tech. Q. about balun
 

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I have a rookie question related to baluns.

In what sense is said that

a coax. cable is an unbalance line
an antenna is a balanced system
a twin cable is a balanced line ?

Of course a second question would be how does the balun interface a balanced
and an unbalanced system?

Cordially,

Nic.
http://www.csd.uwo.ca/~nic





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In article ,
"Nicolae Santean" wrote:

I have a rookie question related to baluns.

In what sense is said that a coax cable is an unbalance line

The outer shield is ground and the inner carries the signal
asymmetrically.

an antenna is a balanced system a twin cable is a balanced line ?

If you have a balanced antenna like a dipole then yes.

Of course a second question would be how does the balun interface a
balanced and an unbalanced system?

By shifting the ground reference, splitting and phasing the signal to be
differential going from unbalanced to balanced and performing the
reverse actions to go the other way.

--
Telamon
Ventura, California

NS,

FEEDLINES:

A Coax Cable is an Unbalanced Line (Single Wire and Ground Shield).

Balanced Lines are like Ladder Line and TV type Twin Lead (Dual Wires).

ANTENNAS:

Balance 'type' Antennas: Dipoles, Loops, Rhombic, Inverted "V", etc.

Unbalanced 'type' Antennas: Long Wire, Zep, Random Wire, Inverted "L",
Sloper, etc.

MATCHING TRANSFORMERS / BALUNS / MLBs:
* Balun Reading List ( Long )
http://groups.yahoo.com/group/Shortw...na/message/337

A Matching Transformer can be used to 'connect' an Antenna Element
to a Feed Line.

A "Balun" is specific type of 'matching transformer' that is used
to 'connect' a Balanced Antenna to an Unbalanced Feed-Line.

Another specific type of 'matching transformer' that is used
to 'connect' an Unbalanced Antenna to an Unbalanced Feed-Line
is called a "Magnetic Long Wire Balun" (MLB). The MLB is often
used with the common Random Wire Antennas and Coax Cable
Feed-Lines used by most Shortwave Listeners (SWLs).
* Magnetic Longwire Balun (MLB) - Build Your Own "DIY"
http://groups.yahoo.com/group/Shortw...na/message/177
http://groups.yahoo.com/group/Shortw...na/message/466
http://groups.yahoo.com/group/Shortw...na/message/467


READ these three Links 'presented' by John Doty:
[ Hosted by The Association of North American Radio Clubs "ANARC".]

* Longwire Impedance Matching. {Check-Out the Graphs}
http://www.anarc.org/naswa/badx/ante..._longwire.html
Actually, a fixed Matching Transformer can dramatically reduce the
wild swings in Antenna Efficiency that a Coax Fed Wire Antenna
exhibits.

* Grounding is the KEY to Good Reception
http://www.anarc.org/naswa/badx/antennas/grounding.html

* Low Noise Antenna Connection
http://www.anarc.org/naswa/badx/ante...e_antenna.html


iane ~ RHF
..
Some Say: On A Clear Day You Can See Forever.
http://groups.yahoo.com/group/SWL-AM...na/message/502
I BELIEVE: On A Clear Night...
You Can Hear Forever and Beyond, The Beyond !
..
..
= = = "Nicolae Santean" wrote in message
= = = ...
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I have a rookie question related to baluns.

In what sense is said that

a coax. cable is an unbalance line
an antenna is a balanced system
a twin cable is a balanced line ?

Of course a second question would be how does the balun interface a balanced
and an unbalanced system?

Cordially,

Nic.
http://www.csd.uwo.ca/~nic

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..

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Okay, I think we should take it slowly (probably I have less knowledge than
you think).

Assume we talk about a receiver's antenna.

A dipole antenna is said to be a "balanced" system. To what apply the
qualifier "balanced"? What is "balanced" in the dipole? RF current
distribution (should be along this line)?

Then, about the feed lines. If an arbitrary cable is impedance-matched to
the antenna and is not grounded, it seems that the current distribution
mimics that of the antenna. Is grounding which makes a difference ? What can
be "unbalanced" in a feed line?

I am interested in understanding the concept, really. Intuitively, when
something is qualified as "unbalanced", it refers to some sort of asymmetry
in characteristics. What specifically are these characteristics and
why/where are they asymmetric?

So really, the question stands up. Please be more elementary in explanation.
Thanks a lot.

Cordially,

Nic.
http://www.csd.uwo.ca/~nic

"Nicolae Santean" wrote in message
...

In what sense is said that

a coax. cable is an unbalance line
an antenna is a balanced system
a twin cable is a balanced line ?

