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I'm currently experiencing what I think is induced coupling on my ground line. Can someone explain how this is possible?

I live on the third floor of an apartment block and my only grounding option is currently the third prong of an ac outlet. I was under the impression that any low freq noise on the ground line would dissipate into the earth, however this is not what I'm experiencing. Any idea why?

I'm thinking perhaps there is some resistance on the ground-line and some rf and ac is taking a shorter path to my shack, instead of taking the longer route to the utility ground. I think this is happening because my apartment building doesn't have a ground rod in place and relies on the the utility companies ground, which is earthed who knows where.

I have an amp connected to my receiving radio and the utility ground I'm using at the moment is creating audible hum. I figure if I can use a quieter ground then this will improve the fidelity of any audio I want to amplify. Most of the interference is at 50hz (UK), which I guess is being conducted on the ground-line from my some of my neighbors apartments, although there's a lot from various other frequencies too. I plan on using some grounded coaxial cable connected to a rod outside with the intention of shielding any rf's from my hopefully quiet ground.

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    $\begingroup$ Could you provide a description, photo, or diagram of your ground system and what's connected to it? Since we're working with RF, physical layout matters. $\endgroup$
    – Kevin Reid AG6YO ♦
    Commented Jun 1, 2015 at 20:44
  • $\begingroup$ There isn't really such thing as "dissipate in earth". Current flows in a circuit. If you have significant impedance in your circuit, expect voltage to appear. If you want a useful answer, do please provide more information. $\endgroup$
    – AndrejaKo
    Commented Jun 2, 2015 at 8:42
  • $\begingroup$ I live on the third floor of an appartment block and my only grounding option is currently the third prong of an ac outlet. I'm experiencing lots of noise on the line and am wondering how that's possible. I'm thinking perhaps there is some resistance on the groundline and some rf an ac is taking a shorter path to my shack, instead of taking the longer route to the utility ground. I thnk this is happening becuase my appartment building doesn't have a ground rod in place and relys on the the utility companies ground, which is earthed who knows where. $\endgroup$
    – SIRT
    Commented Jun 2, 2015 at 15:02
  • $\begingroup$ Please edit your question to include requested information instead of putting it in comments. I've taken care of that for you here. $\endgroup$
    – Kevin Reid AG6YO ♦
    Commented Jun 2, 2015 at 21:50
  • $\begingroup$ Hi, a few more questions: What equipment / circuit are you grounding? Why is it grounded, what are you expecting from the ground? What do you mean by Low Frequency? 7 MHz? 1 kHz? 50 Hz? That'll help us answer. $\endgroup$
    – tomnexus
    Commented Jun 5, 2015 at 15:38

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This sounds like a basic ground loop problem. Make sure you don't have multiple paths to ground. Grounding every single piece of equipment, and the antenna sounds like it might be a good and safe idea but is not really good practice. Try several methods of consolidating your grounding method.

We probably need more details but I would guess if you're in the 3rd floor of an apartment you're antenna is probably not outside, or it's at least not outside while you are not operating. In this scenario my guess is that you really don't need a ground for lightning or RF reasons. The electrical ground that's part of the third prong on your electrical cord is probably sufficient. If your receiver doesn't use any high voltages it may not even need the electrical ground. You could try bypassing that and just use the Amp ground and bond the chassis grounds together.
A basic guide to grounding can be found all over the internet. Here's the ARRL version: http://www.arrl.org/grounding

I should also add that you should use common sense and I take no responsibility if something goes wrong since I do not know your whole setup I may be missing something crucial that would have changed this advice.
KISS (Keep It Simple Stupid!) Something a professor told me constantly.

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