eHam.net - Amateur Radio (Ham Radio) Community

Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net



[Articles Home]  [Add Article]  

How a 1:4 Guanella-Balun (Current-Balun) Operates

from Jerry Sodus, KM3K on August 30, 2010
View comments about this article!

How a 1:4 Guanella-Balun (Current-Balun) Operates


ByJerry Sodus, KM3K

1. The purpose of this article is to show how a 1:4 Guanella (current)-balun changes an impedance level by a multiplier of four; for example, 50-ohm coax to a 200-ohm antenna.
Although this is not a “how to make the balun” article, some design information is given for completeness.

2. Also, just to let you know…the Guanella (current)-balun can be turned around to go the other way; for example, a 50-ohm coax can be changed down to 12.5-ohm (say for a Yagi-antenna or a vertical-antenna).
We’ll cover this later in paragraph #12.

3. BTW, Guanella came up with this idea in 1944.
In 1985, Roy W7EL gave Guanella’s idea the name “current-balun” because the balun’s output supplies equal current into/out of the output pins and that is a good thing.

4. It is important to put out of your mind any idea about flux-linkages and conventional-transformer action.
Those concepts have nothing to do with this article.

5. The 1:4 Guanella (current)-balun is made from two 1:1 Guanella (current)-baluns.
Except for winding direction, they should be as identical in construction as possible to minimize any variation in signal delays; variations will increase signal loss at the higher frequencies.

6a. The 1:1 Guanella (current)-balun can be made up in several different ways:
A) coiling coax,
B) winding a transmission-line (coax or two-wire) on a toroid-core or rod; ferrite core/rod preferred,
C) threading coax thru ferrite-beads.

6b. Figure 1 has the usual schematic used for a 1:1 current-balun.

6c. To emphasize that the transmission-line mode is working here, lets use the schematic as in Figure 2.

6d. Here is a key point.
We’ll assume that any signal loss thru the balun will be small enough that we can ignore it.
So, whatever voltage is at the input of the 1:1 balun is what we’ll see at its output.
In other words, we assume the signal’s voltage-level is not attenuated by the 1:1 balun.
In practice, we can approach this goal by using high-quality transmission-line and keeping its length short.

7. You connect up the baluns in this way as shown in Figure 3 below.

7a. The inputs are in parallel.
That means that any current going into terminal P3 splits in two, half goes up to terminal 3 and the other half will go down to the other terminal 3.
At terminal P1, the currents coming out of each terminal 1 combine at P1 to flow back to where it started.
Although P1 and P3 are where we will eventually the feed-line from the transmitter when we use the balun, for us right now, the feed-line is not connected.

7b. The outputs are in series.

Notice that if we were to connect an ohmmeter to P1 and P3 at this time, we’d read a short-circuit.

7c. Next connect a load ‘RL’, which we assume is a just a resistor for our purposes at this time. See Figure 4.
You may recall that a resonant-antenna is just a resistor, in other words, a pure resistance (no reactance).

It’s interesting that, in Figure 4, the current going around the “inside-loop” never gets to the load RL.
The “inside-loop” is from P3 going down to balun-A’s terminal 3, then to terminal 4, up to balun-B’s terminal 2, over to terminal 1 and then to terminal P1.

8. There is a term “input impedance” and we’ll use the symbol “Zin” for it.
In case “input impedance” is a new idea for some, here is a short explanation...
For us electronic folks, it is the value of impedance we’d measure at a test-frequency if we could connect up a special kind of alternating-current ohmmeter to terminals P1 and P3 in Figure 4.
That value of Zin would replace the entire circuit to the right of P1 and P3.
For us right now, we are only concerned with the idea of “input impedance” and not with any actual value.

9. We’ll use the schematic in Figure 5 to find the power going into Zin.
A key point here is to remember this is really the power going into the input of the 1:4 balun (at P1 & P3).
In Figure 5, we are not concerned with the transmitter or its output-resistance.
All we really care about is that there is Zin and a voltage across it; we’ll call that voltage “V”.

Recall that power going into a resistor is equal to ‘the voltage across the resistor’ times ‘the voltage across the resistor’ divided by ‘that resistance’.
So using our symbols, we can write the “power into the 1:4 balun” equals “V times V divided by Zin”.

10. Next we need the power going into the load RL.
So, we need to know the voltage across RL.
Here is how we’ll figure out what its value is.

10a. Recall that the voltage across P1 and P3 is V.
This is the same voltage across pins 1 and 3 at each of the 1:1 baluns.

10b. In step 6d, it is written that the same voltage V will be at each output of the 1:1 baluns.

10c. Step 7b has the outputs of the 1:1 baluns connected in series.
So this means V plus V equals 2V is across the load RL.
(If you have trouble understanding this, perhaps this may help.
Just for now, pretend that each 1:1 balun output is a battery.
So we have two batteries connected in series; just like in a flashlight and the light-bulb is the load.
If each battery is 1.5 volts, we’d have 1.5 volts plus 1.5 volts equals 3 volts across the load.)

10d. The “power going into RL” is “2V times 2V divided by RL”.

11a. Now we are at the KEY section; the reason for this article.
We are assuming there is no power lost in the baluns and that is a reasonable approximation throughout most of the 1:4 balun’s passband.
We can write…”POWER INTO THE 1:4 BALUN” equals “POWER GOING INTO RL”.
Paragraph 9 gives the “power into the 1:4 balun”.
Paragraph 10d gives us the “power going into RL”, so we can write here…
“V times V divided by Zin” equals “2V times 2V divided by RL”.
Doing all the algebra, we come up with …..”RL equals 4 times Zin”.
So we have proved we have a 1:4 impedance-ratio.

11b. An example ……….if Zin is 50-ohms, then RL is 200-ohms.
11c. Another example…..if Zin is 75-ohms, then RL is 300-ohms.

12 If we turn the 1:4 balun around to get a 4:1 balun, we can step-down in impedance.
For example, 50-ohms divided by 4 equals 12.5-ohms (maybe for a Yagi antenna); see Figure 6.

13. Comments about the transmission-line used in a 1:1 Guanella (current)-balun:

13a. The value of its characteristic-impedance Z0 (that is Z and a zero; pronounced Zee naught) is important.

13b. The 1:4 balun has a low impedance side and a high impedance side.
Whatever the high impedance side is, divided that value by two and that is the characteristic impedance to use in the 1:1 Guanella (current)-balun.

