Board-To-Board Ground Loop Avoidance: Is This Overkill? - Page 1
Forum section: electronics / beginners

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: October 03, 2016, 05:36:22 am
content: I've been designing & prototyping a GPSDO for some time as a learning tool. I'm designing it in modules to be interconnected and trying to avoid ground loop issues since there will be multiple connections per board.So I'm wrapping up the OCXO module now. It consists of a bigIsoTemp 134-10sine wave oscillator, aKO4BB isolation amplifier, and aMiniCircuits RF splitterto send one copy of the signal off to the distribution amplifier and another copy off to the control board (squarer, PLL, etc.).My question is whether I should keep the 1:1 transformers I added to each of the splitter outputs to ensure the two downstream modules don't get a different ground potential on the signal since everything will share power grounds. Or does it even matter? The distribution amp is a single ended input with the shield connected to the chassis/system ground. But the squarer on the PLL board has a transformer input. I have enough gain in the isolation amp to overcome the transformer losses, but are the 1:1 outputs just silly?(Please pardon the ugly board; I haven't cleaned up the silk screen yet.)

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: October 03, 2016, 05:52:00 am
content: In case you're curious, here's some more info on the distribution amplifier I designed & built:http://kb5eo.com/index.php/9-electronics/2-gpsdo-signal-distribution-board

author: German_EE
author_rank: Super Contributor
timestamp: October 03, 2016, 11:51:50 am
content: There are two ways of dealing with ground loops when you are building something modular, both methods are valid but you need to pick one and stick to it.Method One - Everything is GroundEvery PCB has a groundplane on the top surface and this is seam soldered all the way around the case when you mount the PCB. Each connector is soldered to both the groundplane and the case and each module case is either unpainted or connected to the chassis at multiple points. Connections between modules are made using screened cables.Method Two - Single Point GroundingEach PCB is isolated from the case using insulated spacers and there is one and ONLY one connection between the circuit ground and the case, this point is also ground for your power connection(s). All signal connections in and out of the case are made using either balanced circuits which are isolated from ground or opto-isolators.In both cases there is a nice easy rule to follow, a screen isn't a screen if it carries current. Method one does this by making all points at equal potential whilst method two has only one connection to the screened case and therefore no current flows.

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: October 04, 2016, 04:17:43 am
content: Thanks. It seems the "everything is ground" approach works best for this project. Each module will live in a machined aluminum housing and all of them will be screwed to a common plate. I chromate the aluminum so everything is both conductive and corrosion protected.After removing the 1:1 transformers, the board is shorter by 1/4". Good stuff! Going back to my copy of "Noise Reduction Techniques In Electronic Systems" (Henry Ott) for more educational goodness . . .