Does anyone make a 4:1 balun that I can use for an off center fed antenna
that will take the legal limit of power ?

I did find one that is around $ 80 to $ 100 that is suspose to handle it. I
hate to pay that much for a ring of 'iron' and a few feet of wire wound on
it and it will not work.

I have up a home made version of the Carolina Windom. Bought a balun rated
for 1.5 kw. I only run around 1200 watts out of a Drake L4B amp. That
balun will heat up and quit working ( swr goes way up from about 1.7:1 at
the frequency I use most) if I run more than about 500 to 600 watts SSB to
the antenna for any length of time. The antenna is fed with a good grade of
rg8 and about 20 feet from the antenna is a current balun (the one with the
beads over the coax). It will heat up some but when I take it out of the
line, the 4:1 balun still heats up . The 1:1 bead choke does not heat up to
any big ammount when I put it on a dummy load and put 1200 watts to it.

I had a low power balun up with the same antenna and running 100 watts the
antenna seemed to work fine.

If it was not for the wide bandwidth and good results I have been getting ,
I would just run an 80 meter dipole and no balun. Also want an antenna for
40 meters.
Have the usaul triband for 10,15,20.

"Ralph Mowery" wrote in
news
Does anyone make a 4:1 balun that I can use for an off center fed
antenna that will take the legal limit of power ?

Is it too hard to quantify the power limit? It is jurisdiction dependent.

Talking in numbers is the beginning of understanding the problem. (A
loose paraphrasing of Lord Kelvin).

I did find one that is around $ 80 to $ 100 that is suspose to handle
it. I hate to pay that much for a ring of 'iron' and a few feet of
wire wound on it and it will not work.

I have up a home made version of the Carolina Windom. Bought a balun
rated for 1.5 kw. I only run around 1200 watts out of a Drake L4B

The Carolina Windom seems to use a 4:1 voltage balun and a 1:1 current
balun closer to the tx. (I say seems because IIRC it is a proprietary
design.)

The loss in the voltage balun can be expected to be severe when the load
impedance is very high due to the resultant high flux level in the core.

Whilst commercial producers commonly state power limits, and often
extravagantly, few manufacturers give you loss characteristics,
especially for impedances a long way from nominal.

For an experiment, I measured the "heavy duty" 4:1 Ruthroff balun in a
popular 300W rated ATU with a VNA, and calculated efficiency of the balun
feeding a G5RV on five bands. Efficiency of the balun varied from 66% to
almost 100%. (Notes at http://vk1od.net/blog/?p=568 .)

It is my guess that the balun could safely dissipate say 10W continuous.
Then at 66% efficiency, it would only safely accept 30W continuous input.
Fortunately, the peak to average ratio of SSB is something like 30:1, so
it would probably handle 1000W PEP SSB telephony ok.

Rule no 1: Balun manufacturers often supply little information.

Rule no 2: Information that is supplied is of little use in establishing
behaviour on extreme loads.


amp. That balun will heat up and quit working ( swr goes way up from
about 1.7:1 at the frequency I use most) if I run more than about 500
to 600 watts SSB to the antenna for any length of time. The antenna

Using my peak to average ratio, you are talking about an average power of
perhaps 20W.

You have probably reached the Curie point of the core, and it can be
quite low depending on the mix.

It is not unusual that 4:1 voltage baluns that have adequate performance
on a 200 ohm load have efficiency less than 50% on extreme loads such as
might be experienced with the CW.


is fed with a good grade of rg8 and about 20 feet from the antenna is
a current balun (the one with the beads over the coax). It will heat
up some but when I take it out of the line, the 4:1 balun still heats
up . The 1:1 bead choke does not heat up to any big ammount when I
put it on a dummy load and put 1200 watts to it.

The heating of a choke is due to flux cause by common mode current, and
some copper loss. Did your test configuration have zero common mode
current?

Though some show mathematical derivation for the magnitude of common mode
current based on Zo alone (which leads to Rule 500), it is my contention
that approach is not valid in an antenna application, and common mode
current may be much higher or lower than indicated by that method.


I had a low power balun up with the same antenna and running 100 watts
the antenna seemed to work fine.

If it was not for the wide bandwidth and good results I have been
getting , I would just run an 80 meter dipole and no balun. Also want
an antenna for 40 meters.

Don't overlook that a lossy balun leads to lower VSWR, and that is often
erroneously interpreted as an indicator of "good results".

Owen

First thing to remember is a really radical thought: The power rating of a
voltage balun has to be decreased by the highest SWR factor existing on the
line. That is, a 2 kW rated (at 1:1) balun is only good for 1 kW at 2:1
VSWR or 200 watts if your wattmeter shows a 10:1 VSWR looking at the
antenna. The reason is that the current (heating) losses in the windings go
up as the square of the maximum current - remember hearing about "I squared
R". A 4:1 VSWR means the current max value is twice the minimum, therefore
you'll be heating up the core four times as much as if you had a 1:! VSWR on
the line. It doesn't matter whether the line is unbalanced coaxial or
balanced open wire.

