UDXF discussion on baluns

[Fansome]

From:         udxf@yahoogroups.com on behalf of bri9hu  (mvarnhem@planet.nl)
Sent:    Thu 7/01/10 4:54 PM
To:    UDXF@yahoogroups.com

Excellent practical info about baluns on:
 
http://home.comcast.net/~markwa1ion/exaol2/z_transformers.pdf
 
http://www.dxing.info/equipment/impedance_transformer_bryant2.doc
 
http://www.dxing.info/equipment/impedance_matching_bryant.pdf
 
 
 
Max
The Netherlands
 From:         udxf@yahoogroups.com on behalf of n0sya  (n0sya@yahoo.com)
Sent:    Mon 6/28/10 9:30 AM
To:    UDXF@yahoogroups.com

Hi Rowland, the multipliers realting to baluns are the values that one would select to multiply the impedance of the antenna or transmissions line, wether coax, single wire, or twin lead. These values are fixed by the turns ratio of the wires on the balun as well as the core material. Baluns are typically made on certain ferrite or powdered iron cores with specific turns ratios, various mixes of cores and turns windings nets you the different multiplier values, just as in any other transformer of the electrical variety.
 
 Antennas transfer most energy when matched to a transmission line with their native impedance, a dipole cut for any specific frequency usualy exhibits an impedance of 75ohms at that frequency, so the naked dipole is a fair match to 50 ohm coax or better yet, 75ohm coax, but then since one is going from a balanced circuit (the dipole) to an unbalanced circuit (the coax), one may still want a balun, but in this case a 1 to 1 ratio is best as you may have guessed. Now if your antenna is a long wire (wich is also an unbalanced antenna), wich may have an impedance at the frequency of interest of 300 to 2000ohms or so, one would use a balun transformer of the required multiplier value to get best energy transfer from the high impedance antenna to the low impedance transmission line, and vice versa.
 
It's all about getting the most energy to and from the load.
 
With a folded dipole (really a loop antenna) like the T2FD antenna around 600ohms impedance nominaly, you would use a 4 or 6 to 1 balun as the matching transformer to get best energy transfer to the coax lead in.
 
There are two reasons one wants a balun transformer, to match the load (antenna) impedance to the line (coax or twin lead or single wire) impedance so as to get maximum energy transfer, and to go between what is called a balanced line, like twin lead or a dipole antenna where there are always two conductors, to an unbalanced condition such as with coax cable and uhf sockets on the back of radios where you have one conductor surrounded by a "ground".
 
Most folks employ baluns (meaning balanced to unbalanced transformer) simply to get maximum energy transfer, but they are very usefull for keeping unwanted rf currents from flowing where one does not want them such as on the outside of the coax lead. One can effect suitable balun action of the keep-rf-off-my-coax variety by merely slipping come ferrite or powdered iron cores onto the coax line near the ends, the cores, if of correct material for the frequency range, will do a fine job of reducing rf flowing on the outer sheild of the coax.
Just some thoughts for you.
 
Baluns:
http://www.radioworks.com/nbalun.html
http://en.wikipedia.org/wiki/Balun
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=3767
 
 
T2FD info
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fd.html
http://en.wikipedia.org/wiki/T2FD_Antenna
http://www.wellbrook.uk.com/UMBT2FD.html
 
Antennas in general:
http://www.hamuniverse.com/n4jaantennabook.html
 
 
 
Chris
 
 
 > To: UDXF@yahoogroups.com
> From: jim@sideband.bbmax.co.uk
> Date: Mon, 28 Jun 2010 16:12:21 +0000
> Subject: Re: [UDXF] Re: BALUN
>
> At 13:28 28/06/10, Chris wrote:
>
<previous email snipped>

> Whatever the turns ratio/impedance ratio, a long wire balun will seldom match
> properly to a coax feedline. The long wire balun, although a compromise at
> matching impedances, does provide a screened feedline to the receiver which will
> not usually pick up noise, particularly if the screen is earthed/grounded near the
> antenna feedpoint. Thus the antenna can (hopefully) be positioned well away from
> the domestic noise environment, avoiding the rubbish usually induced into a
> single-wire feedline from TVs, monitors, PSUs etc.
>
> --
> 73 de Jim,
> (MPJ)
 

[SW-J]

Baluns are typically made on certain ferrite or powdered iron cores with specific turns ratios, various mixes of cores and turns windings nets you the different multiplier values, just as in any other transformer of the electrical variety.

Bzzzzt!

The 'core mix' has very little to do with 'multiplier values' but has to do with increasing the magnetic field flux density and therefore the inductance value and the effective coupling seen between primary and secondary windings ... higher core permeabilities mean fewer turns are required to obtain a particular flux value, but the ratios between a pri winding and sec winding would remain the same - no change in ratio there.

Just thought I would clear up what may be a misconception ...

[cmradio]

Yes, but ferrite will "flux out" and permeability fall to zero with oversaturation (usually caused by too small core or DC in the lines somehow causing trouble) far quicker.

