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

"David" nospam@nospam wrote in :

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

Except in the case of ground-mounted antennas, there is really no such
thing. There is RF neutral, though.


--
Dave Oldridge+
ICQ 1800667

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

A good "r-f ground" has a very small impedance to the flow of r-f current at
the frequency of interest.

A good r-f ground is especially important when using a ground-mounted
vertical monopole radiator, because the path to "ground" is in series with
the r-f current flowing on the monopole. Power consumed by the ground
system is wasted (not radiated as EM energy).

At medium wave broadcast frequencies and in the 160 meter and low HF bands,
a system of ~120 buried radials each about 1/4-wave long provides a
reasonably low-Z ground connection -- probably 2 ohms or less, regardless of
the ground conductivity at the site. This was determined experimentally by
Brown, Lewis and Epstein of RCA in 1937.

Copper water pipes in the home, and even buried ground rods typically are
not good, low-Z r-f grounds.

But many antenna types - such as a dipole - do not need or use such an r-f
ground for efficient radiation.

RF

"David" nospam@nospam wrote in message
...
What would you define RF ground as? There seem to be a lot of different
ideas.


1. One needs to define properties or "regular" ground.

2. Illuminate it with RF of particular frequency and particular antenna.

3. Study the effect of 1 on 2 and you will get some idea. Amount of
reflection or absorption would be the indicator of how good "RF ground" it
is.

As far as suitability of "ground" to "work" with antennas it is somewhere
from horrible (rocky ground) to "perfect" (sea water, copper mine, etc.)

Other than that, if you can walk or swim on/in it and you expose it to RF,
then I suppose you could call it RF ground.
If there is no RF, the RF ground disappears :-)

Somethinglikethat?!?

73 Yuri, K3BU
da salt water muddy RF ground lover
join the Tesla Sparks at N2EE www.TeslaRadio.org

rf ground is where ever you connect your meter/scope/analyzer ground lead.

"David" nospam@nospam wrote in message
...
What would you define RF ground as? There seem to be a lot of different
ideas.

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



David:

Ground can be a relative thing. What I have always found to be good
advice is that EVERY ground, at some point, be allowed to reach a low
ohmic earth ground (best possible if it all occurs at the exact same
earth ground point--or no current flows and there is no voltage
potential between such grounds.) For example, although a dipole needs
no rf ground directly at the point it connects to the feed-line, the rig
hooked to such an antenna and feed-line should be given a good earth ground.

If the above is coupled with a good understanding, awareness, and
practice of avoiding "ground loops", I think one can claim to have a
good and adequate grounding system. Ground loops are well discussed in
books, mags, and internet pages, etc.

In planes and outer space the earth ground can be ignored, your crafts
metallic shell will serve.

Regards,
JS

"John Smith" wrote in message
...
David wrote:
What would you define RF ground as? There seem to be a lot of different
ideas.

David:

Ground can be a relative thing. What I have always found to be good
advice is that EVERY ground, at some point, be allowed to reach a low
ohmic earth ground (best possible if it all occurs at the exact same earth
ground point--or no current flows and there is no voltage potential
between such grounds.) For example, although a dipole needs no rf ground
directly at the point it connects to the feed-line, the rig hooked to such
an antenna and feed-line should be given a good earth ground.
snip


Regards,
JS

When you refer to hooking the rig/dipole to a good earth ground, are you
still talking about an rf ground, or a safety ground?
I see no requirement to connect a nicely matched dipole to an earth ground
for rf purposes. For example, a battery operated transmitter feeding a
dummy load wouldn't need one either.

Wayne wrote:
"John Smith" wrote in message
...
David wrote:
What would you define RF ground as? There seem to be a lot of different
ideas.
David:

Ground can be a relative thing. What I have always found to be good
advice is that EVERY ground, at some point, be allowed to reach a low
ohmic earth ground (best possible if it all occurs at the exact same earth
ground point--or no current flows and there is no voltage potential
between such grounds.) For example, although a dipole needs no rf ground
directly at the point it connects to the feed-line, the rig hooked to such
an antenna and feed-line should be given a good earth ground.
snip

Regards,
JS

When you refer to hooking the rig/dipole to a good earth ground, are you
still talking about an rf ground, or a safety ground?
I see no requirement to connect a nicely matched dipole to an earth ground
for rf purposes. For example, a battery operated transmitter feeding a
dummy load wouldn't need one either.



Wayne:

Both. Only a dummy would think he needed an rf ground for a watt burner
of proper impedance.

However, there always is that "special case;" if the nitwit was running
a kw off a forklift battery, he just might want that rf ground.

JS

"John Smith" wrote in message
...
Wayne wrote:
"John Smith" wrote in message
...
David wrote:
What would you define RF ground as? There seem to be a lot of different
ideas.
David:

Ground can be a relative thing. What I have always found to be good
advice is that EVERY ground, at some point, be allowed to reach a low
ohmic earth ground (best possible if it all occurs at the exact same
earth ground point--or no current flows and there is no voltage
potential between such grounds.) For example, although a dipole needs
no rf ground directly at the point it connects to the feed-line, the rig
hooked to such an antenna and feed-line should be given a good earth
ground.
snip

Regards,
JS

When you refer to hooking the rig/dipole to a good earth ground, are you
still talking about an rf ground, or a safety ground?
I see no requirement to connect a nicely matched dipole to an earth
ground for rf purposes. For example, a battery operated transmitter
feeding a dummy load wouldn't need one either.

Wayne:

Both. Only a dummy would think he needed an rf ground for a watt burner
of proper impedance.

However, there always is that "special case;" if the nitwit was running a
kw off a forklift battery, he just might want that rf ground.

JS

Well, my question is in the context of rf ground being a function of the
antenna subsystem. It wasn't clear why you recommend use of a transmitter
rf ground, if the antenna system doesn't require it. Yes, I would run some
sort of rf ground at the rig if I were using a random wire fed with a tuner
in the shack, because the antenna system requires it.

My own setup is a ground mounted vertical with a modest 10 foot diameter
ground system. The "rf ground" is at the base of the antenna (as is a
separate lightning ground). The shack is on the second floor, and has only
a safety ground at the rig.

Wayne wrote:
"John Smith" wrote in message
...
Wayne wrote:
"John Smith" wrote in message
JS

Well, my question is in the context of rf ground being a function of the
antenna subsystem. It wasn't clear why you recommend use of a transmitter
rf ground, if the antenna system doesn't require it. Yes, I would run some
sort of rf ground at the rig if I were using a random wire fed with a tuner
in the shack, because the antenna system requires it.

My own setup is a ground mounted vertical with a modest 10 foot diameter
ground system. The "rf ground" is at the base of the antenna (as is a
separate lightning ground). The shack is on the second floor, and has only
a safety ground at the rig.


Wayne:

I see...

An antenna design requiring a system of underground ground radial(s) to
function correctly (or at least as designed), (or, for that matter,
above ground radial(s) running though bushes) would only be a "complete
antenna" if such were taken for granted had already been installed
(meaning the "rf ground-establishing" radials.)

And, if there were any chance at all I would be running a kw, and
touching both the ground radials and the ground at the same time AND
wanted to cover all special case/weird/worst-possible-cases (and I do
propose everyone should plan on this)... I would provide a nice low
ohmic earth ground for such radials (possibly useful for safety only.)
But then I am a sissy and find rf burns painful.

I didn't realize you were asking me, "If the guy has only installed half
of the antenna, should he install the "other half?" The answer to that
is all too obvious.

Yanno, those trick questions always throw me!

Regards,
JS