In your case the ratio of rated power divided by working power is 1.25, so
the maximum VSWR tolerable before you exceed the dissipation rating of the
balun is only 1.25. Or working the other direction, to always stay cool you
need to find a balun rated for (1200) x (VSWRmax) watts.

The input reactance of the Windom changes as you change the driving
frequency (and band), therefore the VSWR on the feedline does also. The
balun may stay reasonably cool on a few frequencies, but will be flaming hot
on most others.

--
Karl Beckman, P.E.
WA8NVW - licensed since 1964



"Ralph Mowery" wrote in message
news
Does anyone make a 4:1 balun that I can use for an off center fed antenna
that will take the legal limit of power ?

I did find one that is around $ 80 to $ 100 that is suspose to handle it.
I hate to pay that much for a ring of 'iron' and a few feet of wire wound
on it and it will not work.

I have up a home made version of the Carolina Windom. Bought a balun
rated for 1.5 kw. I only run around 1200 watts out of a Drake L4B amp.
That balun will heat up and quit working ( swr goes way up from about
1.7:1 at the frequency I use most) if I run more than about 500 to 600
watts SSB to the antenna for any length of time. The antenna is fed with
a good grade of rg8 and about 20 feet from the antenna is a current balun
(the one with the beads over the coax). It will heat up some but when I
take it out of the line, the 4:1 balun still heats up . The 1:1 bead
choke does not heat up to any big ammount when I put it on a dummy load
and put 1200 watts to it.

I had a low power balun up with the same antenna and running 100 watts the
antenna seemed to work fine.

If it was not for the wide bandwidth and good results I have been getting
, I would just run an 80 meter dipole and no balun. Also want an antenna
for 40 meters.
Have the usaul triband for 10,15,20.

Karl Beckman wrote:
First thing to remember is a really radical thought: The power rating of a
voltage balun has to be decreased by the highest SWR factor existing on the
line. That is, a 2 kW rated (at 1:1) balun is only good for 1 kW at 2:1
VSWR or 200 watts if your wattmeter shows a 10:1 VSWR looking at the
antenna. The reason is that the current (heating) losses in the windings go
up as the square of the maximum current - remember hearing about "I squared
R". A 4:1 VSWR means the current max value is twice the minimum, therefore
you'll be heating up the core four times as much as if you had a 1:! VSWR on
the line. It doesn't matter whether the line is unbalanced coaxial or
balanced open wire.


The other factor is core saturation.. flux goes as the voltage*frequency
.... so 10:1 VSWR means you might have 10x voltage..

On Tue, 22 Sep 2009 09:52:46 -0700, Jim Lux
wrote:

The other factor is core saturation..

Hi Jim,

The only reason why a common mode choke (a more appropriate BalUn
construction for any application) would encounter "core saturation" is
due to the presence of a very significant common mode current - the
thing the choke (or BalUn) is supposed to suppress. If the "core
saturates" this is an indication that a common mode choke is very,
very necessary.

The better the choke (the higher its common mode Z), the more it will
snub the current. The more it snubs the current, the less chance of
"core saturation."

The solution to a hot BalUn is suppression of the current that is
energizing the "core."

As for:
Karl Beckman wrote:
First thing to remember is a really radical thought: The power rating of a
voltage balun has to be decreased by the highest SWR factor existing on the
line.

I have NEVER heard this apocryphal "rule of thumb" before. For one
thing, it doesn't make sense on the face of it as it defines a linear
relationship between current (or voltage) with power.

73's
Richard Clark, KB7QHC

Jim Lux wrote:

The other factor is core saturation.. flux goes as the voltage*frequency
... so 10:1 VSWR means you might have 10x voltage..

At HF, the ferrites which are best to use for baluns will go up in
flames due to loss at flux densities well below saturation.

Roy Lewallen, W7EL

"Karl Beckman" wrote in
:

First thing to remember is a really radical thought: The power rating
of a voltage balun has to be decreased by the highest SWR factor
existing on the line. That is, a 2 kW rated (at 1:1) balun is only
good for 1 kW at 2:1 VSWR or 200 watts if your wattmeter shows a 10:1
VSWR looking at the antenna. The reason is that the current (heating)
losses in the windings go up as the square of the maximum current -
remember hearing about "I squared R". A 4:1 VSWR means the current
max value is twice the minimum, therefore you'll be heating up the
core four times as much as if you had a 1:! VSWR on the line. It
doesn't matter whether the line is unbalanced coaxial or balanced open
wire.

