Anyone care to help with grounding?

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Re: Anyone care to help with grounding?

Postby radiostationx » Tue Feb 25, 2020 10:26 pm

Suggestion Dave, mark up the ground point and switches

Image

Your efhw 80-10 has 49:1 matching unit, I dont know the Al value of their tranny core but I chose a manganese material with an Al of 885 to make this very similar one on the right but with PTFE coated wire windings and resin potted.
The one on left , same design but smaller core/ matchbox style for qrp ops.

Image

Very good results with no ground,tested at 50w CW but will do 100w easy.
I reckon you will be fine without a ground on your efhw 80-10 but try it out with/without gnd.
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Wed Feb 26, 2020 3:42 pm

If nothing changes, i'm going with diagram pictured, will add the extras depending on how it plays.
The electrician has now bonded my new rod to the supply, just waiting some time and the weather to complete it all.

http://testsite.davekearley.co.uk/wp-content/uploads/Proposed-Mk4.png
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Thu Feb 27, 2020 3:57 pm

Managed to get the coax cables bonded and grounded, now we have the first problem - when the rig is connected to PC via CAT, i get a high pitched noise, about 1khz maybe.
Obviously a loop of some sort, the path would be rig>cat>pc>ground>coax>rig. Disconnecting the power to the rig makes no difference so its not psu noise/loop definitely coax/cat loop.
A picture of current status below.

http://testsite.davekearley.co.uk/wp-content/uploads/humming.png


EDIT
It seems that the loop is via the CAT ground connection and the audio to the PC, disconnecting the PC audio-in stops the noise. No idea if that helps.
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Re: Anyone care to help with grounding?

Postby radiostationx » Thu Feb 27, 2020 8:15 pm

I put a symbol on the drawing near the star ground point, this indicates chassis ground not electrical earth which has a different symbol.

I think there is likely some leakage to chassis ground possibly across the usb cable, could be a multitude of things, immunity issue with ac psu on pc or pc clock.

For the SDR..Have you got an airspy or sdrplay ?
You can use spectrum spy or the sdrpaly spectrum by steve andrew to ident the freq causing issue.
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Thu Feb 27, 2020 8:45 pm

Its an SDR Play.

It looks like the issue might be my Digimode cable, it's supposed to be fully isolated but on testing with a meter I can see that all the grounds are connected so USB, CAT and audio in/out grounds are connected, this is wrong as far as i can see as it lists full galvanic isolation and has transformers on the audio lines so the grounds should all be separated.
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Re: Anyone care to help with grounding?

Postby radiostationx » Thu Feb 27, 2020 8:52 pm

On the cable usb side, has it got 4 wires - + and a data pair plus an unshielded/uncovered wire( drain wire) running through it connected to usb plug shell ? (chassis gnd)

At radio end, is there a bare drain wire there as well on body of connector ? (chassis gnd)

PS Some things that seem bad can have a positive outcome. You are conducting practical real world experiments on your own station which is great Dave because you will already have gained much knowledge before your exam :thumbup:
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Thu Feb 27, 2020 9:59 pm

I'll have to check the shields/drians etc.

But, it does not matter if the USB plug is pulled - the loop seems to be from the CAT sleeve and the PC audio-in connection - as soon as the CAT plug goes in or I touch the sleeve to rig chassis, the noise starts, even with USB out.

There is a clear bridge between the CAT ground and the audio ground - this is badly wrong as the digimode is sold as fully galvanically isolated which is clearly wrong here as that, to me at least, would indicate no connection at all between rig-side and pc-side.


And yes, its all learning, i'm enjoying looking at things and working out current/loop paths etc, I'm certain I'll get to the bottom as well ;)
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Re: Anyone care to help with grounding?

Postby radiostationx » Thu Feb 27, 2020 10:14 pm

Could be the CAT cable itself (poor joints or a break in the drain wire) or breakdown/short of the transformer.

Reason I went initially for USB was becasue 90% of chinese made usb cables and motherboard header sockets are utter crap especially mixed with digital audio/radio applications they cause more problems than anything else in a set up.
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Thu Feb 27, 2020 10:43 pm

Ok,ta

I should get a reply from the maker tomorrow, i'll be doing some more tests on this cable too.
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Re: Anyone care to help with grounding?

Postby G4RMT » Thu Feb 27, 2020 10:58 pm

I'd not thought much about this before, because it never used to be this complicated, but it does strike me that now the mains electricity rules have leaked into our RF systems, the damn situation is stupidly complex. Worse still, where would you find an electrician with Part P certification who understands ANYTHING about RF. The idea of an upstairs grounding system, and the possibility of RF getting into the system and causing havoc would be a nightmare. I'm left wondering if this extra grounding is actually necessary. I wonder if it's just possible to have an RF grounding system and isolate this from the mains side of the installation. Clearly difficult to stop the chassis of a mains powered radio being connected to electrical earth, but maybe with a bit off effort and planning?

I used to work in quite a few studio installations where there was a mains earth but a separate technical earth - how on earth this would fare nowadays I don't know.
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