On Jul 2, 9:33 am, John Smith wrote:
K7ITM wrote:
...
The only way to keep a wire--e.g., piece of coax--from being a
radiator is to keep net current at zero. If there's no net current,
you didn't need the wire anyway (at that frequency, at least). If
it's a protective ground for mains frequency, it will probably still
work for that purpose if you add ferrite for RF choking.

K7ITM:

I was hoping the rf/dc/ac could reach ground via a very low
resistance/impedance to rf on the inner surface of the braid and the
center conductor ...

While it would be virtually impossible to reduce rf on the outer braid
to absolute zero, I was hoping the choke would provide sufficient
impedance to rf to where it became near negligible, at least for
practical purposes.

Regards,
JS

If there's a net RF current, there's a net RF current, and it will
radiate. It matters not a whit whether you say the net is on the
inside or the outside or distributed between them in any proportion.
If you choke things so there's no net current, you may as well not
have bothered putting the wire/coax/whatever in to begin with.
Consider what the current on the inside of the outer conductor must be
if the coax is acting as a transmission line, and consider where that
current goes at the "top" end of the piece you suggest.

To keep RF "out of the shack," put a Faraday cage around the shack and
don't turn RF loose inside that cage. Then it doesn't matter (with
respect to RF "in the shack") whether the Faraday cage is connected to
"ground" or not.

What exactly is "ground," anyway? Do you think it has magical
properties? What ARE its properties? What does it do for you?

K7ITM wrote:

...
If there's a net RF current, there's a net RF current, and it will
radiate. It matters not a whit whether you say the net is on the
inside or the outside or distributed between them in any proportion.
...

Really, then I can throw away the current choke on my coax to my 1/2
wave vertical then? I THINK NOT!!! And, I DON'T think there is rf on
the outside of the coax shield--I DO think there is on the inside of the
braid ...

...
What exactly is "ground," anyway? Do you think it has magical
properties? What ARE its properties? What does it do for you?

Find an improperly grounded kw xmitter/liner whose case is hot with rf
and running into a noticeable SWR, now touch a sharp corner of the case
with your finger. Pay attention to the hissing noise(s), the flesh
being vaporized into a white smoke, the characteristic white, deep
penetrating, slow-to-heal rf burn(s) on your finger, etc.

Now ground the case and touch the sharp corner--notice the lack of pain?

Now, that you should get you started with what a ground is ... got
anymore questions?

Now, I can explain all that without having to bring magic into the
argument--but hell, go ahead, give me your "magical" version if you
would like ...

Regards,
JS

On Jul 2, 3:07 pm, John Smith wrote:
K7ITM wrote:
...
If there's a net RF current, there's a net RF current, and it will
radiate. It matters not a whit whether you say the net is on the
inside or the outside or distributed between them in any proportion.
...

Really, then I can throw away the current choke on my coax to my 1/2
wave vertical then? I THINK NOT!!! And, I DON'T think there is rf on
the outside of the coax shield--I DO think there is on the inside of the
braid ...

....which is balanced by the RF on the center conductor. If it doesn't
radiate, there's no net current; the center conductor current is equal
in magnitude and opposite in phase to the current on the adjacent
inside of the outer conductor. Why would you think that what you
quoted above would imply that you could get rid of the choke on your
transmission line, if you want to keep the line from having a net
current and therefore radiating? It says just the opposite. But of
course, you already knew that, didn't you? Sorry, rhetorical
question.

K7ITM wrote:

...
...which is balanced by the RF on the center conductor. If it doesn't
radiate, there's no net current; the center conductor current is equal
in magnitude and opposite in phase to the current on the adjacent
inside of the outer conductor. Why would you think that what you
quoted above would imply that you could get rid of the choke on your
transmission line, if you want to keep the line from having a net
current and therefore radiating? It says just the opposite. But of
course, you already knew that, didn't you? Sorry, rhetorical
question.

Actually, it took me awhile to put this together, your picture of "the
ground" given in your text ...

Basically, we are two blind men, you have the trunk of the elephant in
hand, me the foot ... but now that I think about it, I remember what
picture the trunk brought to my mind ...

A radiating ground I have used before, my first exposure to one instance
of it was like this:

In college, living in a couple of rooms rented to me by an individual
having a home near the campus, I resided on the third floor of an old
victorian (and, keep in mind, building codes were rather sparse back
then.) The plumbing had been "reworked" and sections of it replaced
with pvc. The old steam radiators had, had their piping removed in the
basement level. In despiration, I had to resort to a wire ran around
the base boards of the rooms and "adjusted" for various freqs/bands.
This ground DID, indeed, radiate. Indeed, the "fuzz" on the video
signal of the tv sets proved this absolutely--at times. The am band on
a radio was also, frequently, troubled by my signals/rfi.

All the above, because the owner did not want "wires ran about."

The "ground wire" I was proposing would attempt to function as a
transmission line, and simply carry the signals to a suitable ground;
Whether you made that a legitimate number of buried radials of suitable
length, a wire ran above ground and through the bushes, a wire
connecting a few ground rods, or a run to the pipe in the basement,
etc., would be at the users discretion ... however, the "ground wire"
would be made to NOT radiate, or radiate as little as possible ... that
is "the ground" (but actually, a "grounding transmission line") I was
proposing with the coax.

Regards,
JS

K7ITM wrote:


If there's a net RF current, there's a net RF current, and it will
radiate. It matters not a whit whether you say the net is on the
inside or the outside or distributed between them in any proportion.
If you choke things so there's no net current, you may as well not
have bothered putting the wire/coax/whatever in to begin with.
Consider what the current on the inside of the outer conductor must be
if the coax is acting as a transmission line, and consider where that
current goes at the "top" end of the piece you suggest.

To keep RF "out of the shack," put a Faraday cage around the shack and
don't turn RF loose inside that cage. Then it doesn't matter (with
respect to RF "in the shack") whether the Faraday cage is connected to
"ground" or not.

What exactly is "ground," anyway? Do you think it has magical
properties? What ARE its properties? What does it do for you?

Interesting ... suggesting that if an inductance/capacitance it added
into the shield (or center conductor) and in series with such, so that
the current voltages between the center conductor and braid are 90
degrees lagging/leading that a net current would be possible between the
inside braid and the center conductor. But, still due to the choke on
the outer braid--impossible there (well, vastly reduced.)

Hmmm ... a name for it? Perhaps "Tuned Ground" or "Tunable Ground." grin

Regards,
JS

John Smith wrote:
...
the current voltages between the center conductor and braid are 90
degrees lagging/leading that a net current would be possible between the
...

In the above, 90 = 180 ... just caught that ...

JS