0
\$\begingroup\$

I have to pass a couple of analog signals between separately grounded systems over a HPDB68 cable. Ground loops have been a major issue previously, so the signals are passed differentially and recovered against target ground using a differential amplifier. The shield is connected to ground on one side. On the other side, I'd connect it to the PCB ground using a capacitor to short RF but break LF loop.

What bothers me is: what is the common way to do it with the D-Sub connector on metal enclosure? Those connectors are usually screwed right on, which does not allow for the capacitor. Making custom spacer for isolation is doable, but this has to be a common issue? There have to be some off-the-shelf parts and solutions for this? Yet I can neither find nor remember ever seeing such an example?

\$\endgroup\$
3
  • 1
    \$\begingroup\$ Most commonly, the connector shells are connected to ground. However, there's no requirement the cable shield be connected to all shells, ergo, no ground loop. That said, for shock safety, it's important that no device have a "hot" chassis, but that does not require using the cable shield. \$\endgroup\$ – DrMoishe Pippik Mar 10 at 21:19
  • \$\begingroup\$ I've seen all kinds of hack connection jobs inside D-shaped connector shells. None have looked 'good', seeming l like an afterthought (and there's never enough room to put it all back together). I expect that the solution is typically applied inside the gadget, where the shield is passed though an unused pin of the D-connector, and AC (or hybrid) coupled to GND on the PCB. I'll be following... \$\endgroup\$ – Chris Knudsen Mar 10 at 21:20
  • \$\begingroup\$ You are mixing up between PS "common" and "ground". It is does not must to be connected together. Ground means connect to earth potential , reduce of influence of EMF. power supply can be isolated. \$\endgroup\$ – user263983 Mar 10 at 21:26
0
\$\begingroup\$

Use a spacer (or just drill it out and make a bigger hole), as long as it's insulate enough it should work. There will be a small amount of capacitance between the chassis and the dsub. You might be able to find a standard standoff that is made from nylon or something like that if you are also concerned about standoffs connecting to the channel

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.