13c. Here are examples of some values for 1:4 Guanella-baluns…
for 50-ohm to 200-ohm, Z0 is 100-ohm.
for 75-ohm to 300-ohm, Z0 is 150-ohm.
for 50-ohm to 12.5-ohm, Z0 is 25-ohm.

13d. You can make your own transmission-line (two-wire or coax); see Sevick’s “Transmission-Line-Transformers”.

13e. The more you deviate from the design Z0, the more power you lose at higher frequencies.

14a. The 1:4 concept can be extended to other ratios like 1:9 and 1:16 and 1:25.
14b. But more 1:1 baluns are needed; the 1:9 uses three; the 1:16 uses four, etc.
14c. The Z0 formula changes also; for 1:9, divide the high impedance by three; divide by four for the 1:16.

15. (Amended 3 Sept 2010) Although Sevick W2FMI (SK) published the concept of a 1:4 Guanella-balun on just one core (in other words, two 1:1 baluns on one core) and stated it should not be used if the load is grounded (virtually or actually) at its center point, W8JI takes great issue with using that concept for even a floating-load because common-mode-impedance can have deleterious effects on performance; for interesting information, please refer to his site at http://www.w8ji.com/balun_single_core_41_analysis.htm.

I hope this article is of some benefit in explaining how the 1:4 Guanella (current)-balun “does its thing”.

73 Jerry Sodus, KM3K; FN10je; member of the South-Mountain-Radio-Amateurs Club

Member Comments:
This article has expired. No more comments may be added.
 
How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on August 30, 2010 Mail this to a friend!
I've sent an email to the ArticleManager about a Figure 6 problem in that a Figure 5 is repeated instead of Figure 6.
Some glitch must have happened to corrupt the material along the way because I have verified that the file I submitted has the correct material.
The old cliche continues on in spite of everybody's best efforts..."Murphy rules".
73 Jerry Sodus KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by N2LK on August 30, 2010 Mail this to a friend!
Very nice info, thanks.
I have built this balun a few times feeding twinlead to my attic dipole (52 ft. flat top) with fairly good results. My rigs internal tuner will tune this setup on 10-40 meters, though I do notice some SWR rise during longer transmissions at higher power (75-100 watts).

One thing you mention caught my eye:
"Except for winding direction, they should be as identical in construction as possible to minimize any variation in signal delays; variations will increase signal loss at the higher frequencies".

I see with mine I wound each 1:1 toroid by winding in a counter clockwise direction. Should I have wound one of them in a Clockwise direction?

Thanks & 73!
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by AC5UP on August 30, 2010 Mail this to a friend!
Note to N2LK:

The winding direction isn't as critical in a two core Balun as the goal of preserving circuit balance by keeping both sides as equal as possible... But... In practical terms the cores will usually be packaged close together and winding them in opposite directions can reduce the level of crosstalk between them.

It has been a few years since I've rolled one, but if I recall correctly winding in opposite directions also has the secondary benefit of arranging the wire leads more conveniently. (?)

I've had poor luck with two windings on one core but have read that winding in opposite directions is required for a mono-core 1:4 Guanella. Considering that I have spare cores in the junque box I'll stick with the two-core style since I know they work and work well.
 
How a 1:4 Guanella-Balun (Current-Balun) Operates  
by WB6MMV on August 30, 2010 Mail this to a friend!
Nice discussion Jerry: I especially like the "battery in series" analogy. Very clear and understandable. Thanks for your efforts
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on August 30, 2010 Mail this to a friend!
To N2LK and AC5UP about winding-direction,
Winding one balun CW and the other CCW makes connecting them together much easier to avoid excessive lead-lengths and so minimize parasitics.
Also, a minimum distance of at least 0.25" between the wound-cores will help reduce coupling between the 1:1 baluns.
73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by N2LK on August 30, 2010 Mail this to a friend!
I never thought to use any separation between the 2 cores. I will rebuild mine now with a separator and see how it works.

I like the convenience of using the rigs tuner via this balun, instant band hoping. But have experienced
some thermal issues, especially on modes like rtty and psk..hence I use my simple balanced tuners instead...

But lets see...
Thanks
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on August 31, 2010 Mail this to a friend!
John N2LK,
Thermal-problem....oh my, that shouldn't be; seems like a re-design is needed.
Although off topic, I am curious.
Could you email me off-line at jsodus@embarqmail.com with answers to these questions?
a) the core in use (especially the permeability),
b) the transmitter's power-level,
c) is the wire-size at least #18?
d) impedance-levels and the Z0?
e) frequency-bands where you experience heat.
73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by AA4PB on August 31, 2010 Mail this to a friend!
Any time you have "thermal issues" it means the balun is disipating RF energy as heat instead of passing it to the antenna to be radiated.
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KE5FRF on August 31, 2010 Mail this to a friend!
Hi Jerry,

I understand the concept here, and the math. The schematics help the student visualize the impedance transformation quite marvelously. Great article.

I wonder, because I take visual cues best, and I assume others do as well, can we see an appendix to this article that shows the currents, voltages, and their phase relationships as they pass through the coils of the baluns? This is the final cream on the cake for the non-engineer type. Or perhaps you can point to a java applet that illustrates the aformentioned? I will consult my trusted friend Google in the mean time. :)

 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on August 31, 2010 Mail this to a friend!
To KE5RFR,

I don’t know of any sites treating the material you’d like to see.
If you come across any, please let us all know.

Here is my attempt for the requested appendix but in words (no graphs):
1. Assume that we have connected together two perfect 1:1 current-baluns that use 100-ohm transmission-line to make a 1:4 current-balun that'll transform 50-ohm to 200-ohms.
2. We connect a perfect 200-ohm load to that 1:4 balun.
3. The mid-point of the 200-ohm load is at the same voltage as the junction of pins 2 and 4 that are tied together.
That means we have 100-ohm across each 1:1 balun output.
Under those conditions, each 100-ohm transmission-line is perfectly terminated with a 100-ohm resistance.
4. A wave starts down each 100-ohm transmission-line.
Because the transmission-line is a pure resistance (no reactance), the voltage and current are in step with each other.
In other words, they are in phase.
In other words, as the voltage changes, at the same time the current changes in the same manner per Ohm's Law.
5. Each wave travels down the transmission-line in a predictable manner using Heaviside's transmission-line equations.
6. The waves in each transmission-line get to the end of the respective line at the same time because the 1:1 baluns are identical.
7. Since each line is perfectly terminated, there are no reflections.
8. All power is used up in the load.

73 Jerry KM3K
 
How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on August 31, 2010 Mail this to a friend!
Mostly correct, but this isn't.

