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Author Topic: Artificial RF Ground?  (Read 1168 times)
Guest

« on: January 12, 2004, 11:15:16 PM »

You guys have been great it suggesting ways to string a random wire from my NYC QTH. Here's another issue: I have attached rig and tuner to a section of 8 gauge copper wire and clamped the other end to a cold water pipe in the bathroom. I have no idea if that copper pipe is really going to ground from my 3rd floor apartment. No one knows.

Question is: How important is it to ground everything? Will one of those Artificial Grounds, like the one made by MFJ do the trick or are we talking about a different kind of ground?

Call is KC2MIM. N0BQF was previous call that expired years and years ago.
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AA4PB
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Posts: 14390




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« Reply #1 on: January 12, 2004, 11:48:43 PM »

Hows the water pipe working?  It is not necessary that it goes into the ground. If the copper pipes in the apartments are all connected together it could make a pretty sizable counterpoise. It is fairly certain that the copper pipes are tied to the AC power ground somewhere in the building in order to meet code.
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Bob  AA4PB
Garrisonville, VA
K5DVW
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« Reply #2 on: January 13, 2004, 08:59:53 AM »

Well, the obvious comment is that it may not be necessary to have a ground connection at all. If you're using a balanced antenna, or an antenna that has it's own grounding scheme (radials, etc) then you just dont need a ground. If you're using some sort of end fed wire, then you might need a ground.

What it boils down to is if your current arrangement works for you and doesnt cause RFI/TVI, dont worry about it.
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KT8K
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« Reply #3 on: January 13, 2004, 12:05:10 PM »

The artificial ground is just a counterpoise with a tuner to resonate it so it presents a nice low impedance for return currents in the antenna system.  Although it is "untuned" (resonant frequency/impedance/etc. unknown)the copper plumbing has the same function.  Save your money on the artificial ground and put it into your antenna(s).  

That takes care of your RF ground, but don't confuse that with your safety and lightning grounds - the other two of the three kinds of grounds.  In your situation the safety ground is your 3rd prong electrical ground, which will protect you in case your equipment develops an internal 120vac short.  That may not do much for lightning, however.  You may not have an optimal solution available for lightning, and the combination of copper plumbing ground and 3rd prong may be all you can do. IF you can, you should bury an 8 foot ground rod and run the biggest possible copper (#6 minimum), in the straightest run possible, up to a commercial lightning arrestor placed in your feedline where it comes into the building.  You might also want to make a coil of coax on the shack side of the lightning arrestor - the choke (inductance) effect will help convince any lightning to take the copper path to ground instead of into your shack.  If you do this, connect all your grounds at a single point to prevent ground loops.  Unless your antenna wire is run close to the ground wire your antenna performance shouldn't be affected, and may be improved by the added counterpoise.  

www.polyphaser.com has a very good discussion of lightning protection and grounding matters in general, if you're interested.
Hope to work you on the air soon. 73 de k8tk - Tim
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WB6BYU
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« Reply #4 on: January 13, 2004, 05:18:39 PM »

The topic of grounds always seems to come up here, as
there is a lot of confusion on the subject.  I suggest
you search back through Elmers on the topic to see some
of the comments.

If you have a counterpose or radial that is close to a
quarter wavelength on the operating frequency, then
there likely is no need for additional grounding.  But
it probably doesn't hurt, either... usually.

Whenever the grounding system is over, say, 1/10
wavelengths, how well it works will be dependent on the
exact operating frequency and the lengths of the
different parts of the ground system.  The "ground wire
tuner" simply tunes out the reactance of the wire, but
it can't make a low impedance path out of a high
impedance wire.

In the end it is really a pragmatic solution:  try it
and see how it works.  If you have problems with RF in
the shack, or  in the neighbor's toaster, see what
happens if you disconnect the wire from the copper pipe.  It certainly won't be a good ground in case of
a lightening strike, but you will have other worries in
that case!
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