I am in the process of trying to gain a better understanding of amateur
radio antennas and transmission line issues.

I am mulling-over the issues associated with driving a dipole. Let's
say I have a (resonant) dipole close to ground, but perfectly
symmetrical. If I were to drive the dipole from a grounded radio
transmitter through some length of coaxial cable, I would expect that
the drive voltages at the driving point of each wire (measured with
respect to ground) would be far from equal and opposite. As a result,
I would expect that some current would need to return to the ground
terminal at the transmitter through some means other than the inner
surface of the coax shield. This spurious current could return on the
outside of the shield and/or through the ground itself, leading to line
radfiation and/or power loss. Of course, I would not expect a ladder
line to solve the basic problem.

So, it would seem that driving a dipole directly with coax is not the
best way to do things. Is that correct?

I suppose one needs a so-called "current balun" to ensure that the
antenna currents are equal and opposite, avoiding a spurious return
current. My simplistic way of understanding why all of the return
current flows along the inside of the braid is that the outside of the
braid is shielded from the center conductor, resulting in a huge
outer-braid loop inductance. And current takes the path of least
impedance, which is the low-inductance loop formed by the center
conductor and inner-braid.

That's it for now. Any comments will be appreciated.

73
-JJ

If you can find the publications, I recommend that you read "Some
Aspects of the Balun Problem" by Walt Maxwell, W2DU, in March 1983 QST,
and "Baluns: What They Do and How They Do It" in the ARRL Antenna
Compendium, Vol. 1.

Roy Lewallen, W7EL

wrote:
I am in the process of trying to gain a better understanding of amateur
radio antennas and transmission line issues.

I am mulling-over the issues associated with driving a dipole. Let's
say I have a (resonant) dipole close to ground, but perfectly
symmetrical. If I were to drive the dipole from a grounded radio
transmitter through some length of coaxial cable, I would expect that
the drive voltages at the driving point of each wire (measured with
respect to ground) would be far from equal and opposite. As a result,
I would expect that some current would need to return to the ground
terminal at the transmitter through some means other than the inner
surface of the coax shield. This spurious current could return on the
outside of the shield and/or through the ground itself, leading to line
radfiation and/or power loss. Of course, I would not expect a ladder
line to solve the basic problem.

So, it would seem that driving a dipole directly with coax is not the
best way to do things. Is that correct?

I suppose one needs a so-called "current balun" to ensure that the
antenna currents are equal and opposite, avoiding a spurious return
current. My simplistic way of understanding why all of the return
current flows along the inside of the braid is that the outside of the
braid is shielded from the center conductor, resulting in a huge
outer-braid loop inductance. And current takes the path of least
impedance, which is the low-inductance loop formed by the center
conductor and inner-braid.

That's it for now. Any comments will be appreciated.

73
-JJ

Roy

Do you have any suggestions for my locating Walter Maxwell's publication
on baluns? Also, where can I buy the ARRL Antenna Compendium Vol. 1?
I'll go to Google right now to try to locate the ARRL publication on
antennas.

Jerry



"Roy Lewallen" wrote in message
...
If you can find the publications, I recommend that you read "Some Aspects
of the Balun Problem" by Walt Maxwell, W2DU, in March 1983 QST, and
"Baluns: What They Do and How They Do It" in the ARRL Antenna Compendium,
Vol. 1.

Roy Lewallen, W7EL

wrote:
I am in the process of trying to gain a better understanding of amateur
radio antennas and transmission line issues.

I am mulling-over the issues associated with driving a dipole. Let's
say I have a (resonant) dipole close to ground, but perfectly
symmetrical. If I were to drive the dipole from a grounded radio
transmitter through some length of coaxial cable, I would expect that
the drive voltages at the driving point of each wire (measured with
respect to ground) would be far from equal and opposite. As a result,
I would expect that some current would need to return to the ground
terminal at the transmitter through some means other than the inner
surface of the coax shield. This spurious current could return on the
outside of the shield and/or through the ground itself, leading to line
radfiation and/or power loss. Of course, I would not expect a ladder
line to solve the basic problem.

So, it would seem that driving a dipole directly with coax is not the
best way to do things. Is that correct?

I suppose one needs a so-called "current balun" to ensure that the
antenna currents are equal and opposite, avoiding a spurious return
current. My simplistic way of understanding why all of the return
current flows along the inside of the braid is that the outside of the
braid is shielded from the center conductor, resulting in a huge
outer-braid loop inductance. And current takes the path of least
impedance, which is the low-inductance loop formed by the center
conductor and inner-braid.

That's it for now. Any comments will be appreciated.

73
-JJ

On Tue, 22 Feb 2005 01:30:35 GMT, "Jerry Martes"
wrote:

Roy

Do you have any suggestions for my locating Walter Maxwell's publication
on baluns? Also, where can I buy the ARRL Antenna Compendium Vol. 1?
I'll go to Google right now to try to locate the ARRL publication on
antennas.