"13c. Here are examples of some values for 1:4 Guanella-baluns…
for 50-ohm to 200-ohm, Z0 is 100-ohm.
for 75-ohm to 300-ohm, Z0 is 150-ohm.
for 50-ohm to 12.5-ohm, Z0 is 25-ohm.

13d. You can make your own transmission-line (two-wire or coax); see Sevick’s “Transmission-Line-Transformers”.

13e. The more you deviate from the design Z0, the more power you lose at higher frequencies."

In order for Z0 to matter, in the TEM mode, one must use a relatively long transmission line. For eample, a 2:1 transformation point is roughly 1/4 wavelength of a transmission line with a Z0 which is the geometric mean of the two.. For example, to transform 100 ohms to 50 ohms, 1/4 wavelength of line with a 75 ohm Z0 is used. At 7 MHz, that's about 25 feet long. 25 feet of bifilar transmission line as two 12 AWG wires wrapped about a core? Good luck.

Cores function as transformers. Conventional broadband current and voltage transformers, not transmission line transformers that are unique lengths for unique frequencies!!!!

Core material and permeabilities are very important. So is self impedance of each winding. Windings should have at least five and preferably ten times the source impedance to minimize winding losses.

Sevick didn't do transmission line transformers. If he did, they would have had hundreds wraps of wire and many taps to achieve the same impedance ratios at different frequencies!!!

 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 1, 2010 Mail this to a friend!
Also, since the Guanella concept is based upon current, your explanation model shouldn't use a voltage example, but one showing current(s).

If you start at P3 assuming current divides equally in the primary of balun 1 and its route through its secondary to RL, then the current through RL must be one half of the total current I. Therefore, the total current through RL is 1/2 I. Assuming no losses if everything is perfectly symmetrical, then Power equals 1/2 I squared RL. Solving for RL, it then becomes 4 times the original RL for equivalence.

A Guanella is a good design. Provided, as in all transformers, that sufficient reactance is present to achieve proper transformer performance.
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 1, 2010 Mail this to a friend!
N2LK:
" .......I do notice some SWR rise during longer transmissions at higher power (75-100 watts).

One thing you mention caught my eye:
"Except for winding direction, they should be as identical in construction as possible to minimize any variation in signal delays; variations will increase signal loss at the higher frequencies".

I see with mine I wound each 1:1 toroid by winding in a counter clockwise direction. Should I have wound one of them in a Clockwise direction?"

Each toroidal transformer should stand alone. I doubt that leakage flux is causing your heating problem with the power you're using. Unless your cores are very small, or are a material that is very lossy at HF.

The winding direction should make no difference since they are separate transformers. But, how they are connected would (opposite sense for proper current flow). As a suggestion, if you have an MFJ-459B analyzer, check what the impedance of your antenna is at the balun. Or, better yet, terminate the Guanella with a 200 ohm carbon resistor and see what the MFJ says the value is at its input at various frequencies. It should be 50 ohms with very little reactance if all is working properly.
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 1, 2010 Mail this to a friend!
N2LK:
" .......I do notice some SWR rise during longer transmissions at higher power (75-100 watts).

One thing you mention caught my eye:
"Except for winding direction, they should be as identical in construction as possible to minimize any variation in signal delays; variations will increase signal loss at the higher frequencies".

I see with mine I wound each 1:1 toroid by winding in a counter clockwise direction. Should I have wound one of them in a Clockwise direction?"

Each toroidal transformer should stand alone. I doubt that leakage flux is causing your heating problem with the power you're using. Unless your cores are very small, or are a material that is very lossy at HF.

The winding direction should make no difference since they are separate transformers. But, how they are connected would (opposite sense for proper current flow). As a suggestion, if you have an MFJ-459B analyzer, check what the impedance of your antenna is at the balun. Or, better yet, terminate the Guanella with a 200 ohm carbon resistor and see what the MFJ says the value is at its input at various frequencies. It should be 50 ohms with very little reactance if all is working properly.
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on September 1, 2010 Mail this to a friend!
To W6EM…

Thanks for replying to the article.

Sevick in his books laments about the misconception that many radio-amateurs have about baluns.
One quote, “By far, most misconceptions regarding Baluns are due to the many radio amateurs who perceive these devices as conventional transformers that transmit the energy from input to output by flux linkages and not as transmission line transformers, which transmit energy by an efficient transmission line mode.“
Another quote, “However, it is apparent from the articles published in the amateur radio journals and discussions on the air and at club meetings that most radio amateurs still perceive these devices as conventional transformers. They don’t look at these devices as Guanella and Ruthroff did---as chokes and transmission lines.”

Now lets take time to treat the salient points of your postings….

1. W6EM: “A Guanella is a good design. Provided, as in all transformers, that sufficient reactance is present to achieve proper transformer performance.“
KM3K: No problem with the first sentence but it makes me wonder why all the other comments were made. :)
As for the second sentence and its “….as in all transformers…”; I designed lots of transformers (conventional) in my day and they worked as designed but I never concerned myself with “sufficient reactance”. For a conventional transformer, it’s all about turns-ratio and where you put the windings.

2. W6EM: “In order for Z0 to matter, in the TEM mode, one must use a relatively long transmission line. For eample, a 2:1 transformation point is roughly 1/4 wavelength of a transmission line with a Z0 which is the geometric mean of the two.. For example, to transform 100 ohms to 50 ohms, 1/4 wavelength of line with a 75 ohm Z0 is used. At 7 MHz, that's about 25 feet long. 25 feet of bifilar transmission line as two 12 AWG wires wrapped about a core? Good luck.”
KM3K: Nowhere in Heaviside’s differential equations and its solutions for a transmission-line is there any limit on how long the line must be before his equations can apply. So, from where I sit, I think it would be helpful for W6EM to review Heaviside’s very significant work.

3. W6EM: “Cores function as transformers.”
KM3K: A core by itself is not a transformer. HI

4. W6EM: “Conventional broadband current and voltage transformers, not transmission line transformers that are unique lengths for unique frequencies!!!!”
KM3K: I don’t know what that means.

5. W6EM: “Windings should have at least five and preferably ten times the source impedance to minimize winding losses.”
KM3K: Actually, the reason is to prevent the undesired and harmful conventional transformer current flow.

6. W6EM: “Sevick didn't do transmission line transformers. If he did, they would have had hundreds wraps of wire and many taps to achieve the same impedance ratios at different frequencies!!!”
KM3K: Sevick really truly did along with a host of other like Guanella, Ruthroff, Reisert W1JR, Maxwell W2DU, McCoy, just to name a few.

