On Sat, 11 Nov 2006 12:06:16 -0000, "David" nospam@nospam wrote:

What would you define RF ground as? There seem to be a lot of different
ideas.

Hi David,

This is another instance of scale matters. Ground is meant to imply
an infinite resource of charge with no impedance to its flow.

Of course, "infinite" and "no impedance" are factors that are the
first casualties when RF is added as a requirment. This is from the
simple consequence of scale, because distance causes phase shifts and
brings impedance. A long wire that is perfectly capable as a ground
lead for 60 Hz can become a liability to short wavelength RF. That
wire (that we call ground) may connect to an infinite resource of
charge (the proper ground), but that charge can't get to the other end
because of possibly infinite impedances [again, infinite is in the eye
of the creator].

If you can contrive to make that lead to ground half a wavelength long
to the RF of your interest, that wire ceases to offer impedance and
acts much as you would demand of a ground wire. Curiosly enough, it
will never be zero impedance because it qualifies as a radiator (the
paradox of ground) which adds the loss of radiation. For most
purposes, however, it may be your only choice and you live with it.

Now, when we get to the actual mud of ground, and how well it performs
as an infinite resource of charge, RF still brings problems of scale
because that mud will also exhibit impedances correlated to wavelength
(corrected for velocity factors) that disconnect it from the total
earth's resource for infinite charge. This is why you lay down
radials (which simply increases coverage, but never completely escapes
the scale of wavelenght problem).

Moral to this tale:
Put your source (transmitter) as close to the mud as possible;
lay out as much copper as you can from that point to suit
a broader range of frequencies.

Alternative moral:
Put your source (transmitter) as far from the mud as possible;
Use a dipole and insure there are no connections to ground
whatever. Any violation of this last rule brings grief.
Such violations are legion and few escape.

73's
Richard Clark, KB7QHC

Alternative moral:
Put your source (transmitter) as far from the mud as possible;
Use a dipole and insure there are no connections to ground
whatever. Any violation of this last rule brings grief.
Such violations are legion and few escape.



Hi Rich

This knocked the gerbil off his wheel

so if i am doing the above, do you mean, no coaxl shield to ground or
did you really really mean not even a ground to my rig chassies?
i understand the dipole is ballanced at that point and the antenna
dosn't need a gnd (plane) radial (min is a center feed equal l)


so i would just have a rig and antenna nothing else??

(presume my electrical gnd is ok on the aka 3prong plug)

Hi Myles,

Let's just cut to the chase with some selective editing:

On Sun, 12 Nov 2006 16:14:21 GMT, ml wrote:

Any violation of this last rule brings grief.
Such violations are legion and few escape.

(presume my electrical gnd is ok on the aka 3prong plug)

B I N G O !

You have won the traditional violation of the rule. This is the
meaning of "legion," there are many, many, many such examples. Those
who violate this rule are often blindsided by other violations along
the way.

What is the third prong of the 3 prong plug for? Most would say
ground (and be blindsided to the complete term being "safety" ground).
The 3rd prong is not designed to be current carrying in the
conventional sense, only in the safety sense when the neutral wire or
hot wire becomes exposed to the device user (basically forcing a short
circuit that then opens through a blown fuse).

So, you have TWO paths to ground:
1. Through neutral;
2. through safety ground.

The question becomes:
"What is the quality of it being RF ground?"
Answer:
"Neither 1 nor 2 above were ever considered
in those terms. Hence the quality of their being
RF ground is unknown and the presumption of being
poor examples is a reasonable expectation."

The next question becomes:
"Why do I need their ground proximity?"
Answer:
"You don't - unless...."

Unless
1. You are powering off the Mains;
2. Powering off battery that is being recharged off the Mains.

Both numbers 1 & 2 are a frequent blindside to those attempting to
isolate ground loops.

73's
Richard Clark, KB7QHC

the real fooling part is somthing kinda simple, can be sooo tricky

In article ,
Richard Clark wrote:

Hi Myles,

Let's just cut to the chase with some selective editing:

On Sun, 12 Nov 2006 16:14:21 GMT, ml wrote:

Any violation of this last rule brings grief.
Such violations are legion and few escape.

(presume my electrical gnd is ok on the aka 3prong plug)

B I N G O !

You have won the traditional violation of the rule. This is the
meaning of "legion," there are many, many, many such examples. Those
who violate this rule are often blindsided by other violations along
the way.

What is the third prong of the 3 prong plug for? Most would say
ground (and be blindsided to the complete term being "safety" ground).
The 3rd prong is not designed to be current carrying in the
conventional sense, only in the safety sense when the neutral wire or
hot wire becomes exposed to the device user (basically forcing a short
circuit that then opens through a blown fuse).

So, you have TWO paths to ground:
1. Through neutral;
2. through safety ground.

The question becomes:
"What is the quality of it being RF ground?"
Answer:
"Neither 1 nor 2 above were ever considered
in those terms. Hence the quality of their being
RF ground is unknown and the presumption of being
poor examples is a reasonable expectation."

The next question becomes:
"Why do I need their ground proximity?"
Answer:
"You don't - unless...."

Unless
1. You are powering off the Mains;
2. Powering off battery that is being recharged off the Mains.

Both numbers 1 & 2 are a frequent blindside to those attempting to
isolate ground loops.

73's
Richard Clark, KB7QHC

An RF ground is where RF energy flows into the earth. A lot of folks
misuse the word "ground" when they really mean a common connection
point, which may or may not have anything to do with earth. Be careful
to define just what you mean.

