Add that 4 ounces to the weight of 50 feet of coax.
then subtract the weight of 50 feet of balanced line
that is a larger difference

"Dan Richardson arrl net" k6mheatdot wrote in message
...
On Sun, 26 Jun 2005 14:19:30 -0400, "Hal Rosser"
wrote:

The only thing I have against them (current baluns) is
They are heavy.
and cause the antenna to droop
lowering the height of the feedpoint.
Which is a good reason to put the balun near the radio and use balanced
feedline from there to the antenna
my 3.5 cents


I just weighed 50 beads that are used in W2DU's balun and came up with
a whopping 4 ounces!

Yea, four ounces should cause one hell of a droop.G

73,
Danny, K6MHE

In your original post you said:

"The only thing I have against them (current baluns) is
They are heavy.
and cause the antenna to droop lowering the height of the feedpoint."

Anyway, with say fifty pounds of tension just how much drop are you
talking about? And what difference does it make?




On Sun, 26 Jun 2005 17:11:43 -0400, "Hal Rosser"
wrote:

Add that 4 ounces to the weight of 50 feet of coax.
then subtract the weight of 50 feet of balanced line
that is a larger difference

"Dan Richardson arrl net" k6mheatdot wrote in message
.. .
On Sun, 26 Jun 2005 14:19:30 -0400, "Hal Rosser"
wrote:

The only thing I have against them (current baluns) is
They are heavy.
and cause the antenna to droop
lowering the height of the feedpoint.
Which is a good reason to put the balun near the radio and use balanced
feedline from there to the antenna
my 3.5 cents


I just weighed 50 beads that are used in W2DU's balun and came up with
a whopping 4 ounces!

Yea, four ounces should cause one hell of a droop.G

73,
Danny, K6MHE

On Sun, 26 Jun 2005 13:37:46 +0000 (UTC), "Reg Edwards"
wrote:


Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?

Reg, I haven't measured it, however...

I am in the process of modeling a balun as follow up on my G5RV feed
systems analysis. The scenario is a G5RV at 10m centre height, a
vertical drop of open wire line (the so called "matching section") and
a balun at near ground height (with unbalanced shunt admittance
introduced by the balun to ground).

I have been jiggling the unbalanced shunt admittance introduced by the
balun and observing the current through that admittance wrt the
feedline currents, and the apparent distortion of the radiation
pattern. I could nearly as easily have been comparing the current in
one of the wires of the feedline wrt the other, it is just the format
of the currents report that makes the former easier. Another
interesting observation would be the changes to receive sensitivity to
vertically polarised waves (indicating possible feedline pickup).

The models indicate a few things so far:
- the effect of the balun is on the unbalance current distribution on
the whole feedline;
- current imbalance at the base of the "matching section" of better
than about -15dB caused little distortion of the pattern on 20m and
below;
- some configurations seem quite undesirable in terms of pattern
distortion even though balun current is quite low;
- raising the antenna / feedline / balun and lengthening the earth
connection from the balun shunt admittance changes the current
distribution.

This leads me to think that measurement of the imbalance current at a
single point might not give the "big picture". I found scenarios where
inserting an imperfect balun increased the current at a point (it
changed the magnitude of the standing wave and more importantly moved
the current minimum), so I could see someone with a handy-dandy
current probe measuring such a situation and insisting they have proof
the baluns don't "work".

Owen
--

What impedance ratio are you interested in? Reason for asking is that
when I was looking for prior art on current baluns I came across a very
interesting 1:1 design that uses two equal length pieces of coax that would
each be less than an eighth of a wavelength long and which has a very wide
bandwidth. I copied the schematic (which has a slight error) and the photo
to a single sheet PDF file if anyone's interested.

Chris

,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
_ |/ Principal Engineer
oo\ Sonoran Radio Research
(__)\ _ P.O. Box 25240
\ \ .' `. Tempe, Arizona 85285-5240
\ \ / \
\ '" \ IEEE Senior Member #40274515
. ( ) \
'-| )__| :. \ Email:
| | | | \ '. http://www.home.earthlink.net/~christrask
c__; c__; '-..'.__

Graphics by Loek Frederiks

"Reg Edwards" wrote in message
...
A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?
----
Reg.

"Dan Richardson arrl net" k6mheatdot wrote in message
...
In your original post you said:

"The only thing I have against them (current baluns) is
They are heavy.
and cause the antenna to droop lowering the height of the feedpoint."

Anyway, with say fifty pounds of tension just how much drop are you
talking about? And what difference does it make?


Apparently it makes more difference to me than it does to you.
I don't want it digging into the tree branches.
Nothing wrong with your view - its probably a better-informed view than
mine - but I'll still use balanced line and I still think baluns are too
heavy. I'm just hard-headed that way. :-)

On Sun, 26 Jun 2005 13:37:46 +0000 (UTC), "Reg Edwards"
wrote:

A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?
----
Reg.


