"dbc254" wrote in message
...
Everyone makes fun of newbies buying ready-built dipoles on eBay, but
nobody can direct you to where to buy baluns? Searched hi and lo
online, and what I found, was more expensive than buying a ready-made
dipole! I'd like to buy a balun, and attach my own cut-to-length
wire, but can't find cheap baluns ANYWHERE.

Where are you Elmers buying your baluns?

you have coax? split one end, connect center conductor to one wire, shield
to the other. wind a bunch of turns (there is a web site somewhere with
numbers) around a piece of pvc pipe, and voila, instant balun. you want to
pay for off the shelf stuff, expect to pay for the ferrites that can handle
1500w all the way down to 160m, plus construction, packaging, shipping, and
marketting... that stuff is more expensive than the rest of the antenna.

want to be even cheaper? use twin lead, connect it directly to the wire and
run it down to a tuner that includes a balun... do it all in one place with
less loss.

"Dave" wrote in message
news:nlktk.864$UX.475@trnddc03...

"dbc254" wrote in message
...
Everyone makes fun of newbies buying ready-built dipoles on eBay, but
nobody can direct you to where to buy baluns? Searched hi and lo
online, and what I found, was more expensive than buying a ready-made
dipole! I'd like to buy a balun, and attach my own cut-to-length
wire, but can't find cheap baluns ANYWHERE.

Where are you Elmers buying your baluns?

you have coax? split one end, connect center conductor to one wire,
shield to the other. wind a bunch of turns (there is a web site somewhere
with numbers) around a piece of pvc pipe, and voila, instant balun. you
want to pay for off the shelf stuff, expect to pay for the ferrites that
can handle 1500w all the way down to 160m, plus construction, packaging,
shipping, and marketting... that stuff is more expensive than the rest of
the antenna.


Price the 20 or 30 feet of coax to wind the balun (choke) and it may be
cheeper to buy a balun.

I don't see wasting time or money on a balun for just a simple dipole .
Sure it may make the patern vary from the normal textbook, but who cares
most of the time. Most people have to put the antenna up wherever they can
and lots of time it is not in the desired direction anyway.

NOw a beam or some other antenna design is differant.

Ralph Mowery wrote:

I don't see wasting time or money on a balun for just a simple dipole
. Sure it may make the patern vary from the normal textbook, but who
cares most of the time. Most people have to put the antenna up
wherever they can and lots of time it is not in the desired direction
anyway.

Very often, those are the same people who complain of "poor conditions"
and "noisy bands", and operate in constant fear of causing RFI. Many of
these problems are simply due to common-mode feedline currents bringing
RF back into the shack and coupling into the mains wiring.

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.

The problems of desperate antenna locations cannot be entirely cured,
but they *can* be improved. Almost always, feedline chokes and/or baluns
will have a valuable part to play.

NOw a beam or some other antenna design is differant.

The largest difference is in the attitudes of the users. No matter what
your antenna is, or where you're forced to install it, it all comes down
to one simple question: do you want to give this antenna the best
possible chance to work correctly... or not?



--

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

Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains. A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow. I agree that the effect is
the same, semantically, ie one side effect of the use of a balun is
less CM interference from coming down a balanced feedline but it is
there for a different reason.

Dan

On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.

Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.

Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

And also, what exactly do you mean by "balanced" in the context of a
feedline?

I agree that the effect is
the same, semantically, ie one side effect of the use of a balun is
less CM interference from coming down a balanced feedline but it is
there for a different reason.

Not in my station. My motivation for using common-mode chokes is
*specifically* to control any incoming and outgoing interference that
may be caused by common-mode currents on the feedline.

When the common-mode component of the feedline is reduced, it will also
be accompanied by an improvement in "balance" on the antenna, because
the two things go together (or at least, they do for some definitions of
that word). But "balance" is never my primary goal because I don't find
the concept helpful, either when deciding what to do next or when
evaluating the results.



--

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

On Aug 31, 3:07*pm, Ian White GM3SEK wrote:
Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.
Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. *A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition *of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A common mode choke is used in RF applications, very true, but it
serves a filtering purpose,
not a conversion of unbalanced to balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..


