Alternatives...
 

Bottom posted...

"Cecil Moore" wrote in message
. com...
chuck wrote:
So here is my main question: do we object to the vertical radiation per
se ...?

Maybe an example would help. I model a dipole until
I am happy with the results predicted by EZNEC. The
take-off-angle is perfect for my schedule to AZ.
EZNEC assumes no feedline radiation. I am sloppy
about putting my dipole in the air and lots of feedline
radiation results which goes off in directions not
predicted by EZNEC. Murphey's Law predicts that the
unknown directions will be bad (entropy never
decreases). Besides, half of my feedline is routed
horizontal under the eaves of my house.

So would you rather deal with the devil you know or
trust the angel that you don't know? Does the angel
that you are trusting really understand entropy?
--
73, Cecil http://www.qsl.net/w5dxp

That's a fair question; but here are a few mo

If you have X amount of time available to fuss around trying to
minimize feedline radiation, might you rather spend that time:
1. Having more or longer QSOs with your AZ friend?
2. Working a little DX?
3. Improving your audio?
4. Watching a movie?
5. Making whoopie with the XYL?
6. Any number of other possibilities?

Disclaimer: Nothing should be inferred from the (more-or-less
random) order of the above list. ;-)

73, Ed

Alternatives...
 

Old Ed wrote:
That's a fair question; but here are a few mo

If you have X amount of time available to fuss around trying to
minimize feedline radiation, might you rather spend that time:

If one follows good engineering practice, it becomes second
nature after awhile and consumes only a negligible amount
of time which is usually more than worth it. If it takes
someone more time to learn about feedline radiation than
they are willing to spend, well then what-the-hell,
ignorance is bliss.

1. Having more or longer QSOs with your AZ friend?

We run out of things to talk about as it is.

2. Working a little DX?

Most of them don't speak Texan.

3. Improving your audio?

I'm already famous for my audio. I do a mean Johnny Cash.
I'm also not bad at Elvis. I'm lead bass in the church
choir. They call me the "largemouth bass".

4. Watching a movie?

The last movies that I really enjoyed were "Patton" and
"Alien". Most movies put me to sleep (which is not a bad
thing). If you enjoy homosexual sheephearders - well,
it takes all kinds.

5. Making whoopie with the XYL?

Divorced in 1984 - I wish it had been sooner.

6. Any number of other possibilities?

I do have a part time teaching job and I like riding
my Harley. I also just spent about three hours getting
my birdhouse ready for the Purple Martins that are
returning from Brazil to nest in East Texas. The fact
that I am posting to this newsgroup at this time means
that I don't have anything interesting or productive
to do. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Q about balanced feed line
 

chuck wrote:
. . .
So here is my main question: do we object to the vertical radiation per
se (i.e., if we wanted vertically polarized radiation, we would have put
up a vertical in the first place), or is radiation from an unbalanced
line somehow more insidious in that it causes other problems that
"ordinary" verticals do not cause? In other words, why do we really care
about imbalance?
. . .

Would you intentionally load up your house wiring an use it as an antenna?

Roy Lewallen, W7EL

Q about balanced feed line
 

Of course not, Roy. I sure hope what I wrote did not suggest otherwise.
But I am trying to learn exactly which properties of an antenna system
cause house wiring to be "loaded up."

In particular, I am trying to establish whether a top-loaded vertical
with the same wire geometry and RF ground as the open-wire transmission
line-fed dipole would be just as likely to cause undesirable coupling to
the house wiring. It seems to me that it is. If it is not, I'm trying to
understand why not.

In other words, is the problem transmission line unbalance, or simply
having a radiator with undesirable proximity to house wiring?

One more way to word the question: if you tie the open-wire lines
together at the tuner/transmitter and feed the antenna as a vertical,
all of the current in the line will be common-mode. Would that be less
likely to cause undesirable coupling than the exact same antenna with
transmission line unbalance.

I am not advocating unbalanced transmission lines, verticals, or the
pursuit of radiation patterns one knows in advance to be undesirable.