I ran across an article on choke baluns recently in the 2004 ARRL
handbook. It said ( as best as I can recall ) that "purists" might
argue for the use of a choke balun for dipoles for the optimum
radiation pattern, but that most dipoles weren't high enough off the
ground to have a "correct" pattern anyway, so their use for optimum
radiation patterns is questionable at best. Keeping RF out of the
shack might be a different story ? I used a coaxial choke balun on my
G5RV but I don't use either a coaxial choke balun or a commercial
balun on either my 40 meter dipole ( too heavy, the dipole is
constructed out of 18 Ga wire ) or my 30 meter dipole. I was too lazy
to go through all the hassles of either wiring up a PL connector for
the commercial choke balun I have and I didn't want to wind up several
feet of coax for a coaxial balun ( weight and sag issues again )

YMMV

Gary

Hal Rosser wrote:

Apparently it makes more difference to me than it does to you.
I don't want it digging into the tree branches.
Nothing wrong with your view - its probably a better-informed view than
mine - but I'll still use balanced line and I still think baluns are too
heavy. I'm just hard-headed that way. :-)


Unfortunately, using "balanced" (symmetrical) line doesn't prevent or
reduce feedline radiation. It's subject to the same effects as coax. The
only difference is where it happens. Conducted common mode current is
explained in http://eznec.com/Amateur/Articles/Baluns.pdf. As for
current induced by mutual coupling, both types of feedline will have the
same amount of induced common mode current, due to the same cause and
having the same effect.

It's not the geometry of the feedline that causes or prevents feedline
radiation.

Roy Lewallen, W7EL

Owen wrote:
. . .
This leads me to think that measurement of the imbalance current at a
single point might not give the "big picture". I found scenarios where
inserting an imperfect balun increased the current at a point (it
changed the magnitude of the standing wave and more importantly moved
the current minimum), so I could see someone with a handy-dandy
current probe measuring such a situation and insisting they have proof
the baluns don't "work".

This situation lends itself well to modeling, where it's readily
illustrated. While it's often difficult to exactly model a given
physical setup, modeling allows us to control the variables and clearly
see what's happening. We can often apply this knowledge and insight to
real situations.

Roy Lewallen, W7EL

Hal Rosser wrote:

"Dan Richardson arrl net" k6mheatdot wrote in message
.. .
In your original post you said:

"The only thing I have against them (current baluns) is
They are heavy.
and cause the antenna to droop lowering the height of the feedpoint."

Anyway, with say fifty pounds of tension just how much drop are you
talking about? And what difference does it make?


Apparently it makes more difference to me than it does to you.
I don't want it digging into the tree branches.

That's a fair point. The sag in a dipole supported only at the ends is
very sensitive to the suspended weight in the middle. And if the end
supports are trees, the problem can become extreme.

Nothing wrong with your view - its probably a better-informed view than
mine - but I'll still use balanced line and I still think baluns are too
heavy. I'm just hard-headed that way. :-)

If sag is a problem, don't use 300 or 450-ohm ladder line. In terms of
weight and windage, it is a very bad solution. A much more practical
solution is to make your own ultra-lightweight parallel line. The wire
can be much thinner than the main antenna, and you can use a spacing of
several inches with the absolute minimum number of ultra-lightweight
spreaders.


But more important than that, please stop calling it "balanced line".
Somehow we have got into the habit of kidding ourselves that
parallel-wire line is balanced line. It isn't!

Parallel line does NOT automatically balance itself. It will cheerfully
allow unequal currents on the two wires. That's the same as saying it
will cheerfully support an unwanted common-mode current (same magnitude
and same direction on both wires) in addition to the wanted
equal-and-opposite currents.

So parallel line will NOT be balanced line - not until you have done
something to MAKE it balanced.

The one best way to create a balanced feedline is to make the layout of
the antenna and feedline is completely symmetrical with respect to
ground - and that includes the entire run of feedline back to the shack.
Unless you have taken the trouble to do that, you WILL have common-mode
currents on the line and it WON'T be balanced. The common-mode current
may not be large enough to cause a practical problem... but don't ever
kid yourself that it isn't there.

Because it's difficult to use a choke balun with parallel-wire line, and
because of the weight problem, about the only practical place where you
can stop common-mode currents is at ground level. A choke or a
link-coupled ATU will force a minimum in the common-mode current at that
position; but a quarter-wavelength up the line towards the antenna, it
will also force a maximum in the common-mode current (and if the line is
long enough, these maxima will repeat every half-wavelength). With
parallel-wire feedline, your only defence against that problem is a
symmetrical layout.



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

On Mon, 27 Jun 2005 00:33:52 -0700, Roy Lewallen
wrote:

Owen wrote:
. . .
This leads me to think that measurement of the imbalance current at a
single point might not give the "big picture". I found scenarios where
inserting an imperfect balun increased the current at a point (it
changed the magnitude of the standing wave and more importantly moved
the current minimum), so I could see someone with a handy-dandy
current probe measuring such a situation and insisting they have proof
the baluns don't "work".

This situation lends itself well to modeling, where it's readily
illustrated. While it's often difficult to exactly model a given
physical setup, modeling allows us to control the variables and clearly
see what's happening. We can often apply this knowledge and insight to
real situations.


Exactly. Nothing I wrote was intended to comment adversely on your
quoted paper, it is interesting and relevant... just a pity the
results tables are not 100% legible.

Modeling shows me the risks of single point measurement, and I agree
entirely with your final statement "While it's often difficult to
exactly model a given physical setup, modeling allows us to control
the variables and clearly see what's happening. We can often apply
this knowledge and insight to real situations". A whole lot of insight
can be gained in a very short time.

Owen

--