On 10/18/2013 11:45 PM, Bill Frantz wrote:
When I tried measuring in the negative lead, I found zero amps. The problem is that the grounding system in my station setup bypasses the negative lead, probably in several ways, letting me power the K3 up with no connection to the negative power supply lead at all.
That suggests that the negative terminal is bonded to the chassis in your DC power supply. There are some good reasons to NOT do that, and many power supplies are built with DC- not bonded to the chassis. It also suggests that all the gear in your station is properly bonded together.
With all equipment bonded together, one might think that the bonding could carry DC-, and no "black wire" was needed. That's wrong -- while DC follows Ohm's Law, AC current (and RF) finds the path of lowest impedance, which includes the loop inductance of a path. So if there were no black wire, RF would couple into the resulting loop, putting it on the red wire.
What we fail to realize is that parallel wire cable (like the red/black glorified zip cord we use for power, and that is sold as speaker cable) is a sitting duck for RF. Far better to use twisted pair, which has about 30 dB better RF rejection. I've fixed a lot of RFI to audio system problems by replacing that zip cord with twisted pair.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