Of course a second question would be how does the balun interface a
balanced
and an unbalanced system?




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Nicolae Santean wrote:

So really, the question stands up. Please be more elementary in explanation.
Thanks a lot.

An electrical generator is most efficient when the load impedance(1)
is the same as the generator impedance. That is when it can deliver
the most power.

In a receiver setup, the antenna is the generator(2) and the leadin
cable + radio is the load. When the two impedances are matched, as
above, the maximum amount of energy can be transfered from the
antenna to the radio.

The leadin coax + radio has a set impedance, as does the antenna(3).
The 'balun' or 'unun' is the means used to match these two items via
a ratio of windings.

Sometimes the balun is used directly between a tuner circuit and
antenna..usually in a transmitter setup. The rules for receiving and
transmitting antennas are very very similar but as a rough rule of
thumb, receiving antennas are more forgiving of design errors.

Lots of good sites out there. a quick search will get you some more
results.

http://www.qsl.net/aa5tb/balun.html
http://home.att.net/~DickWD8CEB/Balun.html


(1) Impedance is opposition to current flow, not necessarily of the
resistive kind only.
(2) A wire being crossed by radio waves generates a small electrical
signal.
(3) A normal, fixed length of wire as opposed to the multi tapped
varieties used by those with large antenna farms..


mike




mike

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Thank you for the detailed answer. Below are my comments.

An electrical generator is most efficient when the load impedance(1)
is the same as the generator impedance. That is when it can deliver
the most power.
......
However, I was not talking about impedance matching - which is the job of a
transmatch(tuner) - but rather about coupling a balanced and an unbalanced
segment. Some people - like myself till recently - confuse the impedance
matching with the balun coupling. I agree that a balun can sometime do both,
but its main purpose is to couple balanced and unbalanced segments.

The leadin coax + radio has a set impedance, as does the antenna(3).
The 'balun' or 'unun' is the means used to match these two items via
a ratio of windings.

Nope. There are baluns (1:1) which are not designed for impedance matching.

So, I made some research and I got at least a partial understanding :

In a dipole, the electrical potential swings symmetrically above(+) and
below(-) the "ground level"( 0 ) - that's why is called a "balanced" system.
Both poles of a dipole are "hot", in the sense that they generate/receive
useful RF signal - of course out of phase.

By contrary, a coax has the shield set to 0 potential (grounded) and only
the inner wire is "hot" (carries signal). That is why is called an
"unbalanced" line.

If a coax is used to feed the antenna then the coax has only one "hot" wire
(the inner one). The outer shield is "grounded", hence is "set to 0". If a
balun is not used to couple the antenna with the coax, then one pole becomes
RF inert, since is grounded by the coax. In this case, the dipole antenna
becomes a poor inverted L antenna, since only one pole acts as an antenna.
In case that the coax is not grounded, then it is equally bad : the feed
line becomes part of the antenna and it degrades its performance.

The purpose of a balun is to change the phase of the currents delivered by
the dipole such that it creates an additive effect and feed the inner wire
of the coax with added signal from both poles. So basically, the balun
"collects" the signal from both poles, adds them up and pump them through
the inner wire of the coax. It does so through a transformer coupler. For
example, if the dipole is polarized (+x volts, -x volts) , then the balun
feeds the coax with (0 volts, +2x volts). As a side effect, the balun
isolates the antenna and the line such that the line does not influence the
operation of the antenna.

Please keep me honest - tell me whether I got it right.

Yours cordially,

Nic.
http://www.csd.uwo.ca/~nic





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This was a good explanation actually. It just took me time to understand it.

Thanks, Nic.


By shifting the ground reference, splitting and phasing the signal to be
differential going from unbalanced to balanced and performing the
reverse actions to go the other way.

--
Telamon
Ventura, California




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NS,

"Please keep me honest - tell me whether I got it right."

Yes - You Got it Right. For a Dipole (Balanced) and a Coax
Cable (unbalanced) set-up with a Matching Transformer (Balun)
between them.

Your basic description of a Coax Cable would also apply to a Single
Wire Antenna like a Longwire or Random Wire which is an Unbalance
Antenna. So then the Matching Transformer becomes a "Un-Un".

Keep-Oon Your Quest for Knowledge ~ RHF
..
..
= = = "Nicolae Santean" wrote in message
= = = ...
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Thank you for the detailed answer. Below are my comments.