A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

You do not want the balun to operate hot (ir to dissipate heat as you
do with a CM choke filter). You strive for 100% transfer of energy and
settle for the best
you can get. With a CM choke, you try to filter and dissipate unwanted
back-RF. Any back RF from your balun
should be converted to unbalanced transfer back to the source. You
reduce back-RF by matching impedances (which can also involve baluns
but not the 1:1 application discussed here). If you try to filter it
the unwanted back-RF, you will also end up filtering the forward
energy transfer. Of course, that would be an undersirable situation.


And also, what exactly do you mean by "balanced" in the context of a
feedline?

For a 2 conductor feedline, the V in each conductor is 180 degrees out
of phase with each other. Same with I. One conductor is +90 degrees
and the other is -90 degrees with respect to earth. At any given
instant and location the summation of both conductors with respect to
each other is equal to the magnitude it would be on the inner
conductor on the unbalanced (coax) with respect to ground (shield).
Since magnitude of the V on each conductor of the balanced line are
equal and opposite in phase, the term "balanced" is appropriate. Same
with I.



I agree that the effect is
the same, semantically, ie one side effect of the use of a balun is
less CM interference from coming down a balanced feedline but it is
there for a different reason.

Not in my station. My motivation for using common-mode chokes is
*specifically* to control any incoming and outgoing interference that
may be caused by common-mode currents on the feedline.

Of course. But it is not due to filtering unwanted RF, it is due to
the conversion of balancing your energy so
that the coax properly acts as a shielded unbalanced line with no
energy in the shield and all energy in the inner conductor
(assuming perfect conditions). Your dipole will try to balance when
fed as a dipole directly from a coax.. Without the balun, any
reflected energy will
partially come down the shield to ground causing interference. The
balun simply unbalances the reflected energy, if any, to that it all
returns through
the inner conductor eliminating RFI if the radio and the shield are
properly earthed.


When the common-mode component of the feedline is reduced, it will also
be accompanied by an improvement in "balance" on the antenna, because
the two things go together (or at least, they do for some definitions of
that word).

But think of your dipole as a balanced transmission line. That's what
it is, with a lot of loss (into radiation resistance).
You WANT common mode on THAT that lossy transmission line and you do
not want it filtered away.

But "balance" is never my primary goal because I don't find
the concept helpful, either when deciding what to do next or when
evaluating the results.

I say "balanced" is your primary goal though you do not realize it.
You want to balance the energy propagation in your dipole "lossy
transmission line", when feeding it with an unbalanced coax. The balun
should accomplish that. Anything reflected is not good but at least it
is reflected "unbalanced" inside the grounded shield causing less EMI.

Dan wrote:
On Aug 31, 3:07*pm, Ian White GM3SEK wrote:
Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.
Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. *A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition *of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A common mode choke is used in RF applications, very true, but it
serves a filtering purpose,
not a conversion of unbalanced to balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..


Common-mode chokes, and filters in general, do NOT aim to "turn unwanted
RF into heat"! That is a total misunderstanding of the whole concept.

An ideal common-mode choke would dissipate zero heat energy, and a
successful real-life choke will dissipate only a tiny fraction of the
available RF power.

When you insert a common-mode choke, you are inserting a large impedance
into the pathway of the common-mode current. The RF current
distribution throughout the entire antenna/feedline/ground system will
adjust to take account of this new impedance. As a result, most of the
common-mode current will be DIVERTED away from its former pathway, and
will flow instead in the antenna.

The details are complicated, but the concept that the choke DIVERTS
common-mode current away from the feedline is reasonably accurate. (By
contrast, the concept that it "turns unwanted RF current into heat" is
just plain wrong.)

If the choke is doing its job, the new value of common-mode current
(I_cm) flowing through the choke will be much less than the previous
value. The power dissipation in the choke will then be (I_cm)-squared x
R, where R is the resistive part of the choke's impedance at that
frequency. Note that I_cm is the small amount of common-mode current
that remains *after* having inserted the choke - not the value before!
The practical outcome is that a higher choke impedance will give *lower*
heat dissipation in the choke itself.

