at baseband so yes there are DC offsets and small gain and phase errors, but I found them easy to remove in software. Some phase noise is sometimes audible within a few hundred hertz of DC, but is easily swamped by typical input noise and gain settings.
Overall, this thing makes an excellent but inexpensive general coverage receiver. I sure wish I had something like this when I was a young ham without much money.