An electrical generator is most efficient when the load impedance(1)
is the same as the generator impedance. That is when it can deliver
the most power.
......
However, I was not talking about impedance matching - which is the job of a
transmatch(tuner) - but rather about coupling a balanced and an unbalanced
segment. Some people - like myself till recently - confuse the impedance
matching with the balun coupling. I agree that a balun can sometime do both,
but its main purpose is to couple balanced and unbalanced segments.

The leadin coax + radio has a set impedance, as does the antenna(3).
The 'balun' or 'unun' is the means used to match these two items via
a ratio of windings.

Nope. There are baluns (1:1) which are not designed for impedance matching.

So, I made some research and I got at least a partial understanding :

In a dipole, the electrical potential swings symmetrically above(+) and
below(-) the "ground level"( 0 ) - that's why is called a "balanced" system.
Both poles of a dipole are "hot", in the sense that they generate/receive
useful RF signal - of course out of phase.

By contrary, a coax has the shield set to 0 potential (grounded) and only
the inner wire is "hot" (carries signal). That is why is called an
"unbalanced" line.

If a coax is used to feed the antenna then the coax has only one "hot" wire
(the inner one). The outer shield is "grounded", hence is "set to 0". If a
balun is not used to couple the antenna with the coax, then one pole becomes
RF inert, since is grounded by the coax. In this case, the dipole antenna
becomes a poor inverted L antenna, since only one pole acts as an antenna.
In case that the coax is not grounded, then it is equally bad : the feed
line becomes part of the antenna and it degrades its performance.

The purpose of a balun is to change the phase of the currents delivered by
the dipole such that it creates an additive effect and feed the inner wire
of the coax with added signal from both poles. So basically, the balun
"collects" the signal from both poles, adds them up and pump them through
the inner wire of the coax. It does so through a transformer coupler. For
example, if the dipole is polarized (+x volts, -x volts) , then the balun
feeds the coax with (0 volts, +2x volts). As a side effect, the balun
isolates the antenna and the line such that the line does not influence the
operation of the antenna.

Please keep me honest - tell me whether I got it right.

Yours cordially,

Nic.
http://www.csd.uwo.ca/~nic





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http://www.newsfeed.com - The #1 Newsgroup Service in the World!
-----== 100,000 Groups! - 19 Servers! - Unlimited Download! =-----

In article ,
"Nicolae Santean" wrote:

*** post for FREE via your newsreader at post.newsfeed.com ***

Thank you for the detailed answer. Below are my comments.

An electrical generator is most efficient when the load impedance(1)
is the same as the generator impedance. That is when it can deliver
the most power.
......
However, I was not talking about impedance matching - which is the job of a
transmatch(tuner) - but rather about coupling a balanced and an unbalanced
segment. Some people - like myself till recently - confuse the impedance
matching with the balun coupling. I agree that a balun can sometime do both,
but its main purpose is to couple balanced and unbalanced segments.

The leadin coax + radio has a set impedance, as does the antenna(3).
The 'balun' or 'unun' is the means used to match these two items via
a ratio of windings.

Nope. There are baluns (1:1) which are not designed for impedance matching.

So, I made some research and I got at least a partial understanding :

In a dipole, the electrical potential swings symmetrically above(+) and
below(-) the "ground level"( 0 ) - that's why is called a "balanced" system.
Both poles of a dipole are "hot", in the sense that they generate/receive
useful RF signal - of course out of phase.

By contrary, a coax has the shield set to 0 potential (grounded) and only
the inner wire is "hot" (carries signal). That is why is called an
"unbalanced" line.

If a coax is used to feed the antenna then the coax has only one "hot" wire
(the inner one). The outer shield is "grounded", hence is "set to 0". If a
balun is not used to couple the antenna with the coax, then one pole becomes
RF inert, since is grounded by the coax. In this case, the dipole antenna
becomes a poor inverted L antenna, since only one pole acts as an antenna.
In case that the coax is not grounded, then it is equally bad : the feed
line becomes part of the antenna and it degrades its performance.

The purpose of a balun is to change the phase of the currents delivered by
the dipole such that it creates an additive effect and feed the inner wire
of the coax with added signal from both poles. So basically, the balun
"collects" the signal from both poles, adds them up and pump them through
the inner wire of the coax. It does so through a transformer coupler. For
example, if the dipole is polarized (+x volts, -x volts) , then the balun
feeds the coax with (0 volts, +2x volts). As a side effect, the balun
isolates the antenna and the line such that the line does not influence the
operation of the antenna.

Please keep me honest - tell me whether I got it right.

Yes I would say you got it right.

--
Telamon
Ventura, California