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Station Ground and a Noise Sink

22 May

And nary the twain should meet. Ive been looking at improving my station ground for some time. This becomes more important with the anxiety generated by locally large electrical storms and my mental state when retiring for the evening. That is to say I may forget to remove my feedline at the service entrance to my shack. Ive been rudely awakened at 0230 L time more than once and found myself dashing off to unplug my radios and other equipment.

There are safety grounds and then there are other grounds. First, I am no authority on grounding. However, I want to learn about this subject. Recent articles in QST and on some selected web sites are  much more adept at explaining the single point safety ground than I would ever hope to be….try the QST archives and perhaps W8JI web. I have no real safety ground hence my interest. When fooling around with grounds be sure to follow your country codes and always follow best practice.

On a second note, I have spent many hours reducing station received noise. When I began, my station received noise was in excess of S-9 in SSB (2.4 Khz) bandwidths. Since noise power is proportional to received bandwidth I have taken to measuring my received noise in my widest AM mode which is currently AM (9.0 Khz). My recently measured noise level is running at S-3 to S-4 on 20 Meters in wide AM mode. A lot of improvement since my days of S-9. Most of this improvement is due to the liberal application of ferrite materials throughout my home and station cabling. I used and applied Doctor Counselman’s white paper link you will find filed under “Good Stuff” just to the right on my Blog Page. With my little pistol signal it has allowed me to work loads of things that I would not have been able to hear under normal circumstances. Yet my quest continues. And here is where I get into fuzzy thinking- but just a little.

Safety Grounds are high surge current but mostly DC grounds. There are whole text books written on this subject. I need a safety ground and I know it. However,  I am also interested in a low impedance AC ground that will effectively shunt unwanted RF to infinity. Sort of an infinite RF sink that I can throw unwanted signals into and have them go away. My Elmer tells me this is hard to do and so I really need to try this for myself. I have the instruments to make the measure so I will try it. The reason for this exercise is that I want to try to see if I can quiet devices like DSL Modems etc. When I had my internet DSL modem in my shack I had tons of ferrite on every lead-good HF ferrite like Mix 31 and still I could hear DSL noise -0nly lightly- but it was still present. There are all sorts of sources like DSL modems in a modern home and so I am searching for a low cost solutionto: how do you quiet a noise source if ferrite does not do the entire job?

This line of thought all began when I happened across Dr. Bingo’s website. He proposed  a buried 12 foot long dipole of 12 gauge wire to be used as a dummy load. You can find that article here:

http://www.km5kg.com/dummy.htm

After reading that article and knowing my Elmer had used a really large sheet of copper foil in his attic as a low impedance to infinity under his attic mounted tuner I thought to myself, what if we combine both ideas and see if we get a low impedance to ground over a broad range of frequencies? Then I would have two things-a dummy load that works well and a low impedance RF ground.

So today or over the weekend I intend to construct an aluminum foil dipole that will lay on my kitchen flooring just above my foundation slab. I will try various layouts like typical dipole, right angled dipole etc. My goal is to get a low impedance (1-15 ohms) to infinity. Successful or not I will publish my result here in graphical form along with my wife wondering what I am doing with a floor full of her aluminum foil on the floor!

Even if successful with this endeavor, I may have found a solution that cannot be implemented because I still would need to place the foil or connect to it and that would require a large low impedance foil strap connector-not a high inductance wire. In the AC or RF world nothing is simple. Ground changes with frequency-or at least grounds properties change. Moisture will move things around a lot. I dont know if this idea has merit or not.  But this is the essence of learning so I will plow ahead. I learn better by doing rather than reading. The important thing is to measure results not guess at them. I will be using my AIM 4170 Vector Impedance Meter to collect data.

I still need to do a safety ground-how did I ever get off on this tangent?

Thanks for reading my Blog. Best, Chas W7MAP/5

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Posted by on May 22, 2009 in Radio

 

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