I apologize for my prolix and obtuse approach, but I'm not sure how to
pose the question properly. I'll try to work on that.

Thanks again.

Chuck

Roy Lewallen wrote:
chuck wrote:

. . .
So here is my main question: do we object to the vertical radiation
per se (i.e., if we wanted vertically polarized radiation, we would
have put up a vertical in the first place), or is radiation from an
unbalanced line somehow more insidious in that it causes other
problems that "ordinary" verticals do not cause? In other words, why
do we really care about imbalance?

. . .

Would you intentionally load up your house wiring an use it as an antenna?

Roy Lewallen, W7EL

Q about balanced feed line
 

As a follow-up, is there a practical way to determine how much current
unbalance will cause a one dB reduction in power delivered to the
antenna, the "lost power" being that power radiated by the transmission
line?

It seems like a rather complex modeling problem.

Thanks!

Chuck, NT3G







ig Endian wrote:
How does one check the balance between two parallel feed wires into a
doublet antenna. Neon bulbs or some sort of meter gizmo?

tnx

d

Q about balanced feed line
 

On Mon, 27 Feb 2006 14:29:47 GMT, chuck wrote:

One more way to word the question: if you tie the open-wire lines
together at the tuner/transmitter and feed the antenna as a vertical,
all of the current in the line will be common-mode. Would that be less
likely to cause undesirable coupling than the exact same antenna with
transmission line unbalance.

Hi Chuck,

When you tie them together, you have to be referencing that "common"
lead to something. Usually that something is ground. Common Mode
current springs into existence by definition.

Where did ground come into the picture? Usually through the power
supply. The power supply gets it from the mains, and thus you see the
origin of getting RF into the house.

I wrote earlier about how a religious devotion to balancing an
antenna/feed can be easily disturbed when you connect your line to the
rig. The rig has a ground connection even if you didn't drive a
ground rod specifically for it, nor purposely establish a ground path.

Some might think that their tuner isolates their twin line feed from
ground. I seriously doubt that is true. Most tuners I've seen use a
voltage BalUn which design violates that form of isolation, or turns
the core into a heating element, or both. Even link tuners have the
prospects of not having a truly balanced connection. I would say the
prospects are much better, as the designers were working toward that
goal, but it is not always achieved.

73's
Richard Clark, KB7QHC

Q about balanced feed line
 

chuck wrote:
Of course not, Roy. I sure hope what I wrote did not suggest
otherwise. But I am trying to learn exactly which properties of an
antenna system cause house wiring to be "loaded up."

In particular, I am trying to establish whether a top-loaded vertical
with the same wire geometry and RF ground as the open-wire
transmission line-fed dipole would be just as likely to cause
undesirable coupling to the house wiring. It seems to me that it is.
If it is not, I'm trying to understand why not.

When you have common mode current, it not only flows on the feedline,
but continues to ground via whatever path it can. And this is usually
the house wiring. So your antenna now consists of the "antenna", the
feedline, and the house wiring. The problem here is current in house
wiring due to conduction, not coupling.

If you properly feed a vertical, no RF current is conducted to the house
wiring. Either a properly fed vertical or a radiating feedline can
induce current in the house wiring by coupling, but the amount will
depend on (among other things) proximity of the antenna or feedline to
the house. Most of us can put a vertical at least a little distance from
the house, but the feedline has to come right in.

In other words, is the problem transmission line unbalance, or simply
having a radiator with undesirable proximity to house wiring?

Again, the problems are twofold. One is conducted current, and the other
is coupled current due to proximity.

One more way to word the question: if you tie the open-wire lines
together at the tuner/transmitter and feed the antenna as a vertical,
all of the current in the line will be common-mode. Would that be
less likely to cause undesirable coupling than the exact same antenna
with transmission line unbalance.