7. W6EM: “Also, since the Guanella concept is based upon current, your explanation model shouldn't use a voltage example, but one showing current(s).”
KM3K: Here’s my reason for choosing the power formula that used voltage and resistance; I wanted to emphasize the series connection aspect at the output.
If I chose the power formula that uses current and resistance, I get the same answer but that would not emphasize the series connection aspect.

73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 1, 2010 Mail this to a friend!
KM3K:

"Sevick in his books laments about the misconception that many radio-amateurs have about baluns.
One quote, “By far, most misconceptions regarding Baluns are due to the many radio amateurs who perceive these devices as conventional transformers that transmit the energy from input to output by flux linkages and not as transmission line transformers, which transmit energy by an efficient transmission line mode.“
Another quote, “However, it is apparent from the articles published in the amateur radio journals and discussions on the air and at club meetings that most radio amateurs still perceive these devices as conventional transformers. They don’t look at these devices as Guanella and Ruthroff did---as chokes and transmission lines.”"

Yes, Sevick does "lament" this point, but as others who are far more expert and experienced at transmission line theory will attest, the impedance fluctuates along a transmission line. Take a look at a Smith Chart and stop refencing an old mathematician's equations, unless you go through the motions of calculating lengths of line to make your transformation. You'll quickly see on a Smith Chart that as one progresses along a transmission line from generator to load, it takes a significant length to amount to significant transformation. Try the simple 2:1 exercise using a Z0 of 75 ohms and transform 50 ohms to 100 ohms. You'll see that can't be done in an extremely short wavelength of transmission line. It takes approximately 1/4 wavelength to achieve that transformation. So, if that is the case, the only way 10 feet or less of enamelled copper can effect such a transformation at 7MHz, is via transformer action. And, transformer designers of any consequence know that you must have sufficient self impedance to prevent heavy winding losses when connected as a voltage transformer. Perhaps all of your transformers were current types with no burden, forgiving you that omission.

In fact, the fellow with a Guanella core heating problem may have insufficient self impedance since in the four to one example, the primary windings are in series and act as voltage transformers. He should ensure that he has at least 250-500 ohms of self impedance in each winding to avoid heavy winding losses. I erred in not saying that.

Dr. Sevick had some clever examples in his books. But, frankly, as I said before, if he understood the properties of transmission lines well, he'd know that their Z0 and length determine their transformation properties. And, he would have specifically given lengths for all of the windings in his designs if lengths were involved, not just pictures and verbiage. Perhaps even tables of the surge impedance for paralleled enamelled copper wire or various sizes and separations. It does matter if truly a TEM mode transmission line is involved.

Current transformer 1:1 choke baluns are popular and do work well. In your 1:4 example, however, it is connected as a voltage transformer. Some folks like to use a switchable Guanella form to realize either 50 or 200 ohms from two torodial transformers. While that is convenient, the self impedance should be chosen to optimize both the current transformer 1:1 connection and voltage transformer 1:4 configurations. Paralleling of primaries and secondaries, of course, halves the reactance if mutual coupling is discounted. That helps reduce the self impedance value when used as a CT. Most critical, however, is making sure that when connected as a 1:4 that there's enough impedance to keep winding losses low.


"Now lets take time to treat the salient points of your postings….

1. W6EM: “A Guanella is a good design. Provided, as in all transformers, that sufficient reactance is present to achieve proper transformer performance.“
KM3K: No problem with the first sentence but it makes me wonder why all the other comments were made. :)
As for the second sentence and its “….as in all transformers…”; I designed lots of transformers (conventional) in my day and they worked as designed but I never concerned myself with “sufficient reactance”. For a conventional transformer, it’s all about turns-ratio and where you put the windings."

Then, frankly, someone else did the core and winding design(s)for you and gave you a minimun number of turns to start with. Otherwise, your transformers would probably have made good heaters. :-)


"2. W6EM: “In order for Z0 to matter, in the TEM mode, one must use a relatively long transmission line. For eample, a 2:1 transformation point is roughly 1/4 wavelength of a transmission line with a Z0 which is the geometric mean of the two.. For example, to transform 100 ohms to 50 ohms, 1/4 wavelength of line with a 75 ohm Z0 is used. At 7 MHz, that's about 25 feet long. 25 feet of bifilar transmission line as two 12 AWG wires wrapped about a core? Good luck.”
KM3K: Nowhere in Heaviside’s differential equations and its solutions for a transmission-line is there any limit on how long the line must be before his equations can apply. So, from where I sit, I think it would be helpful for W6EM to review Heaviside’s very significant work."

If you're so schooled on determining varioius impedance points on wire transmission lines, use Heavyside's equations to tell us the length the windings need to be for each band that each of your 1:4 Guanellas will be used on to achieve a 50 to 200 ohm transformation. Tell us how many feet of two-wire balanced line for each winding for 160, 80, 40, 30, 20, etc. to achieve 1:4 transmission line impedance transformations.


"3. W6EM: “Cores function as transformers.”
KM3K: A core by itself is not a transformer. HI"

Yes, a Freudian slip. Cores do form the heart of the RF transformers used in the example. Air could be used to, with a sufficient number of turns.

"4. W6EM: “Conventional broadband current and voltage transformers, not transmission line transformers that are unique lengths for unique frequencies!!!!”
KM3K: I don’t know what that means."

Again, apply your Heavyside equations or more simply, a Smith Chart, and you'll understand that you have to adjust line length to achieve desired transformations using transmission lines as transformers.


"5. W6EM: “Windings should have at least five and preferably ten times the source impedance to minimize winding losses.”
KM3K: Actually, the reason is to prevent the undesired and harmful conventional transformer current flow."

Now, coming from a former transformer designer, I'm simply amazed. Five fold the source/load impedance won't begin to stop proper transformer action. Actually, most designs use about ten fold the source and load impedances as self impedance objectives to reduce losses.


"6. W6EM: “Sevick didn't do transmission line transformers. If he did, they would have had hundreds wraps of wire and many taps to achieve the same impedance ratios at different frequencies!!!”
KM3K: Sevick really truly did along with a host of other like Guanella, Ruthroff, Reisert W1JR, Maxwell W2DU, McCoy, just to name a few."

Really were transformers, plain and simple. Oh, some may profess them incorrectly to be/have been transmission line transformations, but frankly, you don't need a core to achieve true transmission line impedance transformations. Only if you want to add some common mode reactance to help choke out common mode current. You can also wrap unbalanced line in a coil at higher HF frequencies and accomplish the same thing.

