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Strange issue with wall DC adapter - ripple/ground...
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elcrni:
hi all,

I came across a strange thing i can not explain or fix (hobby electronics). I have a sensitive RF receiver, i've been working on it for some time now and it worked beautifully, been receiving and decoding a clean RF signal. I've been using old laptop AC/DC adapter for the whole time.
This morning i've set my receiver in an enclosure and decided i would go with regular 9V 2A wall adapter... then a strange thing happened, my RF reception was all over the place and instead of very clean and regular "blinks" of a LED every time signal goes HIGH (1Hz signal) now i have random and erratic blinks/signal HIGHs...
Then i took another similar dapter, also 9V 1V and everything works like a charm.... then, i've took 5V 4A adapter, removed DC/DC buck converter and again my signal is all over the place...

So in total, i have tried 6 very similar wall adapters, 2 work, 4 does not...

Then a strange thing happens, when i connect the one that does not work, and then take a jumper wire and connect GND of that adapter to the GND of my bench power supply, it works!

Every single adapter that produces chaotic RF signal reception, if i just connect the GND to bench power supply or even to a GND of another adapter, it works.

This led me to believe that there is something wrong with the ground rail on those "faulty" adapter.

I would really appreciate any hints or tips on what am i looking at here and or how to fix it.

Many thanks,
Alek

P.S. This seems very strange to me but could easily be something trivial or common :-)
penfold:
It could be a matter of "common mode" noise, it's quite a big problem with typical wall-warts, normally a bigger problem with more compacted designs which doesn't allow the designer much scope for screening and isolating noise.

A mains-frequency transformer-based adapter may be the best option if you cannot tolerate a permanent earth connection. You could use a common-mode filter or ferrite ring on the power leads, but for the filter to be most effective you would need some earth connection.
elcrni:
Thanks penfold!
not sure i quite understand what the "mains-frequency transformer-based adapter" could be :-)
Also, not sure what one adapter that works has that the one that does not work doesnt have? or this a design difference that i cannot easily solve...

what baffles me is that i have 2 very similar adapter, similar price, size... and one works while the other one doesnt. None of those 2 have a ferrite ring...

Many thanks,
Alek
elcrni:
just reading about isolated and non-isolated adapters... is this what is making issues here?
and if so, is the one working isolated or non-isolated?

many thanks
Alek
G7PSK:
Cheap switch mode power supplies very often have the filter capacitors missing and cause a lot of bother with RF interference to amature radio operators. a fair number of LED lamps do the same.
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