On 4/18/2018 1:33 PM, Josh Fiden wrote:
SS30 is an SMPS so a different beast than the prior discussed linear supplies. It's possible that the DC return to chassis connection is needed for EMC compliance. That's providing a low impedance return path for noise generated by switch elements. Without the connection, noise will take an unwanted path and come out as common mode noise.
In fact, the opposite is true. When V- is NOT bonded to shack ground, the power cable forms a transmission line, confining the field for noise current to a small region around the pair. But when V- IS bonded to shack ground, return current divides between the shack ground path and the V- (black) conductor. The fields no longer cancel, the noise current takes whatever path it chooses, and a magnetic loop is formed between V+ and shack ground.
Common mode noise current can easily be blocked using ferrite chokes on the DC cable just was we do with coax.
A frequent source of the noise is capacitive coupling from MOSFETs to chassis, sometimes via a heat sink.
Yes. Interior circuit design and layout is critical to low RF noise. 73, Jim 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 Message delivered to arch...@mail-archive.com
