I have a question about AC Circuitry (as it relates to my antenna
system) where I cannot seem to arrive at an answer by reading reference
material:

The mechanics of current flow as it relates to a 1/4~ vertical
working against ground and separately, in comparison as it relates to
the dipole elements.

Is an AC circuit like DC, whereas there must be a ground return path
for a "flow" to happen ?

RE Dipole: If yes, then I get confused when thinking about ac current
flow relative to a dipole antenna. I can image current flow on the
center conductor side, since it seems the current +/- can keep going
back and forth from the transceiver to the end of the antenna element
(independent of the braid or other half side). But, it is hard to
understand how current can go back and forth on the braid side, since
it has a path to ground. Seems like on the braid side the current would
make its way down to the end of the dipole element and then start back,
but go right to the low impedance ground and be gone.

Vertical 1/4~: Again, here I image the ground side of the AC
circuit works as described above. But I read references to radials on
the ground side "collecting and returning ground currents" and that
confuses me. Returning currents to where ?, the current as pushed out
on the braid side seems to be where it was supposed to go - to ground.

Do both "legs" of AC current push out on the + and "pull" back on the -
, independent of 'ground' ?

I don't have an elec or engnr backgound so if you please to help me
understand, please try hard to keep it very basic. I just cannot use
math and AC formulas yet.

thanks, and 73, dennis

"k1drw" wrote in news:1167167054.718747.134870
@i12g2000cwa.googlegroups.com:

I have a question about AC Circuitry (as it relates to my antenna
system) where I cannot seem to arrive at an answer by reading reference
material:

The mechanics of current flow as it relates to a 1/4~ vertical
working against ground and separately, in comparison as it relates to
the dipole elements.

Is an AC circuit like DC, whereas there must be a ground return path
for a "flow" to happen ?

RE Dipole: If yes, then I get confused when thinking about ac current
flow relative to a dipole antenna. I can image current flow on the
center conductor side, since it seems the current +/- can keep going
back and forth from the transceiver to the end of the antenna element
(independent of the braid or other half side). But, it is hard to
understand how current can go back and forth on the braid side, since
it has a path to ground. Seems like on the braid side the current would
make its way down to the end of the dipole element and then start back,
but go right to the low impedance ground and be gone.

Vertical 1/4~: Again, here I image the ground side of the AC
circuit works as described above. But I read references to radials on
the ground side "collecting and returning ground currents" and that
confuses me. Returning currents to where ?, the current as pushed out
on the braid side seems to be where it was supposed to go - to ground.

Do both "legs" of AC current push out on the + and "pull" back on the -
, independent of 'ground' ?

I don't have an elec or engnr backgound so if you please to help me
understand, please try hard to keep it very basic. I just cannot use
math and AC formulas yet.

You can sometimes model an antenna as a set of lumped circuit constants,
but, in actual fact, at least one of these must represent the induced
impedance of the space around it. After all, that's what the antenna
really is--a device to couple energy from the feedline into the space
surrounding the antenna, where it will be lost to radiation.

I realize this isn't going to be that satisfactory an answer. Ground
currents do flow in radials and, because they (theoretically) flow equally
in opposite directions should add up to close to ZERO at the coax braid.

The current at the base of the antenna is high (the only thing keeping it
from trying to be a short circuit is the radiation resistance and any
resistive losses in the antenna itself). But it need not be matched by any
currents elsewhere. It IS "matched" by the induced radiation in free
space, though.

--
Dave Oldridge+
ICQ 1800667

You are correct Dave, I did not get much out of your response. Again,
my knowledge and experience level is such that I have no idea what a
lumped circuit constant is.

What is the current flow as it leaves the transceiver, down each of the
two pieces of the coax, in very fundamental terms ? Is there a picture
or an animation you can point me to so that I may visualize what is
actually happening (assuming no impedance mismatch).

I am having difficulty visualizing the current flow in the circuit.
Going beyond that with a description of other activity and components
and variables, is not what I am hoping to understand initially. When
you say "current at the base of the antenna is high", that still does
not help me visualize what is actually, fundamentally happening.
Current is flowing, ok, I assume up and down the coax on both
conductors (+ and -) and into the antenna elements. Referring back to
my original post, for the 1/4~ vertical, current is flowing into the
vertical radiator via the coax center conductor and into the ground
radials from the inside face of the coax shield. I seem to think that
current is also flowing into the radials from other sources, but input
from the tail end of the radials. Now what.? Does the current flow go
back to the source (the transceiver) and then turn around and combine
with more current coming out of the transceiver ? What for ? Why is
current flowing into the radials from the transceiver - what purpose ?
I can see the purpose of current flowing into the upright vertical
element and being radiated. I don't understand the PURPOSE and
disposition of current flowing into the radials from either source.

I really want to understand this fundamental concept but seem to have
difficulty explaining myself because the responses are not anywhere
near what I need explained in a very basic way.

If you would please take another shot at explaining what you think I am
asking, it would be appreciated.

Same thing for Cecil. Just a very, very clear, basic explanation of
the current flow in both pieces of the coax, into the antenna elements
(on the vertical, the antenna 'elements' are the vertical radiator and
the ground radials).

sincere thanks for any repsonse.

73, dennis

k1drw wrote:
Same thing for Cecil. Just a very, very clear, basic explanation of
the current flow in both pieces of the coax, into the antenna elements
(on the vertical, the antenna 'elements' are the vertical radiator and
the ground radials).