You would have exactly the same problems in either case, assuming a
worst case of imbalance when feeding the antenna normally (which isn't
likely). Whatever current leaves the rig via the connected-together
feedline conductors (or via common mode current in a normally fed
antenna), an equal amount of current has to leave the rig via its
chassis or "ground" connection. In a properly fed vertical, this current
ends up in the ground system at the base of the antenna. In the
tied-together feed, it'll end up getting to ground however it can,
radiating and inducing other currents along the way.

. . .

Roy Lewallen, W7EL

Q about balanced feed line
 

chuck wrote:
As a follow-up, is there a practical way to determine how much current
unbalance will cause a one dB reduction in power delivered to the
antenna, the "lost power" being that power radiated by the transmission
line?

It seems like a rather complex modeling problem.

Thanks!

Chuck, NT3G

Nope. You can't generally say that one part of an antenna is radiating a
particular amount of the total power. Each part of the antenna creates a
field, and it interacts with the fields from all other parts of the
antenna. The total power radiated has to equal the total power input
less loss, but that's all you can say for sure. An example will help
illustrate the problem. Consider a parasitic element in a Yagi. It has
considerable current and contributes a great deal to the overall
pattern. Yet the total power input to the Yagi element is zero. With
zero power input, it can't, by itself, be radiating any power. What it
does is intercept some of the power radiated by the driven element and
re-radiates it with a different phase and amplitude. So how would you
apportion the power radiated by the driven element and the parasitic
element?

You might take a look at the current in the driven element and note that
it increases or decreases as you put the parasitic element in place and
remove it. But the current can either increase or decrease, depending on
the length and spacing of the parasitic element. So has the parasitic
element increased or decreased the power radiated by the driven element?
There's no answer.

You can look at the change in pattern in some idealized cases by
modeling. This can tell you what range of effects you might expect in a
real situation.

Roy Lewallen, W7EL

Q about balanced feed line
 

In article ,
Roy Lewallen wrote:

chuck wrote:
Of course not, Roy. I sure hope what I wrote did not suggest
otherwise. But I am trying to learn exactly which properties of an
antenna system cause house wiring to be "loaded up."

In particular, I am trying to establish whether a top-loaded vertical
with the same wire geometry and RF ground as the open-wire
transmission line-fed dipole would be just as likely to cause
undesirable coupling to the house wiring. It seems to me that it is.
If it is not, I'm trying to understand why not.

When you have common mode current, it not only flows on the feedline,
but continues to ground via whatever path it can. And this is usually
the house wiring. So your antenna now consists of the "antenna", the
feedline, and the house wiring. The problem here is current in house
wiring due to conduction, not coupling.

If you properly feed a vertical, no RF current is conducted to the house
wiring. Either a properly fed vertical or a radiating feedline can
induce current in the house wiring by coupling, but the amount will
depend on (among other things) proximity of the antenna or feedline to
the house. Most of us can put a vertical at least a little distance from
the house, but the feedline has to come right in.

In other words, is the problem transmission line unbalance, or simply
having a radiator with undesirable proximity to house wiring?

Again, the problems are twofold. One is conducted current, and the other
is coupled current due to proximity.

One more way to word the question: if you tie the open-wire lines
together at the tuner/transmitter and feed the antenna as a vertical,
all of the current in the line will be common-mode. Would that be
less likely to cause undesirable coupling than the exact same antenna
with transmission line unbalance.

You would have exactly the same problems in either case, assuming a
worst case of imbalance when feeding the antenna normally (which isn't
likely). Whatever current leaves the rig via the connected-together
feedline conductors (or via common mode current in a normally fed
antenna), an equal amount of current has to leave the rig via its
chassis or "ground" connection. In a properly fed vertical, this current
ends up in the ground system at the base of the antenna. In the
tied-together feed, it'll end up getting to ground however it can,
radiating and inducing other currents along the way.

. . .

