what a 1:1 choke balum used for
 

wrote:
John Popelish wrote:

rocky wrote:

To sort of sum things up, then what should I use for a choke balun on
75 meters, 77, 73 or 43 mix? More the better? I read the W2DU article
and he used 73, but I thought 77 may be better?

If you are going to have to go out and buy the cores, type 43 (and its
competitors) is way more common and cheap than any of the others. It
is also readily available in long form toroids called shield beads.


You are going to get into trouble with the W2DU balun at high power
levels or with high commonn mode voltages across the balun. Each bead
suggested is only good for about 1/2 watt dissipation in open air
during long duty cycle.

I assume you are talking about the beads mentioned in this document:
http://www.w2du.com/r2ch21.pdf

At the bottom of page 21-6, he says that the beads have a .197 inch
hole and are .190 inch long.

The beads I am suggesting are over an inch in diameter and over an
inch long. A half watt would barely raise their temperature
noticeably above ambient. And they will fit over coax that is a half
inch in diameter. There are other shapes that are more cost effective
for smaller diameter coax. 28B0591-200 has a .23 inch hole, but is
1.38 inches long, with a .591 inch OD. A half watt won't warm that
one very much, either. And it costs only $.76 each, if you buy 10 of
them.

My point was that there are cheap long form factor toroids available
now, that weren't available when W2DU designed and described his BalUn.

Also, a string of beads is a terribly inefficient use of ferrite
materials. If you double the expense of the balun by doubling the
number of beads, you only double the common mode impedance.

But it spreads the heat out, and doesn't require you to kink the coax,
which makes it last longer in the weather. If you want to wind large
diameter toroids, they now make low cost versions of these for EMI
purposes, also. For example Steward # 28B2400-000, outside diameter
2.4 inches OD, 1.4 inch ID, .5 inch thick costs only $3.36 at Digikey,
quantity 1. Again, Steward type 28 is roughly similar to Fair-Rite
type 43.

If you use a less resistive material with lower loss tangent and
multiple turns through the core, you can greatly increase power
capacity and choking impedance with much less increase in cost.

Yes, the turns squared effect makes better use of the mass of the
ferrite to produce impedance.

what a 1:1 choke balum used for
 

Roy Lewallen wrote:
John Popelish wrote:

. . .
As I understand common mode current, it is the net imbalance between
the current through the center conductor and the current through the
shield.


If you consider the sum of the physically separate currents on the
inside and outside of the shield to be the current "through the shield",
that's correct. And it's equal to the current on the outside of the shield.

Yes, I was calling the sum of the currents on the inside and outside
of the shield, the current through the shield. Sorry, if that is a no no.

what a 1:1 choke balum used for
 

On Wed, 29 Mar 2006 17:50:28 -0500, John Popelish
wrote:

Richard Clark wrote:
On Wed, 29 Mar 2006 17:30:54 -0500, John Popelish
wrote:


Richard Clark wrote:
(snip)

#64 material is going to offer about 3 Ohms per bead;
#43 material is going to offer about 8 Ohms per bead;
#73 & 77 material is going to offer about 18 Ohms per bead;
#75 material is going to show offer 28 Ohms per bead.

(snip)

What dimension cores produce these impedances at 75 meters?


Hi John,

It is called a 101 sized bead:
.138" OD
.051" ID
.128" high

Are these what you recommend as coax choke balun beads? That is some
fine coax.

Hi John,

I do use some small stuff, like RG-174 and precision hard line, but
you are right, this is not for RG-58 which I commonly use. The 101
size is Amidon's reference for a multiplier for other forms.

73's
Richard Clark, KB7QHC

what a 1:1 choke balum used for
 

The choke impedance is inductive at low frequencies. Loss in the
ferrite material is low.

But due to a lossy ferrite material at the higher frequencies the
equivalent circuit is the inductance in parallel with a high
resistance.

At sufficiently high frequencies the choke impedance is almost a pure
high resistance. Which chokes the current just as well as a high
inductive reactance.

This is all that's necessary to explain the operation of a choke
balun.

I can't imagine why you are all making such a fuss about it.
----
Reg.

what a 1:1 choke balum used for
 

On Thu, 30 Mar 2006 01:32:10 +0100, "Reg Edwards"
wrote:

I can't imagine why you are all making such a fuss about it.

Reggie,

There's no way you can convince us you lack imagination.

73's
Richard Clark, KB7QHC

what a 1:1 choke balum used for
 

Richard Clark wrote:

I do use some small stuff, like RG-174 and precision hard line, but
you are right, this is not for RG-58 which I commonly use. The 101
size is Amidon's reference for a multiplier for other forms.

