Total posts : 45366
Ken speaks the truth about the RF hash inside a computer case. I will defer to his experience re A/D conversion for audio but I can relate mine for scientific A/D. I use a PCI card A/D 12 bit system for temperature measurement/control and the best performance, limited by digital hash, is noise equivalent to .025 degrees C in a system with about this resolution. This is good but there are frequent noise spikes ten times this amount, especially with disc activity, which cause problems in a closed loop control system.
Back to part 15 stuff, I have several p15 devices perched on a shelf above my work area, including a rain gauge and an outdoor thermometer. On occasion the displays blank due to signal loss (temporary interference) so I tolerate this. I added a PIR driveway alert system and the problem became worse with very frequent “black outs”. Missing the obvious, I replace the batteries in the units but there was no improvement. I eventually saw through the trees that the new driveway alert receiver was, by inference, radiating a signal which interfered with the other receivers. This is probably due to a super-regen receiver and relocating this receiver about 10 feet away solved the problem. The lesson is that even receivers can, and usually do, radiate RF and are subject to p15 regulations.
This driveway alert system bears no FCC identification and, though it works, it appears that these are being dumped on the market at a very low price ($13) perhaps to clear inventory before someone at the FCC notices.
Neil