"7. W6EM: “Also, since the Guanella concept is based upon current, your explanation model shouldn't use a voltage example, but one showing current(s).”
KM3K: Here’s my reason for choosing the power formula that used voltage and resistance; I wanted to emphasize the series connection aspect at the output.
If I chose the power formula that uses current and resistance, I get the same answer but that would not emphasize the series connection aspect."

Yes, after I thought about it for a while, since it is a voltage balun connection and not a current balun in your example, it does make more sense to explain it in terms of voltage. In its 1:1 connection, it is a current transformer balun, but not in your 1:4 example.

Perhaps all of the confusion false-claiming that transmission line transformations are occurring on cores is based upon the popular use of coax line in construction of choke baluns. Frankly, anyone who claims transmission line action without specifying lengths and detailing desired surge impedance for varioius ratios is spouting voo doo science. At least you did show the mean impedance/surge values to do a proper transmission line transformation. Its just that realizing some of those impedances (and lengths of line) would be difficult for HF designs wrapped up around a core of reasonable size. That's why so many folks like using lengths of high impedance ladder line to tune antennas with.




 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by AA5TB on September 1, 2010 Mail this to a friend!
"For every expert there is an equal and opposite expert."

-Arthur C. Clarke (1917- 2008)

;-)

73,
Steve - AA5TB
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on September 1, 2010 Mail this to a friend!
To W6EM....
Based on your last posting, it is now clear to me what the problem is.
Apologies for being “brutally blunt”; it is that you do not possess a fundamental understanding of transmission-line theory in that you seemingly do not know how to prevent impedance variation if it should occur on a transmission-line.
Hence, I sense a concomitant lack in fundamental understanding of the Smith chart as well.

BTW, speaking about the term “impedance”, it was coined by the “old mathematician”, whom you so derisively dismissed; he also coined the words “inductance and capacitance”.
More than any other single individual, Heaviside shaped our approach to analysis of electrical-circuitry.
Additionally, he was the first to suggest the existence of the ionosphere.
Just maybe some things to think about the next time you key up.

Now back to transmission-line fundamentals.
If a transmission-line is terminated in its characteristic-impedance Z0, there is no reflection.
To plot the normalized load on a generic Smith chart, put your dot right smack dab in the very center of the chart.
No reflection means the impedance along the line does not vary.
That means all your verbiage about line-length is irrelevant and unnecessary

With that in mind, now would be a good time to go back and read my reply to KE5FRF (although I typed it as KE5RFR).
At this point, it should make sense to you.
I see no value in repeating it here except for the very significant line#7, which is
“Since each line is perfectly terminated, there are no reflections.”
W6EM, if there is still a problem, come on back and we’ll work it out some more.

One may say, “Well, what happens if the 50-ohm: 200-ohm balun is terminated by something other than 200-ohms?” According to Walt Maxwell W2DU in his latest book “Reflections III” that came out in May-2010 (my current reading project), the only thing I can write at this time is that problem is handled by proper use of an antenna-tuner.

I recommend the Schaum outline on “Transmission-Lines” written by Robert Chipman.
73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 2, 2010 Mail this to a friend!
Frankly, trying to show someone who has no understanding of transmission lines in their use to achieve impedance (reactance and resistance) transformations is futile.

You clearly have ZERO experience with a Smith Chart, as you'd not have spurted such a ridiculous claim as to the horizontal line's purpose. It is the beginning or the end of a line of normalized admittance or impedance being purely conductive or resistive.

Yes, what ever purely resistive source or load that is being modeled begins at that point. If it is a complex impedance, it is above or below the line.

Let's look at it another way. If transmission line couldn't be used to transform an impedance at one end to be a different impedance as one travelled along it, it would be useless as a means to achieve anything more than being a conduit to supply power from a generator to a load without changing anything. That incorporates your fundamental misunderstanding of the concept. The T Line itself can't do it by itself. Oh, but toss in a core and that "transmission line" becomes primary and secondary windings of a transformer and not a function of its very short length wrapped around a small core.

If your textbook was Schaum's Transmission Lines, I suggest you find a better one with a few examples that demonstrate impedance transformations using the Smith Chart that you can understand. There's an old Ham Radio magazine article of more than a few years ago that offers a decent explanation and a few good examples. Buy an archived copy from CQ and have at it. Then buy some transmission line and do some real world transformations and verify they work with a decent instrument like an MFJ 259B.



 
How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JII on September 3, 2010 Mail this to a friend!
Where is Tom(W8JI) when you need him? I'd love to have him in on this!
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on September 3, 2010 Mail this to a friend!
To W6EM,

It is apparent to me now that it will take someone with more ability than I have to convince you what is happening to a transmission-line that is terminated in its characteristic-impedance.

The facts remain:
a) A transmission-line has a characteristic-impedance Z0.
b) When that line is terminated with an impedance equal to Z0, there is no reflection.
c) Under that condition, the input-impedance of that line is Z0 and the length of the line is irrelevant.
d) When that input-impedance is normalized, the value would be plotted at the very center of a generic Smith-chart.
e) Now, if the line is terminated in an impedance other than Z0, there will be a reflected wave and so the line’s input-impedance now is a function of the line’s length and, depending on the termination, may be frequency dependent as well.
The forward-wave follows Ohm’s Law; the voltage and current are in-phase.
The reflected-wave follows Ohm’s Law; its voltage and current are 180 degrees out-of-phase with each other.
The forward-wave and reflected-wave interact in a complex manner causing impedance variations along the line.

There are a number of companies making high-quality products based on the above principles.

About text-books, my college text was by Potter and Fich; it is a pretty solid book on transmission-lines.
Other books in my library that I’ve used for transmission-line and Smith-chart work are:
J.D.Kraus’ “Electromagnetics”,
Slater’s “Microwave Transmission”,
ARRL’s “Handbook 2007” and the “Antenna Book 21st ed.”,
Maxwell’s “Reflections III” (just started reading this new book),
Chipman’s “Transmission-Lines”.

I have read P.H.Smith’s book (1969) about applications of his Smith-chart.
As for actual Smith-chart experience, I’ve got a bunch of professional experience with it on such HP/Agilent instruments as the 3577a , the 8753-series and the more recent E-series.

Rather than the MFJ-259b, I prefer to continue using my AIM-4170 as I’ve seen reports that it is vastly superior to the MFJ product.

