Author Topic: Board-To-Board Ground Loop Avoidance: Is This Overkill?  (Read 2299 times)

0 Members and 1 Guest are viewing this topic.

Offline Melt-O-TronicTopic starter

  • Frequent Contributor
  • **
  • Posts: 259
  • Country: us
  • Brilliant with a slaughtering iron in my hand!
Board-To-Board Ground Loop Avoidance: Is This Overkill?
« on: October 03, 2016, 05:36:22 am »
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 big IsoTemp 134-10 sine wave oscillator, a KO4BB isolation amplifier, and a MiniCircuits RF splitter to 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.)
« Last Edit: October 03, 2016, 05:42:52 am by Melt-O-Tronic »
 

Offline Melt-O-TronicTopic starter

  • Frequent Contributor
  • **
  • Posts: 259
  • Country: us
  • Brilliant with a slaughtering iron in my hand!
Re: Board-To-Board Ground Loop Avoidance: Is This Overkill?
« Reply #1 on: October 03, 2016, 05:52:00 am »
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

 

Offline German_EE

  • Super Contributor
  • ***
  • Posts: 2399
  • Country: de
Re: Board-To-Board Ground Loop Avoidance: Is This Overkill?
« Reply #2 on: October 03, 2016, 11:51:50 am »
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 Ground
Every 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 Grounding
Each 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.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 
The following users thanked this post: Melt-O-Tronic

Offline Melt-O-TronicTopic starter

  • Frequent Contributor
  • **
  • Posts: 259
  • Country: us
  • Brilliant with a slaughtering iron in my hand!
Re: Board-To-Board Ground Loop Avoidance: Is This Overkill?
« Reply #3 on: October 04, 2016, 04:17:43 am »
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 . . .
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf