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 Post subject: A Good ground
PostPosted: May Mon 14, 2012 8:41 pm 
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Hey guys, I know this has probably been discussed a million times, but what would be a good sub for ground, anything connected to the wall?

Jon


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 Post subject: Re: A Good ground
PostPosted: May Mon 14, 2012 8:48 pm 
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Wow.... no easy answer! We need to know what you are trying to ground.

Is this an antenna ground, to improve reception? Or, are you concerned
about a safety ground for stray AC voltages?

Pete


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 Post subject: Re: A Good ground
PostPosted: May Mon 14, 2012 8:49 pm 
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The best ground would be a stout wire taking the shortest path possible to a copper bround rod or two driven at least 3 feet into the ground. You can pour a bucket of water around the rods before critical DX'ing. Next best, a copper water pipe. Least reliable and safe is anything having to do with the wall socket, although if you are using a 3 wire plug for safety reasons, you already have this connection.


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 Post subject: Re: A Good ground
PostPosted: May Mon 14, 2012 9:10 pm 
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A "ground" can be defined as any connection (to the local earth reference), that is "good enough" for the purpose.

Examples:
Safety--3-wire cord wherein the outer structure of something is tied back to the building supply ground---the path could be 50 feet or more, and it would still be safe. It would however probably be a **really bad** RF ground

High-frequency RF--eg a ~100Mhz transmitter or receiver with a single-ended antenna. This requires a really short path to ground--one that will have negligible impedance relative to the impedance of the antenna circuit.

And lots of things in between.....

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 Post subject: Re: A Good ground
PostPosted: May Mon 14, 2012 9:51 pm 
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This question is in regard to the grounding needed for the older sets when turned on for use, Without the three prong type plug. Could you tell me more about the grounding area on the wall outlet and how safe it is to use. I am on the second story so I will not be able to drive a stake into the ground. thanks

Jon


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 Post subject: Re: A Good ground
PostPosted: May Mon 14, 2012 10:08 pm 
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Location: Gainesville, Florida
you should be able to find a simple AC outlet tester at your local hardware store electrical section like Lowes for instance. if you are good with a meter there is another way teasting AC to ground and neutral. they should be the same reading. if the socket tests OK then there should be a good neutral and ground at the outlet. the receptical box should have a screw in the center that is grounded. that should be a good ground. some danger involved but ground just the same. be careful :shock:

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 Post subject: Re: A Good ground
PostPosted: May Mon 14, 2012 10:13 pm 
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Speaking of which, are there any GFI devices other than wall recepticles that can be inbedded in sets? I researched this years ago when I was thinking about a dangerous amplifier designs, and considered using relays to make break connections for faulty wall sockets. I now think relays may be slower than Dr. House's paddles.


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 Post subject: Re: A Good ground
PostPosted: May Mon 14, 2012 10:14 pm 
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Relying on a ground rod or earth return for any sort of RF grounding is
folly. You will end up losing 50% of the signal in earth losses. A good
RF ground is best provided by a counterpoise ground plane system
that is referenced above lossy earth returns.

At 100 MHz a simple wire countepoise is infinitely better than trying
to use a ground rod or earth return. You can get away with shortcuts
on receiving apps, but wasting 50% of your transmitting power on
heating earthworms is sheer folly. Again, without knowing the exact
application for the question it is hard to give a technically sound
answer.

Pete k1zjh


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 Post subject: Re: A Good ground
PostPosted: May Tue 15, 2012 5:34 pm 
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Im thinking that earth ground is return circuit for radio station transmitters ? maybe you could tell us how to build a reasonable ground plane for this application. as part of the thought if Im not mistaken an example would be a car as a gound plane for its radio receivers as it has no earth unless you are dragging an anchor :shock:

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 Post subject: Re: A Good ground
PostPosted: May Tue 15, 2012 6:00 pm 
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ketron281989 wrote:
This question is in regard to the grounding needed for the older sets when turned on for use, Without the three prong type plug. Could you tell me more about the grounding area on the wall outlet and how safe it is to use. I am on the second story so I will not be able to drive a stake into the ground.
The center screw holding the plastic plate is electrically connected to the neutral in any 3 prong outlets (the "ground prong receptical").