So, with all that, it is my hope that someday you’ll come across someone who can better explain this material to you.
73 this is Jerry KM3K over and out.
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JI on September 3, 2010 Mail this to a friend!
I hate to get into this, but the articles statement that a single core can be used in a 4:1 current balun to balance the load if the load floats is absolutely WRONG.

I don't know why that misunderstanding persists, and how we manage to repeat that error in articles, but it is an error.

It is explained here at this link:

http://www.w8ji.com/balun_single_core_41_analysis.htm

If you have a single core 4:1 current balun, you are kidding yourself if you think the load currents are balanced. The only way load current would be balanced is if the load requires a 3:1 voltage split. Very few loads would require that.

I've made extensive measurements of a single core balun on a real antenna and the balance is terrible. It is not a balun at all. It is an impedance transformer that is nether balanced nor unbalanced.

73 Tom

 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JI on September 3, 2010 Mail this to a friend!
As for reversing the 4:1 balun so it transforms 50 ohms down to 12.5 ohms, you would never have a 4:1 ratio except perhaps on the very lowest frequencies.

In order to reverse the balun and have any bandwidth, the transmission lines would have to be 25 ohms. That is a nearly impossible task with balanced lines, so it would have to use coaxial lines.

If the transmission lines are **very short** in wavelengths or 1/2 wave long, the balun could be reversed and it would have close to 4:1 ratio.

Anything will "work", if the definition of "work" is loose enough. The 4:1 50 to 200 ohm balun would "work" if turned around, the only problem is it would not be a 1:4 ratio on any frequency where the transmission lines have any length except near zero or a multiple of 1/2 wave.

As a matter of fact where the lines are 1/4 wave long, often the case up near the upper frequency limit, the 1:4 "backward" balun would be a 50 ohm to 100 ohm balun, not 50 to 12.5 ohms!!! This is because the two transmission lines would become Q sections of 100 ohms Z0, and present two 200 ohm sources in parallel at what we thought would be the 12.5 ohm end.

The only place where it would be a real 1:4 would be where the transmission lines were effectively zero length, and at all multiples of 1/2 wavelength.

Of course if our definition of "work" is so sloppy that we think a single core 4:1 current balun "works" as a balun, then there is no reason to think that a 50 ohm to 100 ohm balun "works" to replace a 50 ohm to 12.5 ohm balun. :-)

Steel wool also "works" as a balun, if we use "work" sloppily enough.

The bigger question for me is how do we undo the harm done to technology when we repeat errors in technical articles, and why aren't things properly reviewed before print?

73 Tom
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on September 3, 2010 Mail this to a friend!
To Tom W8JI,
I now recall, not only having read your material about the single-core balun, but even printed it out.
I wish now that I had remembered it and included the link to your site to present your facts. It should have been there.
Also, no question that I need a better note-system to help compensate for my old age.
73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on September 3, 2010 Mail this to a friend!
To Tom W8JI,
I had this afterthought after I powered down the computer.
I'd contact the ArticlesManager about making a correction to the line 15 material to include comments like you presented about limitations of the single-core balun just so errors would not be propagated.
73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JI on September 3, 2010 Mail this to a friend!
Hi Jerry,

I hope I didn't come across as unduly rough about this, but the stuff about being able to build a single core 4:1 current balun really is a disservice to people building or purchasing baluns. It really doesn't belong in any technical article, because a single core balun with two transmission lines on one common core isn't a balun at all.

I measured baluns on a real nearly perfect dipole, and found the following on bands between 80 meters and 15 meters:

A popular single core 4:1 commercial current balun I measured had a current unbalance ranging between 10% and 80% from 3.5 to 21 MHz. On some frequencies this type of balun fed the antenna more like a "T" than a dipole!! On frequencies where scalar current levels were close, phase was far off. I might just as well have tied the feeders together and fed the antenna like a longwire on some frequencies as to use that type of balun. On a few "sweet frequencies" it was marginally OK, but on most it was poor.

A higher quality dual-transformer 4:1 balun had an unbalance ranging from 1% to 4% over the same frequency range on the very same antenna!! The dual core was twice as good on the dual core's poorest frequencies as the single core was on the single core's very best spots.

This is a startling difference, and being measured on a real antenna there is little room for argument that a 4:1 single core transmission line current balun is somehow a good idea. This of course repeats on a proper dummy load and on a spice model.

A paper analysis says it is a bad idea, a SPICE model indicates it is a bad idea, a proper dummy load shows it is a bad idea, and a real nearly perfect antenna shows it is a bad idea also.

It gets a bit frustrating to see something so technically ludicrous, and so easy to prove bad, presented over the years as a good idea.

73 Tom



 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on September 3, 2010 Mail this to a friend!
Tom W8JI,

No problem about the language; I say call'em as you see'em. We'll all be better for it when the dust settles.

The ironic and 'funny' thing about the single-core balun topic is that I stuck that in at the absolute last minute just to show there was such a concept. Oh well!

After I study some of your material in detail, I'd like to get back to you with some questions, especially about modeling circuits as I have a strong interest in that, having done it for half a lifetime with crystal and LC filters.

73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 4, 2010 Mail this to a friend!
A short response to KM3K.

I used a much older text, written many, many years ago by John Ryder. Good that you've spent plenty of time with other textbooks and some fine instruments.

I'll leave you with just one challenge. Sort of a proof by contradiction.

If, indeed, there isn't transformer action in your examples and that of Sevick, then 1) turns ratios wouldn't matter, since those involve transformer action; 2)The presence of a core wouldn't matter, since one wouldn't be needed as flux density wouldn't matter; 3) The sense or direction of multiple windings would not matter; and finally 4) Perhaps, most importantly, what Tom, JI reminds you, that attempting two baluns on one core wouldn't be a problem since there would be no magnetic field interaction between them in the core.

On the other hand, what would matter, for transmission line involvement, would be 1) Z0 of each length. Or, more simply, wire size, wire spacing and to a degree, the dielectric between them; 2) The length of each transmission line so as to achieve specific impedance transformation ratios desired.

Good luck with your designs. I suggested use of an MFJ-259B since it is a very affordable instrument and perhaps the most useful instrument I've personally ever owned besides an RLC bridge. Although it isn't cheap, it allows those of us interested in getting the most out of our antennas and feedlines an affordable opportunity to do them right.

73.

Lee
W6EM

 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JI on September 4, 2010 Mail this to a friend!
RE: Reply by W6EM on September 4, 2010

Some comments I'd like to add below.......

