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

"Richard Clark" wrote in message
...
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).

in context of the message i was replying to the writer implied that rf
flowed 'into' the earth and that was the end of it, more correctly it could
be said that rf flows 'through' the earth, but it doesn't dissappear 'into'
the earth.


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:

i have been told before that i have very long trains of thought, usually i
am just trying to be descriptive enough for someone else to follow along...
and i just like ellipsis.


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.

it relates to the common assumption that the radio case, coax shield, and
other items connected to a common 'ground' are at 'rf ground'. ignoring the
'earth', there is also the common misconception that things tied together to
the often discussed 'single point ground' are all 'grounded'... something
that is not necesssarily true when dealing with rf.

On Sun, 12 Nov 2006 19:25:38 -0000, "Dave" wrote:

in context of the message i was replying to the writer implied that rf
flowed 'into' the earth and that was the end of it, more correctly it could
be said that rf flows 'through' the earth, but it doesn't dissappear 'into'
the earth.

Hi Dave,

True, but knowing Bill, I doubt his description was meant to be so
literal as to having current disappear into the earth.

In the sense of RF ground, already described by me earlier, ground is
a pool of infinite charge and as such current into it does disappear.
Otherwise, it would perturb and become less than a ground, its
potential would elevate and that elevation would be in reference to
some other ground.

This is a true picture of the reality of ground as such perturbation
does just this, and is evidenced by local variations of potential to
other "grounds." However, this reduces the discussion to one of
infinite regression and over-qualifies an answer to the primary
question.

i have been told before that i have very long trains of thought, usually i
am just trying to be descriptive enough for someone else to follow along...
and i just like ellipsis.

Up to the ellipsis was fine. The better part of writing is what you
leave behind after you trim off the fat.

it relates to the common assumption that the radio case, coax shield, and
other items connected to a common 'ground' are at 'rf ground'. ignoring the
'earth', there is also the common misconception that things tied together to
the often discussed 'single point ground' are all 'grounded'... something
that is not necesssarily true when dealing with rf.

I can follow the argument for concern, but you really don't offer any
context. There are far more examples of grounding working than not;
and your brush has tarred them all equally.

There is the practical answer to the question of RF ground, and there
is the literal answer (or academic, if you prefer). The practical
answer might have the user elevated hundreds of volts above academic
RF ground. That user might never perceive it in any way because the
user may have contrived to build a virtual ground that satisfies all
the requirements for operating without suffering themselves or any one
else.

73's
Richard Clark, KB7QHC

In article ,
Richard Clark wrote:

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

In other words...... the guy is so full of ****, his eyes are brown.....

ORIGINAL MESSAGE:

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


but rf doesn't flow 'into the earth'

------------ REPLY FOLLOWS ------------

Beware of making broad statements that are supposed to be true in all
cases. The one above is not.

Bill, W6WRT