Bill, W6WRT


------------ ORIGINAL MESSAGE ------------

On Sat, 11 Nov 2006 12:06:16 -0000, "David" nospam@nospam wrote:

What would you define RF ground as? There seem to be a lot of different
ideas.

but rf doesn't flow 'into the earth'. rf current is always trying to
complete the circuit back to it's source... i.e. 'ground radials' under a
vertical are collecting the current and returning it to the feedpoint, so
they are actually 'sucking' rf out of the ground. the 'ground' connection
to a radio feeding a dipole is actually returning current from the ground
back to the feedpoint via the outside of the coax shield... that is why you
can get high voltages at the radio end of the cable, if too much current is
coupled from the antenna onto other conductors connected to 'ground' they
will feed current back through the radio 'ground' and out the shield of the
feedline to get to the feedpoint, and if you happen to be too close to the
antenna or some other object that couples the rf to you then you get burned
when the rf from you flows back to the radio when you touch something that
is 'grounded'.


"Bill Turner" wrote in message
...
An RF ground is where RF energy flows into the earth. A lot of folks
misuse the word "ground" when they really mean a common connection
point, which may or may not have anything to do with earth. Be careful
to define just what you mean.

Bill, W6WRT


------------ ORIGINAL MESSAGE ------------

On Sat, 11 Nov 2006 12:06:16 -0000, "David" nospam@nospam wrote:

What would you define RF ground as? There seem to be a lot of different
ideas.

Dave wrote:
but rf doesn't flow 'into the earth'. rf current is always trying to
complete the circuit back to it's source... i.e. 'ground radials' under a
vertical are collecting the current and returning it to the feedpoint, so
they are actually 'sucking' rf out of the ground. the 'ground' connection
to a radio feeding a dipole is actually returning current from the ground
back to the feedpoint via the outside of the coax shield... that is why you
can get high voltages at the radio end of the cable, if too much current is
coupled from the antenna onto other conductors connected to 'ground' they
will feed current back through the radio 'ground' and out the shield of the
feedline to get to the feedpoint, and if you happen to be too close to the
antenna or some other object that couples the rf to you then you get burned
when the rf from you flows back to the radio when you touch something that
is 'grounded'.


"Bill Turner" wrote in message
...
An RF ground is where RF energy flows into the earth. A lot of folks
misuse the word "ground" when they really mean a common connection
point, which may or may not have anything to do with earth. Be careful
to define just what you mean.

Bill, W6WRT


------------ ORIGINAL MESSAGE ------------

On Sat, 11 Nov 2006 12:06:16 -0000, "David" nospam@nospam wrote:

What would you define RF ground as? There seem to be a lot of different
ideas.




Correct. If pink fairies dance the head of the pin, all bets are off.
Although everything applies if dancing blue fairies...

JS

"John Smith" wrote
the 'ground' connection to a radio feeding a dipole is actually
returning current from the ground back to the feedpoint via the
outside of the coax shield.
______________

Usually there are good reasons to connect an earth-based tx chassis to an
earth r-f ground. But if the tx is feeding a dipole or other balanced
radiator, that radiator doesn't need or use a connection to an earth r-f
ground to generate its radiation. The current source for one side of the
dipole is the other side of the dipole.

For example consider airborne VHF tx/rx/antenna systems -- which work just
fine with no reference to an earth "r-f ground," whatsoever.

RF

Richard Fry wrote:
"John Smith" wrote
the 'ground' connection to a radio feeding a dipole is actually
returning current from the ground back to the feedpoint via the
outside of the coax shield.
______________

Usually there are good reasons to connect an earth-based tx chassis to
an earth r-f ground. But if the tx is feeding a dipole or other
balanced radiator, that radiator doesn't need or use a connection to an
earth r-f ground to generate its radiation. The current source for one
side of the dipole is the other side of the dipole.

For example consider airborne VHF tx/rx/antenna systems -- which work
just fine with no reference to an earth "r-f ground," whatsoever.

RF

Richard:

I have been "short" with some because I suspect they "pull my leg" a
bit. I have no problem with the example you cite. However, if someone
is at the point where they really need to ask, better for them to be
overly cautious and "overly grounded." It would bother me is someone
was injured or worse from some oversight of mine, something I was not
clear enough on. And yes, I realize that even attempting to avoid such
errors, I may make them.

So, we agree...

JS

On Sun, 12 Nov 2006 15:14:49 -0000, "Dave" wrote:

but rf doesn't flow 'into the earth'.

Hi Dave,

That statement is contradiction to the following:

'ground radials' ... are ... 'sucking' rf out of the ground.

It necessarily follows that RF does flow "into" the earth by your own
admission of it coming out (by whatever means).

the 'ground' connection
to a radio feeding a dipole is actually returning current from the ground
back to the feedpoint via the outside of the coax shield...

Very true. However, the ellipsis (...) elongates a 25 word statement
into an 118 word run-on sentence:

that is why you
can get high voltages at the radio end of the cable, if too much current is
coupled from the antenna onto other conductors connected to 'ground' they
will feed current back through the radio 'ground' and out the shield of the
feedline to get to the feedpoint, and if you happen to be too close to the
antenna or some other object that couples the rf to you then you get burned
when the rf from you flows back to the radio when you touch something that
is 'grounded'.

If I try to parse the intent of this, it becomes a string of
assertions held in suspension until the summary that ties them
together. That never happens. The conclusion:
then you get burned
when the rf from you flows back to the radio when you touch something that
is 'grounded'.
bears no relation to the matter of currents in the earth - except as a
consequence to rather perverse conditions.

73's
Richard Clark, KB7QHC