Roy Lewallen, W7EL

Here is something strange I discovered this weekend. While using a F.S.
meter as a RF sniffer, I was probing along some lamp cords that are
plugged into one of those extention outlet strips. I have a split block
ferrite core which measures one inch square and a 1/2 inch ID hole. So
while monitoring the FS meter I placed the core on the 115 to the house
outlet thinking that I will see a decrease in FS reading, much to my
surprise just the opposite happened, the FS meter pegged out. Why would
adding the core cause the FS reading to increase?

Q about balanced feed line
 

Big Endian wrote:

Here is something strange I discovered this weekend. While using a F.S.
meter as a RF sniffer, I was probing along some lamp cords that are
plugged into one of those extention outlet strips. I have a split block
ferrite core which measures one inch square and a 1/2 inch ID hole. So
while monitoring the FS meter I placed the core on the 115 to the house
outlet thinking that I will see a decrease in FS reading, much to my
surprise just the opposite happened, the FS meter pegged out. Why would
adding the core cause the FS reading to increase?

There are at least three possible explanations.

The first is one I've come across many times in doing EMI work, and is
probably the most likely. What happens is that you've got two or more
radiating sources whose fields cancel or partially cancel at the field
strength meter. When you reduce the radiation from one of those sources,
the field at the meter increases.

The second can be a bit subtle. Suppose you have a wire near an antenna
and that wire is, say, 3/4 wavelength long. Very little current will be
induced in this wire because it's far from self-resonance. Now put a
choke in the wire 1/4 wavelength from one end. Presto, a lot of induced
current in the now-isolated 1/2 wavelength portion. This phenomenon can
cause common mode current to increase when you add a common mode choke
on the feedline, if the current is being induced in the feedline (as
opposed to conducted) and the wire length and choke position are
favorable for this to happen.

The third is that the core you're using is a high frequency ferrite. If
it is, it will act as a loading coil, which could make a previously
non-resonant system resonant. I don't think this is likely, though,
because most clamp-on cores are made from ferrites suitable for EMI
suppression. A common type of material for this purpose is type 43
ferrite, which has a Q of 1 at a few MHz. So this type of ferrite won't
cause resonant effects like a high frequency ferrite (e.g., type 61) would.

Roy Lewallen, W7EL

Q about balanced feed line
 

In article ,
Roy Lewallen wrote:

Big Endian wrote:

Here is something strange I discovered this weekend. While using a F.S.
meter as a RF sniffer, I was probing along some lamp cords that are
plugged into one of those extention outlet strips. I have a split block
ferrite core which measures one inch square and a 1/2 inch ID hole. So
while monitoring the FS meter I placed the core on the 115 to the house
outlet thinking that I will see a decrease in FS reading, much to my
surprise just the opposite happened, the FS meter pegged out. Why would
adding the core cause the FS reading to increase?

There are at least three possible explanations.

The first is one I've come across many times in doing EMI work, and is
probably the most likely. What happens is that you've got two or more
radiating sources whose fields cancel or partially cancel at the field
strength meter. When you reduce the radiation from one of those sources,
the field at the meter increases.

The second can be a bit subtle. Suppose you have a wire near an antenna
and that wire is, say, 3/4 wavelength long. Very little current will be
induced in this wire because it's far from self-resonance. Now put a
choke in the wire 1/4 wavelength from one end. Presto, a lot of induced
current in the now-isolated 1/2 wavelength portion. This phenomenon can
cause common mode current to increase when you add a common mode choke
on the feedline, if the current is being induced in the feedline (as
opposed to conducted) and the wire length and choke position are
favorable for this to happen.

The third is that the core you're using is a high frequency ferrite. If
it is, it will act as a loading coil, which could make a previously
non-resonant system resonant. I don't think this is likely, though,
because most clamp-on cores are made from ferrites suitable for EMI
suppression. A common type of material for this purpose is type 43
ferrite, which has a Q of 1 at a few MHz. So this type of ferrite won't
cause resonant effects like a high frequency ferrite (e.g., type 61) would.

Roy Lewallen, W7EL

I suppose the right thing to do is to place ferrite cores on all the
conductors in the area. Could get expensive. I have so many wires all
over the place the job seems a bit hopeless.