Jerry

Maxwell's home page is at http://home.iag.net/~w2du/ where you'll find
his article on baluns.

For the Antenna Compendium(s), go to www.arrl.org and then to their
bookstore where all of their antenna books are for sale.

bob
k5qwg




"Roy Lewallen" wrote in message
...
If you can find the publications, I recommend that you read "Some Aspects
of the Balun Problem" by Walt Maxwell, W2DU, in March 1983 QST, and
"Baluns: What They Do and How They Do It" in the ARRL Antenna Compendium,
Vol. 1.

Roy Lewallen, W7EL

wrote:
I am in the process of trying to gain a better understanding of amateur
radio antennas and transmission line issues.

I am mulling-over the issues associated with driving a dipole. Let's
say I have a (resonant) dipole close to ground, but perfectly
symmetrical. If I were to drive the dipole from a grounded radio
transmitter through some length of coaxial cable, I would expect that
the drive voltages at the driving point of each wire (measured with
respect to ground) would be far from equal and opposite. As a result,
I would expect that some current would need to return to the ground
terminal at the transmitter through some means other than the inner
surface of the coax shield. This spurious current could return on the
outside of the shield and/or through the ground itself, leading to line
radfiation and/or power loss. Of course, I would not expect a ladder
line to solve the basic problem.

So, it would seem that driving a dipole directly with coax is not the
best way to do things. Is that correct?

I suppose one needs a so-called "current balun" to ensure that the
antenna currents are equal and opposite, avoiding a spurious return
current. My simplistic way of understanding why all of the return
current flows along the inside of the braid is that the outside of the
braid is shielded from the center conductor, resulting in a huge
outer-braid loop inductance. And current takes the path of least
impedance, which is the low-inductance loop formed by the center
conductor and inner-braid.

That's it for now. Any comments will be appreciated.

73
-JJ

On Mon, 21 Feb 2005 17:25:06 -0800, Roy Lewallen
wrote:

If you can find the publications, I recommend that you read "Some
Aspects of the Balun Problem" by Walt Maxwell, W2DU, in March 1983 QST,
and "Baluns: What They Do and How They Do It" in the ARRL Antenna
Compendium, Vol. 1.

Excellent advise!

You can find Walter's article he
http://home.iag.net/~w2du/Reflection...nProblem. pdf

Danny, K6MHE

Thanks Bob I printed the balun article. I see a whole lot of other stuff
at that site. Walter Maxwell has to be as good as it gets for any info on
things that interest me. You did me a favor by leading me to that info.

Thanks again
Jerry


"Bob Miller" wrote in message
...
On Tue, 22 Feb 2005 01:30:35 GMT, "Jerry Martes"
wrote:

Roy

Do you have any suggestions for my locating Walter Maxwell's publication
on baluns? Also, where can I buy the ARRL Antenna Compendium Vol. 1?
I'll go to Google right now to try to locate the ARRL publication on
antennas.

Jerry

Maxwell's home page is at http://home.iag.net/~w2du/ where you'll find
his article on baluns.

For the Antenna Compendium(s), go to www.arrl.org and then to their
bookstore where all of their antenna books are for sale.

bob
k5qwg




"Roy Lewallen" wrote in message
...
If you can find the publications, I recommend that you read "Some
Aspects
of the Balun Problem" by Walt Maxwell, W2DU, in March 1983 QST, and
"Baluns: What They Do and How They Do It" in the ARRL Antenna
Compendium,
Vol. 1.

Roy Lewallen, W7EL

wrote:
I am in the process of trying to gain a better understanding of amateur
radio antennas and transmission line issues.

I am mulling-over the issues associated with driving a dipole. Let's
say I have a (resonant) dipole close to ground, but perfectly
symmetrical. If I were to drive the dipole from a grounded radio
transmitter through some length of coaxial cable, I would expect that
the drive voltages at the driving point of each wire (measured with
respect to ground) would be far from equal and opposite. As a result,
I would expect that some current would need to return to the ground
terminal at the transmitter through some means other than the inner
surface of the coax shield. This spurious current could return on the
outside of the shield and/or through the ground itself, leading to line
radfiation and/or power loss. Of course, I would not expect a ladder
line to solve the basic problem.

So, it would seem that driving a dipole directly with coax is not the
best way to do things. Is that correct?

I suppose one needs a so-called "current balun" to ensure that the
antenna currents are equal and opposite, avoiding a spurious return
current. My simplistic way of understanding why all of the return
current flows along the inside of the braid is that the outside of the
braid is shielded from the center conductor, resulting in a huge
outer-braid loop inductance. And current takes the path of least
impedance, which is the low-inductance loop formed by the center
conductor and inner-braid.

That's it for now. Any comments will be appreciated.

73
-JJ

You can have a look here for antenna plans and antenna theory

http://www.dxzone.com/