Let's say we have two wires running out to a load.
If we hook a 12 volt battery to those two wires,
DC current flows out to the load through one of
the wires and back to the battery through the
other wire such that the current loop is closed.

With an AC signal, current flows out through one
wire and back through the other for 1/2 cycle.
It then reverses direction in both wires for
the other 1/2 cycle.

Coax is like those two wires. The center conductor
of the coax is one wire and the inside of the
coax braid is the other conductor. When current
is flowing out through the center conductor, it
is flowing back through the braid. 1/2 cycle later
both currents are reversed.

When current is flowing into the vertical antenna
element, an equal amount of current is flowing
out of the radials. 1/2 cycle later, current is
flowing out of the vertical antenna element and
into the radials. Radiation losses from the
antenna and radials make it look like there
might be a 35 ohm resistor attached to the
end of the coax instead of the antenna.
--
73, Cecil http://www.w5dxp.com

Hello Cecil:

Once again, I extend thanks to you for your 'elmering'. I
understood your response completely.

the vertical configuration: It seems then, that the 2nd half
of the cycle on the vertical (where the current flow is coming out of
the vertical element and into the radials) is practically worthless in
terms of radiating signal into the 'ether'. At first thought it would
appear that there is more efficiency with an elevated 1/4~ vertical
element and using elevated radials and or counterpoise -vs- ground
radials.

Cecil, I can only offer thanks, but it is many thanks...!

73, dennis, k1drw

k1drw wrote:
the vertical configuration: It seems then, that the 2nd half
of the cycle on the vertical (where the current flow is coming out of
the vertical element and into the radials) is practically worthless in
terms of radiating signal into the 'ether'.

Dennis, you got the simplified version. When current is
flowing into the antenna, electrons are flowing out of
the antenna. When current is flowing out of the antenna,
electrons are flowing into the antenna. Either way the
electrons are flowing, they are being accelerated for
part of the cycle. So RF radiation (photon generation)
occurs no matter which way the electrons are flowing.

In addition, the vertical is a standing wave antenna.
It actually has RF waves moving both directions at the
same time. There's the forward wave moving toward the
top of the antenna and the reflected wave moving from
the top back toward the feedpoint. The SWR on a 1/2
wavelength dipole is in the ballpark of 20:1.

For an antenna to be close to 100% efficient, it must
radiate equally during both half cycles.

You can blame Ben Franklin for current flowing the opposite
direction from the electron flow. He didn't know electrons
carried a negative charge. So by definition, current flows
from plus to minus but electrons actually flow from minus
to plus. In addition, RF current flow is associated with
the RF electromagnetic wave (photons) , not with the
electrons which move much slower than the speed of light.
--
73, Cecil http://www.w5dxp.com

k1drw wrote:
Seems like on the braid side the current would
make its way down to the end of the dipole element and then start back,
but go right to the low impedance ground and be gone.

Except it is not DC. If that coax is an odd multiple
of 1/4 wavelengths long, the impedance looking down
the outside of the braid is very, very high. Or if
a choke is installed on the coax, the impedance may
be very high. On a macro scale, RF obeys the rules
of the distributed network model and doesn't respond
like DC.
--
73, Cecil http://www.w5dxp.com

k1drw wrote:
I have a question about AC Circuitry (as it relates to my antenna
system) where I cannot seem to arrive at an answer by reading reference
material:

The mechanics of current flow as it relates to a 1/4~ vertical
working against ground and separately, in comparison as it relates to
the dipole elements.

Is an AC circuit like DC, whereas there must be a ground return path
for a "flow" to happen ?

Yes.

RE Dipole: If yes, then I get confused when thinking about ac current
flow relative to a dipole antenna. I can image current flow on the
center conductor side, since it seems the current +/- can keep going
back and forth from the transceiver to the end of the antenna element
(independent of the braid or other half side). But, it is hard to
understand how current can go back and forth on the braid side, since
it has a path to ground. Seems like on the braid side the current would
make its way down to the end of the dipole element and then start back,
but go right to the low impedance ground and be gone.

Current flows into one half the antenna, which causes it to create a
field. The field strikes the other half of the dipole, inducing a
current in it. The current into one half the dipole has to equal, at
every instant, the current out of the other half. The path is through
the air, with the coupling mechanism being the electric and magnetic
fields. If this is hard to swallow, think a bit about how current flows
"through" a capacitor or transformer.

Vertical 1/4~: Again, here I image the ground side of the AC
circuit works as described above. But I read references to radials on
the ground side "collecting and returning ground currents" and that
confuses me. Returning currents to where ?, the current as pushed out
on the braid side seems to be where it was supposed to go - to ground.

The field created by the current in the vertical couples to the ground,
and induces a current in it. This current flows in the braid. The
current into the vertical has to, at every instant, equal the current
flowing out of the ground. The radials lower the resistance of the
current path through the ground.

Do both "legs" of AC current push out on the + and "pull" back on the -
, independent of 'ground' ?

Sorry, I don't know what a current "leg" is.

I don't have an elec or engnr backgound so if you please to help me
understand, please try hard to keep it very basic. I just cannot use
math and AC formulas yet.

Hope this helps. A quantitative understanding requires an extensive math
background.

Roy Lewallen, W7EL

Roy:
Very well explained. Thank you kindly...!

Your explanation and Cecil's were very clear and easy to
understand. Sincere thanks for taking time. I very much appreciate
the elmering.

respectfully,
Dennis R. Wells Sr., k1drw