If you attach a wire to that point it will be "grounded" for AC power purposes. Just make sure there is no way for it to come lose and fall across a live AC power plug.

Curtis Eickerman

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 Post subject: Re: A Good ground
PostPosted: May Tue 15, 2012 6:48 pm 
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Eickerman wrote:
ketron281989 wrote:
This question is in regard to the grounding needed for the older sets when turned on for use, Without the three prong type plug. Could you tell me more about the grounding area on the wall outlet and how safe it is to use. I am on the second story so I will not be able to drive a stake into the ground.
The center screw holding the plastic plate is electrically connected to the neutral in any 3 prong outlets (the "ground prong receptical").

If you attach a wire to that point it will be "grounded" for AC power purposes. Just make sure there is no way for it to come lose and fall across a live AC power plug.

Curtis Eickerman


Sometimes, always, or never, dependswhere you live and how old the house. C'mon you know better.


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 Post subject: Re: A Good ground
PostPosted: May Tue 15, 2012 7:35 pm 
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codefox wrote:
Sometimes, always, or never, dependswhere you live and how old the house. C'mon you know better.
The center screw is connected to the frame of the outlet which is also the bare wire (if it is connected). House wiring is subject to testing that is true.

In that regard I have found 220 wired to 110 VAC outlets. Something like this might be a good investment.
Attachment:
AC-Tester.JPG
AC-Tester.JPG [ 11.7 KiB | Viewed 443 times ]
Curtis Eickerman

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 Post subject: Re: A Good ground
PostPosted: May Thu 17, 2012 4:44 pm 
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tubeAMP wrote:
Im thinking that earth ground is return circuit for radio station transmitters ? maybe you could tell us how to build a reasonable ground plane for this application. as part of the thought if Im not mistaken an example would be a car as a gound plane for its radio receivers as it has no earth unless you are dragging an anchor :shock:



In general, it makes little difference for receivers, but for transmitter
antenna counterpoise the last thing you'd want is a ground rod. Earth
is very lossy, and having half of the RF current flowing into lossy
earth and keeping earthworms warm isn't a very efficent use of RF energy.

The best ground is a series of radials laid on the earth surface,
laid out like the spokes of a wheel. Burying the radials increases
the losses, with the depth becoming more critical as the frequency
is increased. Essentially you want a ground plane that is highly
conductive below the radiator--in effect it serves as the other half
of a dipole element for a single wire antenna. Many broadcast
stations followed the RCA standard and use 120 1/4-wave
radials below each vertical radiator.

A car body can serve as the missing "half" of the antenna; but it
isn't very efficient below VHF. Besides at HF, you'd be using a very
electrically short antenna that has low radiation resistance and
high ohmic losses.

Unfortunately the term "Ground" is often used synomously for
RF, lightning/static dissipation and AC safety concerns--that's
why some clarity as to what the poster is trying to accomplish
is helpful in these instances.

http://www.k0bg.com/ground.html

Pete

http://www.antennasbyn6lf.com/design_of ... d_systems/
http://www.chem.hawaii.edu/uham/radials.html


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 Post subject: Re: A Good ground
PostPosted: May Thu 17, 2012 5:31 pm 
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Location: Gainesville, Florida
hey Curtis that tester is exactly what I had in mind. it will tell you everything you need to know about the AC receptacle. at least then you would know if there is a good ground or not. for a receiver that is. I assumed receiver but the post was non specific as pointed out by the lessons from Pete.
a 'receiver' antenna ground can be obtained at the house electrical outlet after a few simple tests assuring that there is a ground. there that should do it :shock:

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