I wind about 10 turns of RG-174 type coax on a core having an OD of a
bit more than an inch. Works fine up to at least 300 watts with a
reasonably matched antenna.

Roy Lewallen, W7EL

what a 1:1 choke balum used for
 

rocky wrote:
You would use physically larger cores of 43 material and more turns in
the core for say 75 M in a choke balun?

Sure.

The problem actually all comes down to the common mode current flowing
through the beads, and that's the same as looking at voltage across the
shield from one end to the other of the "choke".

Some antennas, even with very low power and 50 ohm feedpoints, will
produce fairly high across the string of beads. This can cause quite a
bit of heating, and cause the feedline to remain part of the radiating
system despite the use of a balun.

In controlled situations strings of beads work pretty well. In other
cases they are totally inadequate, and the problem can have nothing to
do with the impedance across the feedline (SWR).

I never use strings of beads on my antennas.

73 Tom

what a 1:1 choke balum used for
 

John Popelish wrote:
The beads I am suggesting are over an inch in diameter and over an
inch long. A half watt would barely raise their temperature
noticeably above ambient. And they will fit over coax that is a half
inch in diameter. There are other shapes that are more cost effective
for smaller diameter coax. 28B0591-200 has a .23 inch hole, but is
1.38 inches long, with a .591 inch OD. A half watt won't warm that
one very much, either. And it costs only $.76 each, if you buy 10 of
them.

My point was that there are cheap long form factor toroids available
now, that weren't available when W2DU designed and described his BalUn.

My point is dollar for dollar multiple turns always wind up being a
better investment. That's because impedance approximately follows the
square of the passes through the core.

Also, a string of beads is a terribly inefficient use of ferrite
materials. If you double the expense of the balun by doubling the
number of beads, you only double the common mode impedance.

But it spreads the heat out, and doesn't require you to kink the coax,
which makes it last longer in the weather.

I've never once had cable fail from being wound on cores. I can't
imagine why someone would need to kink the cable.

The only part of the cable that significantly increases CM impedance is
the part inside the core window. Why care how tightly the cable is
pulled against the core outside??

73 Tom

what a 1:1 choke balum used for
 

what a 1:1 choke balum used for
 

John Popelish wrote:
wrote:
I've never once had cable fail from being wound on cores. I can't
imagine why someone would need to kink the cable.

I just found this rule of thumb that says coax should not be bent to a
radius smaller than 6 times the cable diameter.
http://www.wiremold.com/www/commerci...dex.asp?wpid=4

For RG-58 this comes out to about a 1.2 inch bend radius.

This spec for RG 58:
http://www.pacificcable.com/Picture_...?DataName=RG58
Specifies 1.25 inch minimum bend radius, only if there is no pull on
the cable. If the cable is tension loaded, they recommend it be
wrapped over a minimum 2.5 inch radius form.

That would get to be a pretty big coil on a toroid.

what a 1:1 choke balum used for
 

"John Popelish" wrote in message
...
wrote:
John Popelish wrote:

SNIP
At low frequency, I understand how this is a good approach (though this
discussion was about the W2DU style choke balun). But at higher
frequencies, I am concerned that the turn to turn capacitance might
provide a low impedance path that parallels the choke. A string of beads
does not have this problem.


Hi John

"For what its worth", I have wounf the coax around a single ferrite toroid
with the exact amount of turns and spacing so the impedance along the
conductor of the coax outer shield was maximum, as in parallel resonance.
I cant claim that it does any better job than any other "1:1 balun", but it
worked for me.
My point is - The turn to turn "stray" capacitance doesnt necessarily have
to be a source of performance degradation.

Jerry

what a 1:1 choke balum used for
 

Jerry Martes wrote:
"John Popelish" wrote in message
...

wrote:

John Popelish wrote:


SNIP

At low frequency, I understand how this is a good approach (though this
discussion was about the W2DU style choke balun). But at higher
frequencies, I am concerned that the turn to turn capacitance might
provide a low impedance path that parallels the choke. A string of beads
does not have this problem.



Hi John

"For what its worth", I have wounf the coax around a single ferrite toroid
with the exact amount of turns and spacing so the impedance along the
conductor of the coax outer shield was maximum, as in parallel resonance.
I cant claim that it does any better job than any other "1:1 balun", but it
worked for me.
My point is - The turn to turn "stray" capacitance doesnt necessarily have
to be a source of performance degradation.