Iron powder is less susceptible to ID-10-T errors

I did a test with a 1/2" "T" and "FT" toroid, identical windings and a 12W CB... the "FT" heated up a heckuva lot quicker with a 2:1 mismatch.

Thanks for the linkage, Al!

Peace!

[SW-J]

Yes, but ferrite will "flux out" and permeability fall to zero with oversaturation (usually caused by too small core or DC in the lines somehow causing trouble) far quicker.

Iron powder is less susceptible to ID-10-T errors

I did a test with a 1/2" "T" and "FT" toroid, identical windings and a 12W CB... the "FT" heated up a heckuva lot quicker with a 2:1 mismatch.

Thanks for the linkage, Al!

Peace!

Selection of proper materials for usually the _lowest_ frequency of operation is part of the design process ... the core manufacturers have in their datasheets/catalogs formulas for calculating magnetic flux densities and the maximums for the various ferrite and powdered iron materials ... so, *do the math, select the proper material and all should be well!

(*Been there - done that)

[cmradio]

... so, *do the math, select the proper material and all should be well!

(*Been there - done that)

Agreed!

Peace!

[Tube Shortwave]

And let's not forget about the difference between voltage baluns and current baluns.

A current baluns is used for a true balanced antenna, like a dipole.  A voltage balun is ideal for end fed antennas, like an inverted L or a bev.

[cmradio]

Voltage baluns + dipole are also great for very assymetric mounting of said dipole

Peace!

[SW-J]

Posted for reference:

   CURRENT AND VOLTAGE BALUNS - DEFINITION

[Tube Shortwave]

That 'reference' was more like an opinion than a fact.

A voltage balun is designed to be connected to the dipole at the voltage node where high breakdown insulation is required and smaller conductors may be used.  A current balun is designed to be connected to a dipole at a current node where lots of insulation is unnecessary but larger diameter conductors are a must.

People (mostly hams) really confuse the two, and some believe there is no difference.  Usually the same kind of 'expert' that calls Heliax 'hardline'.  Everyone who knows anything about radio knows that hardline comes in sections and bolts together.  Heliax is semi-flexible coaxial cable, usually with a jacketed corrugated solid shield.  Hardline has no corrugations and connects using flanges for the outer and 'bullets' for the inner conductors.

73, TS

[SW-J]

That 'reference' was more like an opinion than a fact.

A voltage balun is designed to be connected to the dipole at the voltage node where high breakdown insulation is required and smaller conductors may be used.  A current balun is designed to be connected to a dipole at a current node where lots of insulation is unnecessary but larger diameter conductors are a must.

People (mostly hams) really confuse the two, and some believe there is no difference.  Usually the same kind of 'expert' that calls Heliax 'hardline'.  Everyone who knows anything about radio knows that hardline comes in sections and bolts together.  Heliax is semi-flexible coaxial cable, usually with a jacketed corrugated solid shield.  Hardline has no corrugations and connects using flanges for the outer and 'bullets' for the inner conductors.

73, TS

We are going to have to agree to disagree on some of this ... I don't have time to wage a full-scale war on this, nor would if be worth my time (there isn't enough time to right all the wrongs, the wrong headedness and stubbornness in this world).

Let's just say EVERYONE has their fair share of misconceptions on this subject.

And - if push comes to shove, I'm the guy who invented the 6M Heliax duplexer when the 'consensus' said it couldn't be done ...

[Tube Shortwave]

No war needed, or requested.

For the record, I'm the guy who builds commercial AM, FM, TV, and SW antennas.  I build baluns to handle 500 KW continuous duty.  I know a thing or two about baluns too.

73.

[SW-J]

No war needed, or requested.

For the record, I'm the guy who builds commercial AM, FM, TV, and SW antennas.  I build baluns to handle 500 KW continuous duty.  I know a thing or two about baluns too.

73.

Anything original? (Anything I can't find in Jasik?)

Building onesey - twosey units with significant overdesign that a particular market will bear (cost-wise) is a relatively easy thing to do (it's physics: the physics will dictate the size the spacing, the selection of materials, etc etc) ... and while 500KW is not insignificant, is pales in comparison to some RADAR peak powers (which I've had experience with too while with a defense contractor). Could go on ... won't.

See, no wants 'war' but it always results ... to a point.

BTW, this 'current' or 'voltage' balun (here I am falling into your world) thing would appear to be a recent 'internet' thing; you still can't perform the function you desire (eliminate common mode currents) without involving both currents and voltages (creating electric and magnetic fields) as expressed using Maxwell's equations ... and when you *do* succeed with a particular balun design, it is effective only to a particular value (call it CMRR if you will), maybe 20, 25 dB ... perhaps 30 with careful attention and tuning on onesey - twosey designs.

A side question, in which category would place a "Robert's Balun"? Voltage or Current?

[Tube Shortwave]

I see we do agree on most points. 

Choice of materials dictates the E or I characteristics.

A Roberts balun (no apostrophe) is a fairly recent design by Bill Roberts that is a modified 1/4 wave current choke.  With a 70 ohm load on output, one would see a 50 ohms load on input.  Neat way to match a dipole.  It would most certainly be built as a current balun.