Thanks for the information Roy.

Q about balanced feed line
 

Big Endian wrote:

I suppose the right thing to do is to place ferrite cores on all the
conductors in the area. Could get expensive. I have so many wires all
over the place the job seems a bit hopeless.
. . .

Well, that's one way to solve the problem. Like the sign over my desk
says, "Anyone can design a bridge that will stand up. It takes an
engineer to design a bridge that will barely stand up."

Roy Lewallen, W7EL

Q about balanced feed line
 

Big Endian wrote:
In article ,
Roy Lewallen wrote:

Big Endian wrote:

Here is something strange I discovered this weekend. While using a F.S.
meter as a RF sniffer, I was probing along some lamp cords that are
plugged into one of those extention outlet strips. I have a split block
ferrite core which measures one inch square and a 1/2 inch ID hole. So
while monitoring the FS meter I placed the core on the 115 to the house
outlet thinking that I will see a decrease in FS reading, much to my
surprise just the opposite happened, the FS meter pegged out. Why would
adding the core cause the FS reading to increase?

There are at least three possible explanations.

The first is one I've come across many times in doing EMI work, and is
probably the most likely. What happens is that you've got two or more
radiating sources whose fields cancel or partially cancel at the field
strength meter. When you reduce the radiation from one of those sources,
the field at the meter increases.

The second can be a bit subtle. Suppose you have a wire near an antenna
and that wire is, say, 3/4 wavelength long. Very little current will be
induced in this wire because it's far from self-resonance. Now put a
choke in the wire 1/4 wavelength from one end. Presto, a lot of induced
current in the now-isolated 1/2 wavelength portion. This phenomenon can
cause common mode current to increase when you add a common mode choke
on the feedline, if the current is being induced in the feedline (as
opposed to conducted) and the wire length and choke position are
favorable for this to happen.

The third is that the core you're using is a high frequency ferrite. If
it is, it will act as a loading coil, which could make a previously
non-resonant system resonant. I don't think this is likely, though,
because most clamp-on cores are made from ferrites suitable for EMI
suppression. A common type of material for this purpose is type 43
ferrite, which has a Q of 1 at a few MHz. So this type of ferrite won't
cause resonant effects like a high frequency ferrite (e.g., type 61) would.

Roy Lewallen, W7EL

I suppose the right thing to do is to place ferrite cores on all the
conductors in the area. Could get expensive. I have so many wires all
over the place the job seems a bit hopeless.

Thanks for the information Roy.

Another option is to place a choke in the mains supply for the entire
station. If the RF current path is down the feedline (in common mode)
and then out into the mains, you can reduce it by inserting a choke at
any point along its path, and the mains supply may be more convenient
place.

The mains supply would need a different kind of RF choke, of course. One
option is to wind the entire mains cable - one or both live conductors,
neutral and safety ground - on a stack of large toroids (bearing in mind
what Roy said above, about choosing the right material). Another option
is to buy a ready-made mains filter that also has an RF choke in the
ground lead.

The difficulty is to organize the mains wiring so that *everything*
passes through the choke. If you leave even one sneak path to ground,
the RF will happily use it! Also any other lines such as phone and
network connections need RF chokes of their own. If this starts to read
like the things you have to do for lightning protection... why, that's
perfectly true because very similar considerations apply.

Groveling on your knees under the table is a chore, and of course it's
totally beneath the dignity of a Licensed Radio Armature. Well, do it
anyway. At my old QTH I found it well worth the effort. Re-grouping all
the mains feeds through a single filter cleaned up my mains-borne TVI,
and it also reduced the computer and other noise that was coming *up*
the mains.

Another very useful tool is a clip-on RF current meter. This will tell
you much more than a FS meter, because at last you can *see* where the
RF current is. For details, see my "Best of 'In Practice'" pages or the
MFJ catalog.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Q about balanced feed line
 

Ian White GM3SEK wrote:
Another very useful tool is a clip-on RF current meter. This will tell
you much more than a FS meter, because at last you can *see* where the
RF current is. For details, see my "Best of 'In Practice'" pages or the
MFJ catalog.