I think of it as more of a upper limit. Once you are above resonance,
the choke action has to drop. And if you are using one of the low
frequency ferrites, the resonance isn't going to be anything to write
home about either. ;-)

what a 1:1 choke balum used for
 

"John Popelish" wrote in message
...
Jerry Martes wrote:
"John Popelish" wrote in message
...

wrote:

John Popelish wrote:


SNIP

At low frequency, I understand how this is a good approach (though this
discussion was about the W2DU style choke balun). But at higher
frequencies, I am concerned that the turn to turn capacitance might
provide a low impedance path that parallels the choke. A string of beads
does not have this problem.



Hi John

"For what its worth", I have wounf the coax around a single ferrite
toroid with the exact amount of turns and spacing so the impedance along
the conductor of the coax outer shield was maximum, as in parallel
resonance. I cant claim that it does any better job than any other "1:1
balun", but it worked for me.
My point is - The turn to turn "stray" capacitance doesnt necessarily
have to be a source of performance degradation.

I think of it as more of a upper limit. Once you are above resonance, the
choke action has to drop. And if you are using one of the low frequency
ferrites, the resonance isn't going to be anything to write home about
either. ;-)


Hi John

I am not smart enough to be able to give instructions to *anyone*. But, I
have thought of "hi Q" resonance something I want to avoid anyway in making
a Balun. I was worried that a high Q resonant circuit without sisnificant
loss might assist coupling to the feed line if/when that feed line was close
to some multiple of a half wave.

Anyway, you get the idea I was trying to address concerning any worry
about stray capacitance ruining the Balun performance.

Jerry

what a 1:1 choke balum used for
 

John Popelish wrote:
At low frequency, I understand how this is a good approach (though
this discussion was about the W2DU style choke balun). But at higher
frequencies, I am concerned that the turn to turn capacitance might
provide a low impedance path that parallels the choke. A string of
beads does not have this problem.

Not a valid point.

Say we have 1000 ohms XL in parallel with 1000 ohms Xc at 10MHz. At 14
MHz we have 1400 ohms XL in parallel with 714 ohms Xc. The combined
reactance is just over 1400 ohms.

Capacitive reactance in parallel with inductive reactance increases the
impedance, until we are over 1.414 times the resonant frequency.
Anyplace below that, the shut C decrases unwanted coupling.

If you look at actual chokes, you'll see that is a totally unfounded
concern at HF.

That toroid showing the flipped winding that is supposed to reduce
stray C? It actually makes a choke work slightly worse...not
bettter...until we get way up in VHF or UHF.

I always try to not bend any cable to a smaller radius than the
manufacturer recommends, and I am not familiar with this
recommendation for common coax types used by amateurs. I would have
to look that up before wrapping a core.

Manufacturers are very conservative. I use RG400 in very tight coils
without any issue, and my main baluns are all air core RG213, LMR400,
or RG8X. I do some very tight radius bends without problems. My 160
vertical array uses a phase inverting transformer made with RG-400, and
it is two parallel 3" tall stacks of 61 material 2" OD cores wound as
tight as possible with RG-303. It handles huge voltage across the
winding without any issues.

The only part of the cable that significantly increases CM impedance is
the part inside the core window. Why care how tightly the cable is
pulled against the core outside??

The weight of the cable will tighten the turns on the core.

Simple to fix. Don't hang anything from the cable leaving the core.

I have over 300 feet of RG8X hanging vertically from a high dipole, but
I have a rope lacing the cable as a strain relief. Been up since 1999.

73 Tom

what a 1:1 choke balum used for
 

what a 1:1 choke balum used for
 

http://www.w8ji.com/toroid_balun_winding.htm

73 Tom

which brand?what a 1:1 choke balum used for
 

In article ,
Cecil Moore wrote:

Roy Lewallen wrote:
So any core you put over the coax doesn't
see or interact with the common mode current or its fields at all, and
you can completely ignore it when analyzing balun action.

Roy probably meant "differential" above instead of "common".
Cores on coax definitely "interact with the common mode current
or its fields" and that is their purpose.

ok so after reading all this, wich i enjoyed, confused me a bit.

lets say i operate 10-160m and 6m (all band antenna)
, at max 500wout. (typically 200w)

who makes a good commercial choke balun"" w/so239's at the ends??


make/model/where to buy, ??


i've been using a w2du, lots have told me it's not the 'best' money
isn't the issue i'd just like to get a 'good one' ie efficient


thanks

any tips appreciated

which brand?what a 1:1 choke balum used for
 

ml wrote:
In article ,
Cecil Moore wrote:

Roy Lewallen wrote:
So any core you put over the coax doesn't
see or interact with the common mode current or its fields at all, and
you can completely ignore it when analyzing balun action.
Roy probably meant "differential" above instead of "common".
Cores on coax definitely "interact with the common mode current
or its fields" and that is their purpose.

Indeed I did. I apologize for the error.

Roy Lewallen, W7EL