My comments are addressed to so called voltage baluns. The above
explanation and my comments are not applicable to current baluns.

Your explanation of your Rule of Thumb is valid if the balun is located
at an impedance minimum for the stated VSWR. The explanation does not
apply at all in the opposite case, and to a lesser extent in all other
cases.

In many cases where the balun overheats, it is operating at an extremely
high current, and I^2R losses are not main contribution to heating.


In your case the ratio of rated power divided by working power is
1.25, so the maximum VSWR tolerable before you exceed the dissipation
rating of the balun is only 1.25. Or working the other direction, to
always stay cool you need to find a balun rated for (1200) x (VSWRmax)
watts.

Which also assumes that the balun was properly rated for the 1200W.


The input reactance of the Windom changes as you change the driving
frequency (and band), therefore the VSWR on the feedline does also.
The balun may stay reasonably cool on a few frequencies, but will be
flaming hot on most others.


The core material may only need to reach temperatures towards 200°C to
compromise the balun, the Curie point of some ferrites in use is lower
than 200°C. Thing is that the ferrite heats very slowly, and a 5 minute
test is not likely to raise the temperature to anywhere near the long
term temperature. That is good for us for many modes as they have high
peak to average ratio, but for the low peak to average modes / high duty
cycle modes, the balun core may increase in temperature significantly for
an hour.

The key thing is that assuming balun efficiency is very high is quite
wrong, and when you start to think about balun efficiencies being below
50% under some extreme conditions, you realise the challenge in 5kW rated
devices that are in small boxes and must not reach 200°C.

Owen

Roy Lewallen wrote:
Jim Lux wrote:

The other factor is core saturation.. flux goes as the
voltage*frequency ... so 10:1 VSWR means you might have 10x voltage..

At HF, the ferrites which are best to use for baluns will go up in
flames due to loss at flux densities well below saturation.

Roy Lewallen, W7EL


Well then, same general idea.. lots of volts = lots of flux = lots of
dissipated energy from the core loss...

And, of course, not all baluns are made with appropriate materials (e.g.
using a lossy EMI suppression mix might be fine in a "choke"
application, where high Z is keeping the current low.. but terrible in a
transformer type situation, where you have a lot of flux in the core)

On Tue, 22 Sep 2009 14:44:39 -0700, Jim Lux
wrote:

And, of course, not all baluns are made with appropriate materials (e.g.
using a lossy EMI suppression mix might be fine in a "choke"
application, where high Z is keeping the current low.. but terrible in a
transformer type situation, where you have a lot of flux in the core)

Hi Jim,

A BalUn IS a transformer, and many of the lowest loss, widest
bandwidth ones are specifically designed to choke common mode
currents.

Such BalUns are NOT flux linked transformers and thus avoid working
(transverse) currents inducing loss and saturation issues.

It appears that the inference from your flux transformer terminology
transformer type situation, where you have a lot of flux in the core)
is at cross purposes with BalUn best design.

73's
Richard Clark, KB7QHC

Jim Lux wrote:
Roy Lewallen wrote:
Jim Lux wrote:

The other factor is core saturation.. flux goes as the
voltage*frequency ... so 10:1 VSWR means you might have 10x voltage..

At HF, the ferrites which are best to use for baluns will go up in
flames due to loss at flux densities well below saturation.

Roy Lewallen, W7EL


Well then, same general idea.. lots of volts = lots of flux = lots of
dissipated energy from the core loss...

Not exactly. The dominant loss mechanisms in "low frequency" ferrites
are essentially linear, and don't cause distortion. Saturation occurs
during a portion of each cycle, resulting in distortion. And saturation
doesn't always imply high loss.

And, of course, not all baluns are made with appropriate materials (e.g.
using a lossy EMI suppression mix might be fine in a "choke"
application, where high Z is keeping the current low.. but terrible in a
transformer type situation, where you have a lot of flux in the core)

A properly designed transformer has very little flux in the core -- the
flux is the vector sum of the flux in all the windings, which in an
ideal transformer is zero. The flux you do have is the magnetizing flux
due to the finite impedances of the windings, which you strive to
maximize just as you do in a choke (and the leakage flux which isn't
coupled from one winding to the others). So the best core material is
generally the same for a broadband choke as it is for a broadband
transformer. EMI suppression materials are very good for both, since
they're engineered to maximize impedance. An exception is where you're
dealing with enough power that the core loss is intolerable. For
example, a well designed choke or transformer might have only 0.5 dB
loss, a generally insignificant amount. But if you apply a kW to it,
you're talking about 120 watts of power dissipation, too much for a
small core. In those cases you have to use lower loss material, which
usually means lower impedance windings and consequent higher flux density.

Roy Lewallen, W7EL