If a common-mode choke is getting hot, it isn't working. Unfortunately
there are many chokes that don't have a high enough impedance to handle
the full range of real-life situations. If a choke is not able to
suppress the common-mode current to a low enough value, then in some
situations it will get hot [1, 2]. But PLEASE don't imagine that is
how common-mode chokes are intended to work!

[1] http://www.w8ji.com/Baluns/balun_test.htm

[2] http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

Also see other pages and publications from the same authors.



A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

You do not want the balun to operate hot (ir to dissipate heat as you
do with a CM choke filter). You strive for 100% transfer of energy and
settle for the best
you can get. With a CM choke, you try to filter and dissipate unwanted
back-RF. Any back RF from your balun
should be converted to unbalanced transfer back to the source. You
reduce back-RF by matching impedances (which can also involve baluns
but not the 1:1 application discussed here). If you try to filter it
the unwanted back-RF, you will also end up filtering the forward
energy transfer. Of course, that would be an undersirable situation.


Sorry, but that is so confused I can't even begin to unpick it... except
by pointing to "you try to filter and dissipate unwanted back-RF". In so
many different ways, that is NOT what we're trying to do. Tug on that
loose strand, and the whole thing unravels.



And also, what exactly do you mean by "balanced" in the context of a
feedline?

For a 2 conductor feedline, the V in each conductor is 180 degrees out
of phase with each other. Same with I.

Yes.

One conductor is +90 degrees
and the other is -90 degrees with respect to earth.

No. Earth and 90 degrees don't come into this at all.

At any given
instant and location the summation of both conductors with respect to
each other is equal to the magnitude it would be on the inner
conductor on the unbalanced (coax) with respect to ground (shield).
Since magnitude of the V on each conductor of the balanced line are
equal and opposite in phase, the term "balanced" is appropriate. Same
with I.

Yes... but this definition of "balanced" also REQUIRES that the
common-mode current is zero. The two are locked together, so if
"balance" is your aim, the practical way to achieve it is to force the
common-mode current to a lower value.

We have some direct leverage on common-mode current, because it's a
real, measurable thing. But "balance" is only a concept, and there isn't
any *direct* leverage that we can apply to it.

So even though a "common-mode choke" and a "current balun" are two
different names for the same physical device, it does make a difference
which name you choose. Think "common-mode choke", and you can see the
levers that will make your antenna/feedline system perform the way you
want it to. Think "balun", and all you see is a label that covers those
levers up.


[...]
But think of your dipole as a balanced transmission line. That's what
it is, with a lot of loss (into radiation resistance).
You WANT common mode on THAT that lossy transmission line and you do
not want it filtered away.

Again, that is all so misconceived - at every turn, it clashes with
obvious, measurable physical reality; or else it contradicts itself.
I'm sorry, but you really do need to do a clean wipe and start again
with a good textbook.


--

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

wrote:
A common mode choke is used in RF applications, very true, but it
serves a filtering purpose, not a conversion of unbalanced to
balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..

The common "W2DU balun" works well as both choke and
balun function.
--
73, Cecil http://www.w5dxp.com

wrote in news:c2a78f6b-eded-4547-ae32-bc8ccd60e186
@m73g2000hsh.googlegroups.com:

Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. A CM choke is an EMI prevention

I suggest that a reasonable definition of a balun is any device that
facilitates or assists transition from unbalanced to balanced mode of
operation. That definition permits a wide range of devices that may have
characteristics suited to specific applications.

(Keeping in mind that an unbalanced feedline is often not ideal in
application, ie one where common mode current is exactly half of the
differential current, and a two wire open line is often not ideal in
application, ie where common mode current is zero.)

Most people naturally think of balance in terms of voltages wrt some common
reference, eg ground. It is equally legitimate, and often more appropriate
to the antenna / feedline scenario, to seek balance in terms of current, ie
to minimise common mode current.

Owen

Owen Duffy wrote:

...
I suggest that a reasonable definition of a balun is any device that
facilitates or assists transition from unbalanced to balanced mode of
operation. That definition permits a wide range of devices that may have
characteristics suited to specific applications.
...
Owen

Baluns and Ununs use a transmission line mode to accomplish their tasks
.... anything else is just a RF xfrmr ...

However, there are the 180 degree hybrid baluns ...

Regards,
JS