On 12/13/2010 6:41 AM, John Ragle wrote: > My education needed: why would (in principle) using a Bluetooth > connection to a K3 remove "PC interference?" All the clocks and > clock-generated sharp-edged waveforms will still be present... >
RFI often happens by more than one mechanism. Most RFI is radiated by conductors acting as antennas. Those conductors can be INSIDE the box, AND OUTSIDE the box. Also in general, the longer the wire, the better it is as an antenna at HF. When you reduce the number and length of wires connected to the box, or when you choke them to kill RF current on those wires, you take them out the picture, and are left with radiation from INSIDE the box due to its poor shielding (and poor circuit board layout). This radiated RF is picked up by the ham antenna, so the distances that matter are the distance between the noise source (computer) and that antenna. For example -- many laptops will radiate trash, especially on some of the higher HF bands via their power cable. If you remove the power cable and run them on battery, the trash sometimes goes away (or gets weaker). Nothing you can do with external cables will kill radiation from wiring inside the box, so when you choke the cables, that radiation will still be there (but weaker, because the antenna is shorter). RF trash can also be CONDUCTED via Pin One Problems in both ham gear and computers when they are interconnected. Pin One Problems put RF onto so-called "ground" contacts (for example, inside the computer at the serial or USB port), and Pin One Problems couple RF from an improper shield connection into the radio. For this mechanism, no antenna action is involved -- the RF is conducted on the cable shield because the shield is not properly connected on both ends. For a tutorial on the Pin One Problem, and how to deal with RFI, see http://audiosystemsgroup.com/publish.htm and http://audiosystemsgroup.com/RFI-Ham.pdf Another common coupling mechanism for RF trash is Pin One problems in TV sets and other consumer electronics putting that trash onto the shields of cables (like the CATV cable), where it is then radiated by the CATV system. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
