What is RF current?
 

Sorry for the dumb question, but I see the phrase "RF current" used in
so many contexts that I am not sure what it is.

What I "think" it is, is:

1. The sinusoidal, voltage / current that is impressed on the, e.g.,
coax feedline's center conductor by the transmitter (a.k.a.,
generator)

2. The voltage / current on the conductive portion of the radiator

3. The sinusoidal, voltage / current that is picked up by the "other"
conductive portion of the radiator (e.g., other pole of a dipole or
the ground, radials or counterpoise system of a vertical antenna)

4. The sinusoidal, voltage / current that is returned to the
transmitter via the shield of the coax.

5. The induced voltage / current in the counterpart of the receiving
system.

6. The current that "flows" in a dielectric, otherwise known as
displacement current, the original notion that allowed Maxwell to
posit the existence of the ether.

That is, RF current is no difference than "current" except for its
frequency.

What RF current is NOT is the transverse electromagnetic wave. That
is, once the effect is in the ether there is no RF current.

Looking for confirmation or refutation of the specific points above.

Thanks.

Thomas

Short response...

This pretty much describes what I think of when I hear the term. Current
at a "high" frequency. An object for discussion will certainly turn out to
be just when does the frequency get high enough to be considered RF and I
will say that I think that depends on a lot of things, the first probably
being wavelength, others being a matter of much discussion.





Verbose response...

Some pretty minor things...



RF Current, of course is the current, though you say "...voltage / current
...."



"sinusoidal"... If there are harmonics present, then there can be multiple
sine waves and the resultant (superposition of them) won't look sinusoidal,
but a sum of sines.



RE your #3:

I'd say that the current in a dipole (or ground plane, for that matter)
is "pushed into" one side and "pulled out of" the other side (the sides
alternating each half cycle) rather than being "picked up" by something
considered to be an "other side". If the coax center conductor happens to
be pushing at any given instant, then the shield is doing the accompanying
pulling. If we view the dipole with a balanced feed line, then the push &
pull may be easier to swallow. A dipole is balanced and there is a tendency
to consider the coax shield to be at ground potential at all times. This is
not correct and is at the root of a VERY large amount of discussion on these
news groups...



An RF "circuit", if you will, requires two connections to the source, just
like a bulb and battery. The rest of the "complete circuit" isn't as
obvious with RF -- as you appear to understand.



I also suspect you MAY get some discussion on displacement current since it
isn't being carried by the classical electrons-in-a-wire, but if the current
is present on both sides of the displacement current medium (say, a
capacitor dielectric), then there certainly must be RF current getting
through it somehow, so to speak.



RE the EM wave. I also think this is correct. You have the fields present
as though the voltages and currents were doing their thing, but there ain't
no electrons in space. This is a fascinating symbiotic (sp) relationship,
indeed...



73,
--
Steve N, K,9;d, c. i My email has no u's.

"Thomas" wrote in message
m...
Sorry for the dumb question, but I see the phrase "RF current" used in
so many contexts that I am not sure what it is.

What I "think" it is, is:

1. The sinusoidal, voltage / current that is impressed on the, e.g.,
coax feedline's center conductor by the transmitter (a.k.a.,
generator)

2. The voltage / current on the conductive portion of the radiator

3. The sinusoidal, voltage / current that is picked up by the "other"
conductive portion of the radiator (e.g., other pole of a dipole or
the ground, radials or counterpoise system of a vertical antenna)

4. The sinusoidal, voltage / current that is returned to the
transmitter via the shield of the coax.

5. The induced voltage / current in the counterpart of the receiving
system.

6. The current that "flows" in a dielectric, otherwise known as
displacement current, the original notion that allowed Maxwell to
posit the existence of the ether.

That is, RF current is no difference than "current" except for its
frequency.

What RF current is NOT is the transverse electromagnetic wave. That
is, once the effect is in the ether there is no RF current.

Looking for confirmation or refutation of the specific points above.

Thanks.

Thomas

On 16 Aug 2004 09:08:46 -0700, (Thomas) wrote:

Hi Thomas,

The statement that:
6. The current that "flows" in a dielectric, otherwise known as
displacement current,
contradicts:
What RF current is NOT is the transverse electromagnetic wave. That
is, once the effect is in the ether there is no RF current.

All alternating current seeks to escape out into the void of space.
Frequency merely tailors how effectively this is accomplished.
Current arises through the movement of charge (fairly built into a
physical process). This movement can be quite far away (even to the
point of the Butterfly effect) but still influence other physical
charges to mimic the movement. Hence there is the appearance of
continuity of the current even though there is no physical transport
capable of conducting that physical charge across that space.

In any current, if you could isolate and observe a specific, physical
charge; then you would observe that it travels no more than a meter a
second (if that fast). However, if you could isolate and observe two
specific, physical charges; then you could observe that when one
moved, the other would mimic that movement with nearly no delay and
the effect of that continuity is only limited by the speed of light
and the distance between those charges.

73's
Richard Clark, KB7QHC

Thomas wrote:

Sorry for the dumb question, but I see the phrase "RF current" used in
so many contexts that I am not sure what it is.

What I "think" it is, is:

1. The sinusoidal, voltage / current that is impressed on the, e.g.,
coax feedline's center conductor by the transmitter (a.k.a.,
generator)

No, current is not "voltage/current". It's current. Voltage is something
else. This comment applies to 2-5 also.

It also doesn't have to be sinusoidal.

2. The voltage / current on the conductive portion of the radiator

3. The sinusoidal, voltage / current that is picked up by the "other"
conductive portion of the radiator (e.g., other pole of a dipole or
the ground, radials or counterpoise system of a vertical antenna)

Now, the question is, how is that current "picked up"?


4. The sinusoidal, voltage / current that is returned to the
transmitter via the shield of the coax.

5. The induced voltage / current in the counterpart of the receiving
system.

6. The current that "flows" in a dielectric, otherwise known as
displacement current, the original notion that allowed Maxwell to
posit the existence of the ether.

That is, RF current is no difference than "current" except for its
frequency.

And the fact that it can "flow" through non-conductors as a
"displacement current". This can make its behavior a lot different than
zero-frequency current (DC).


What RF current is NOT is the transverse electromagnetic wave. That
is, once the effect is in the ether there is no RF current.

"Displacement current" IS an electromagnetic field. It's the mechanism
which induces conductive current in one conductor as a result of
conductive current in another. (This the answer to the question I asked
after point 3.)

Looking for confirmation or refutation of the specific points above.

Thanks.

Thomas

Roy Lewallen, W7EL