Lee Wrote::
<<<<If, indeed, there isn't transformer action in your examples and that of Sevick, then 1) turns ratios wouldn't matter, since those involve transformer action; 2)The presence of a core wouldn't matter, since one wouldn't be needed as flux density wouldn't matter; 3) The sense or direction of multiple windings would not matter; and finally 4) Perhaps, most importantly, what Tom, JI reminds you, that attempting two baluns on one core wouldn't be a problem since there would be no magnetic field interaction between them in the core. >>>>

I agree with your points above Lee. One of the errors that has always bothered me is the book appears to claim there is no "transformer action" or core flux, just because it calls a certain device a transmission line balun. If the core had zero flux, with energy totally confined to the transmission line, we could remove the core with no performance change.

There has to be core flux, or we would not need the core. That a simple but etched-in-stone truth!

If you review my explanation of why a single core 4:1 current balun with transmission lines cannot be built (at least so it works as a balun), you will see my analysis treats each transmission line section as a 1:1 ratio transformer.

http://www.w8ji.com/balun_single_core_41_analysis.htm

I actually open with explaining how the system has two distinct modes, and then repeat it again. It is a critical area we must understand, otherwise we cannot understand the balun.

Another critical area is the understanding of why a balun is needed. In Chapter 1, the book shows a clear misunderstanding of why a balun is needed. An antenna was tested that, because of feedline length, had virtually no common mode. The conclusion was a dipole needs no balun if the feedline comes away at right angles!

The second paragraph on page 2 of the 2002 printing is wrong. Diameter of the coax or "S" has nothing to do with why a balun is or is not needed. If I use 1-1/4 inch Heliax or RG174, it makes no difference on HF in need for a balun. S is totally meaningless at lower VHF and lower, because any reasonable size cable has a negligible diameter in wavelengths. The entire balance issue comes from the terminal VOLTAGES at the antenna, not the feedline diameter. S is meaningless.

Any dipole or beam antenna at .15 wave height to perhaps .30 wave height, if the cable is grounded ONLY at earth, needs no balun. Yet the text claims there is a difference because one antenna is a beam and one a dipole, and that makes no sense at all.

If you read down through my analysis, I show why some dipoles (and Yagi's) with specific feedline lengths and routing do not need a balun.

We have to understand what the load really looks like and what the balun really does, or we will come up with some very wrong theories and explanations....and even some balun designs that are not even baluns.


73 Tom
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by KM3K on September 4, 2010 Mail this to a friend!
Tom W8JI,

You have written, "One of the errors that has always bothered me is the book appears to claim there is no "transformer action" or core flux, just because it calls a certain device a transmission line balun. If the core had zero flux, with energy totally confined to the transmission line, we could remove the core with no performance change.
There has to be core flux, or we would not need the core. That a simple but etched-in-stone truth!"

In writing above "...or we would not need the core", you have really touched on something with which I have been struggling for quite sometime.

In fact, a month ago N2EY and myself had an interchange relative to my article about "1:1 Guanella-balun" in which I sort of allude to that struggle.
Not one ham has come back with any reply about the "core improves frequency-response" conundrum in that posting.
Here below is a copy of part of the interchange.

----------------------------------
N2EY: The Guanella current balun designs are such that they don't require a large part of the energy being transferred from the unbalanced side to the balanced side, or vice-versa, to go through the magnetic balun core.
The core only exists to reduce common-mode RF.

KM3K: IMHO the word “only” should be removed; Sevick has a plot showing a core improves the overall frequency-response but he makes no attempt to explain the mechanism to account for this improvement. It'd be nice to know what the cause is.
------------------------------

Sevick's plot is in Transmission-Line-Transformers 4th ed on pg 3-13 for a Ruthroff 1:4 balun with and without an unspecified core but no explanation is provided to the reader as to why the frequency-response improved so drastically with the core.
Sevick claims there is flux in the core for the low end of the frequency-response because convential transformer action dominates there.
But even for that extensive portion of the frequency-response where the transmission-line mode is operative, I quite agree with you that there seems to be some flux in the core; after all, over and over again in his books, Sevick makes a big deal about using low permeability cores.

I think the final chapters about baluns are yet to be written.

73 Jerry KM3K
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 5, 2010 Mail this to a friend!
KM3K:"Sevick's plot is in Transmission-Line-Transformers 4th ed on pg 3-13 for a Ruthroff 1:4 balun with and without an unspecified core but no explanation is provided to the reader as to why the frequency-response improved so drastically with the core."

Perhaps the answer could be found in early experiments of Sevick's former employer, AT&T, in their development of the "telephone network," vernacular for the CT used in conventional telephones to force equal and opposite audio currents and maintain the delicate balance of the telephone system.

Cores, in general, and especially torodial ones, help to confine magnetic flux.
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JI on September 6, 2010 Mail this to a friend!
Hi Jerry,

The flux density in the core does vary with frequency, number of turns, core material used, and the load's VOLTAGE from each balun terminal to ground.

If you look at the drawings on this page:

http://www.w8ji.com/balun_single_core_41_analysis.htm

you will see the voltages across each winding (transmission line conductor) for each core depends entirely on load voltage distribution.

The magnetizing current required to allow that voltage to exist depends entirely on the impedance of each winding on the core.

Obviously if we did not have enough impedance, the current would become very high or the antenna would come out of balance and NOT be able to supply equal and opposite currents to each feedline conductor.

Since the winding impedance increases with frequency (below the frequency where the winding becomes self-resonant), the core obviously is needed more on the lower frequencies. On higher frequencies just the self-inductance of an air core transformer would be enough to keep magnetizing currents to reasonable levels.

This does NOT mean the core has no flux at higher frequencies!!! It just means the flux, being proportional to magnetizing current, generally decreases as frequency is increased for the same voltage from each balun terminal to ground.

This is where I have a big problem with what otherwise is a very good handbook. The book seems to not grasp the concept of load balance. It becomes very clear reading Chapter 1 that the workings and requirements for balance in antenna and transmission line systems was misunderstood. This threw a monkey wrench in some of the theoretical solutions and technical explanations later, and is the root cause of the misplaced notion that a single core or stack of cores acting as one larger core can be used to support multiple transmission lines.

If a single floating resistor is used to test the balun, it does not test the balun at all!!! A single resistor floating from ground is neither balanced nor unbalanced, because the ratio of common mode current to differential mode current is always near infinite!

A single small resistor of the proper value works equally well up through VHF and UHF as a load for a 50 ohm coaxial cable, or a 300 ohm balanced system. It isn't until the resistor is a large fraction of a wavelength in size that it has ability to support common mode current and be sensitive to load balance.