I just ordered an MFJ-853 and it's on 2-4 weeks backorder.
--
73, Cecil http://www.qsl.net/w5dxp

Q about balanced feed line
 

On Tue, 28 Feb 2006 04:00:37 -0800, Roy Lewallen
wrote:

Big Endian wrote:

I suppose the right thing to do is to place ferrite cores on all the
conductors in the area. Could get expensive. I have so many wires all
over the place the job seems a bit hopeless.
. . .

Well, that's one way to solve the problem. Like the sign over my desk
says, "Anyone can design a bridge that will stand up. It takes an
engineer to design a bridge that will barely stand up."

Or not [g]

http://www.ketchum.org/bridgecollapse.html

Q about balanced feed line
 

Cecil Moore wrote:
Ian White GM3SEK wrote:
Another very useful tool is a clip-on RF current meter. This will
tell you much more than a FS meter, because at last you can *see*
where the RF current is. For details, see my "Best of 'In Practice'"
pages or the MFJ catalog.

I just ordered an MFJ-853 and it's on 2-4 weeks backorder.

Same story over here - I'm waiting for samples to review for the
magazine.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Q about balanced feed line
 

Wes Stewart wrote:
On Tue, 28 Feb 2006 04:00:37 -0800, Roy Lewallen
wrote:

Big Endian wrote:
I suppose the right thing to do is to place ferrite cores on all the
conductors in the area. Could get expensive. I have so many wires all
over the place the job seems a bit hopeless.
. . .
Well, that's one way to solve the problem. Like the sign over my desk
says, "Anyone can design a bridge that will stand up. It takes an
engineer to design a bridge that will barely stand up."

Or not [g]

http://www.ketchum.org/bridgecollapse.html

Ah, yes, the Tacoma Narrows bridge. That movie played continuously in
the lobby of the Engineering Building at the U. of Colorado most of the
time I was going there. For anyone interested in this topic, I recommend
_To Engineer is Human: The Role of Failure in Successful Design_ by
Henry Petroski.

The whole trick, of course, is to stay on the right side of "barely".

Roy Lewallen, W7EL

Q about balanced feed line
 

Roy Lewallen wrote:
The whole trick, of course, is to stay on the right side of "barely".

Why not the left side? :-)
--
73, Cecil http://www.qsl.net/w5dxp

Q about balanced feed line
 

I keep forgetting some of these principles.

Thanks very much for the detailed and helpful explanations, Roy.

73,

Chuck

Roy Lewallen wrote:
chuck wrote:

As a follow-up, is there a practical way to determine how much current
unbalance will cause a one dB reduction in power delivered to the
antenna, the "lost power" being that power radiated by the
transmission line?

It seems like a rather complex modeling problem.

Thanks!

Chuck, NT3G


Nope. You can't generally say that one part of an antenna is radiating a
particular amount of the total power. Each part of the antenna creates a
field, and it interacts with the fields from all other parts of the
antenna. The total power radiated has to equal the total power input
less loss, but that's all you can say for sure. An example will help
illustrate the problem. Consider a parasitic element in a Yagi. It has
considerable current and contributes a great deal to the overall
pattern. Yet the total power input to the Yagi element is zero. With
zero power input, it can't, by itself, be radiating any power. What it
does is intercept some of the power radiated by the driven element and
re-radiates it with a different phase and amplitude. So how would you
apportion the power radiated by the driven element and the parasitic
element?

You might take a look at the current in the driven element and note that
it increases or decreases as you put the parasitic element in place and
remove it. But the current can either increase or decrease, depending on
the length and spacing of the parasitic element. So has the parasitic
element increased or decreased the power radiated by the driven element?
There's no answer.

You can look at the change in pattern in some idealized cases by
modeling. This can tell you what range of effects you might expect in a
real situation.

Roy Lewallen, W7EL