None of the balancing devices in that book were tested with a proper load, and so any misplaced notions about balance were never caught.

I think the best thing is to put an article up about balance in systems so we understand what actually determines balance. If we don't understand that, we can't possible understand what works and what doesn't work to balance a system or how to test balance, or how a balun really works.

73 Tom
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JI on September 6, 2010 Mail this to a friend!
By the way, in 1983 I wrote a manual for the ATR8B antenna tuner.

It says:

"The ATR8B has a built in balun to provide maximum power into balanced feeders of either twin lead or open wire type. The balun provides a ground isolated balanced current source that is superior to conventional center-tapped voltage source baluns."
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by VE3EGA on September 6, 2010 Mail this to a friend!
Hi - you wrote:

//I have built this balun a few times feeding twinlead to my attic dipole (52 ft. flat top) with fairly good results. My rigs internal tuner will tune this setup on 10-40 meters, though I do notice some SWR rise during longer transmissions at higher power (75-100 watts).//

My response: The rise in SWR usually indicates that the core material is saturating. May be too small or iron wrong mix?

I prefer to use the AMIDON RED Cores for my current baluns..

Hope this helps solve your mystery?

73

Terry

ve3ega
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 7, 2010 Mail this to a friend!
Good point about the core.

I used to use the T200/240 mix 2, but found the FT240-61 to be ideal. It has an AL of 170 as opposed to an AL of 12 for the T200-2.

Its another dollar more, but considering I just bought some magnet wire at $15.00 a pound, ouch!!!! You could save enough wire to make it worthwhile. :-)

One other suggestion. The wire enamel is tough, but with the rough surface of ferrite, be sure to wrap the core with Scotch 27 or better, Scotch 69. 69 is the really good, fiberglass class H temperature tape. Tan as opposed to white color.

For small quantities, I've had good luck with www.kitsandparts.com. It is usually a better price than Amidon.

Lee
W6EM
 
How a 1:4 Guanella-Balun (Current-Balun) Operates  
by G6UWK on September 7, 2010 Mail this to a friend!
Well done Jerry

I would imagine there are a few like me with a Power Electrical background and RF behaves very differently than what we would otherwise expect.

Thanks for an informative article.

Jon
G6UWK
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W8JI on September 7, 2010 Mail this to a friend!
Lee,

Core heating rarely if ever has anything to do with saturation. It is commonly attributed to saturation, but the effect you see is virtually always caused by the loss tangent in the core making heat.

Think back to what the discussion was about, and the voltage across the windings that forces common mode current through the winding. The effect of that voltage across the winding (end-to-end) is the resistivity of the core is in parallel with that voltage and dissipates some power.

The core will overheat from that dissipation LONG before it approaches saturation, and if it reaches the Curie temperature the core in the hot areas will abruptly lose magnetic properties. Nowhere does saturation come into this. It is heat in a resistance and the Curie temperature, and that is why it takes time.

You actually proved the core is necessary, and has time-varying flux. :-)

Look at:

http://www.fair-rite.com/newfair/materials.htm

You are using a 61 material, which has a Q of 1 at 30-40 MHz. That means if you had a winding with 3000 ohms of reactance, there would be the equivalent of a 3,000 ohm resistor across that winding.

The real cure for this problem is a core with higher Q, a core with a higher curie temperature, more turns on the core so the resistance appears to be higher, or a core that gets rid of heat better. Any combination of these things might be required.

A 67 material would have more inductance for a given amount of resistance (higher Q). While it would require more turns, the heat would be less. You might just get away with the 61 with more turns, or better ventilation.

It is virtually never saturation. (If it was saturation, the SWR would instantly start to increase at a certain power level.) It virtually always is a resistance issue and power dissipation in that resistance.

73 Tom
 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by W6EM on September 8, 2010 Mail this to a friend!
Tom:

Aha. Well, with anything you put in the core, therein lies the rub. Thanks for the correction. Yes, indeed, if it were saturation, it would be power related. He didn't say, but as you comment, it may very well be frequency related.

The performance of the ferrite materials as you say varies significantly and one has to look at that in choosing which mix to use for bands of interest and power levels.

Is there a ferrite mix that can realize a satisfactory 80-10M choke balun of, say, the FT240 size core?

I've played with mix 43 for a low power voltage balun and that seemed to perform well on 75 and 40. A much higher AL.

Lee

 
RE: How a 1:4 Guanella-Balun (Current-Balun) Operates  
by WI7B on September 10, 2010 Mail this to a friend!
Great article, Jerry !

73,

---* Ken
 
RE: Ferrite Core Choices  
by W6EM on September 12, 2010 Mail this to a friend!
From what I've read, mix 61 is suitable for 80-30 meters. Mix 67 for 20-10m. As for 160, mix 43 might work, but it's AL is so high and temperature stability so low (16,000ppm per degree C), well....

There is a decent lower frequency iron powder core mix 1, which has an AL of about 250 down in the 1-2MHz range for a T-200 core. I used one of those for a choke balun for my 160M dipole.

I also found a reel of 1000 feet of AWG 14 teflon tube, which will come to good use. Teflon-sleeved AWG 14 wound bifilar works out to a Z0 of about 120 ohms.
Ideal for a 1:4.
 
RE: Ferrite Core Choices  
by G3TXQ on September 22, 2010 Mail this to a friend!
I've come late to this discussion, but I would make a couple of points:

No matter what the load configuration on a 4:1 Guanella balun, the common-mode voltage across the two chokes must be equal to the differential input voltage. Even when the load is fully floating, Vp1p3=V12+V43 in Figure 3.

This is quite different from a 1:1 current balun where a fully floating load would result in zero common-mode voltage across the choke.

It's easy to show that some load configurations can stress one of the two chokes with a common-mode voltage which is twice the input voltage.

Type 61 material is a poor choice for broadband chokes in the low-HF range; it typically produces narrow-band reactive chokes:
http://www.karinya.net/g3txq/chokes/

Steve G3TXQ
 
RE: Ferrite Core Choices  
by WA2JJH on October 5, 2010 Mail this to a friend!
The current balun will make a cheap vertial kick butt.
A counterpose or a few radials per band......SSB and CW
will really kick butt,
 
Email Subscription
You are not subscribed to discussions on this article.

Subscribe!
My Subscriptions
Subscriptions Help

Related News & Articles
How a 1:4 Guanella-Balun (Current-Balun) Operates


Other Editorial Articles
Combining Amateur Radio and American History
Great Way to Give Back to Our Hobby
How a 1:4 Guanella-Balun (Current-Balun) Operates