Choke Balun Losses

[ka4koe]

I will eventually get around to assembling all the parts for a balanced tuna, based on W4MMQ's design....

http://ka4cid.blogspot.com/2008/12/w4mmq-legacy-balanced-antenna-tuner.html

In the interim, I plan to construct a cheap (3 or 4 dollars) coaxial ugly "choke" balun. The balun will transition the 600 ohm open wire to coax, which will then connect to the back of my Heath SA2060. The internal 4:1 balun is likely way, way undersized for my intended task. The balun would be wound on a 4" PVC conduit, around 25' total length of RG8U (9913), solid dielectric.

I've looked here and there and have not been able to get firm answers on the losses. I am not sure if one can use the loss calculator at

http://www.qsl.net/co8tw/Coax_Calculator.htm

For instance, using this calculator, 25' of RG8U (or 9913) running a 15:1 SWR @ 1.8 MHz yields a loss of 0.3 db. Am I on the right track, or are there other factors to consider??

Tnx.

Philip

[ka4koe]

These calcs deleted as they were in error. Imagine that!

[W2VW]

Are your figures taking the feedline transformation into account?

[Opcom]

If the idea is to go from a 50 Ohm coaxial connection into a balanced input of the tuner, and use the tuner to transform the 50 Ohm 'balanced' impedance to some other value at the far end, then a 1:1 "core type" balun made for the purpose ought work even better than the coax cable with beads or the coil of coax shown in the diagram.

I did not care for coax with ferrite beads on it, or coiled up coax,  being used as a balun because of losses and heating up the beads, but I'm not an expert on it. not at all.

I already got the round tuit for collecting the balanced tuner parts, but not the round tuit for making the antenna tuner, yet. The parts would make it substantially similar to the one in the article. - except for the planned use of a 1:1 toroid-core current balun on the 50 Ohm input side of the tuner instead of the coil of coax. 50:50 and let the matcher do the matching.

If you find his ferrite bead balun works well, please give the details on it.


p.s. the sole comment on that great article is a garbage spammer lying about a nonexistent tuner, to trick visitors into clicking on the link to his own commercial sales site. hate that. don't give it any clicks!

[ka4koe]

I'll notify my friend Mark, KA4CID about the spammer. He knew Ed quite well before he passed. I'll let you know how the balun works out. As they say down here, we're getting to the "short hairs".

[ka4koe]

Are your figures taking the feedline transformation into account?

Actually, the SWR run up above is erroneous as I noticed after the fact I modeled it in free space. I remodeled the system with the 600 ohm feed.

Here is the revised run with "real ground".

Philip

[ka4koe]

Another view. Spacing of feed conductors @ 4" for 600 ohm. You can actually see the feedline better in this overhead view.  40' vertical to 60' horizontal. It's not actually a sharp bend like that but a gentle curve. This run also does NOT show the balun at the feed. The feedpoint is indicated by the little red circle.

[ka4koe]

Ed also met Armstrong at one of the annual banquets of the Radio Club of America.....years ago, of course. One question I have never been able to have answered was whether or not Armstrong held an amateur license??

[W2VW]

Been up all night so maybe it's me. Are those impedance figures indicating the impedance at the shack end of the balanced line or the impedance of the antenna itself?

Ugly BalUn rule of thumb.
Choking impedance should equal at least 10 times the resistive impedance in the circus where the device is used. I have no idea how to treat reactance at that point.

The reactance of the coax coil is provided by the shield. Mostly inductive and some unintended capacitance as in any coil.

I would not expect one of those to do very well in high numerical resistive loads due to lack of reactance in the coil. In reactive loads it is possible the BalUn will share some silly circulating current with other matching components. This can lead to wasted power.

The sleeve ferrite deal might be a better solution here but the best solution IMO is to do exactly what the linked test suggests. Put the balun at the 50 ohm non-reactive A.K.A. j0 point of the circus.

Interesting similarity of that test with the AG6K Balanced Balanced tooner article.

Quite a bit of internet noise about how well baluns work in different situations. Remember to use the narrow filter when reading. The ugly balun should not be expected to work well from 1.8 all the way to 30 mhz. Better to use one for 40 and up. Enough turns to get dizzy on 160. Once again, sleeve ferrite designs work much better.   

That 2060 Heath is pretty good but the balun on output method is not always a good way to transfer power.

[K1JJ]

Using coax:

I think the bottom line is if we are to use coax in any situation, an attempt needs to be made to match the coax to its characteristic impedance, whether that be 50 ohms, 75 ohms or whatever.  The ferrite beads or coax coil is just incidental to the good practice of choking off any shield currents ONCE the coax is properly matched.

Running coax at high swr, even with choke or ferrite beads, can generate very high voltages or currents that can arc over or melt the coax when running KW power levels. (In addition to imbalances and wasted db)

Coax is best used for a single band - or for multiband use, to feed an adjustable tuner that in turn feeds open wire line.  The coax stays at 50 ohms J0 by constant proper matching.

There are a lot of gimmick antennas out there using coax in the system that twist good practices like pretzels.


T

[WD5JKO]

All good stuff here....

The new Polamar Engineering company has a product called a super choke:

http://palomar-engineers.com/baluns-and-ununs/1-1-balun-kits/super-choker


When I put up my 15m loop, I fed it with RG-8X in a corner. As a single band antenna it loaded up good, SWR was low, and signal reports were above average for ME. Then I got stupid and tried to put it on 20M with a tuner in the shack...Dumb. The thing loaded with my Heath 2060, and with a few hundred watts carrier, I let it soak for a few minutes. Up the ladder and touching the coax, it was REAL WARM! Using a CFL, I discovered that the coax was illuminating the bulb for at least 6' from the antenna. So adding insult to injury I added four type 43 1" long ferrite beads at the antenna end. The tuning solution changed a lot, and was very broad....Hmmm. So I did the 200 watt soak once again for several minutes. Up the ladder (RF Off), and I grabbed the line with beads. Those beads were like hot charcoal, burned me pretty good. Sometimes we are compelled to do something even when we know better.

Later on with OWL, and  Johnson MB, I made that antenna play on 40-15m, and on 80m it is a good receive antenna with improved S/N ratio.

Jim
Wd5JKO

[ka4koe]

Its the open feedline end BEFORE hooking up to a balun, Van De Graff, etc., near the shack. Just ran some figures on my old inverted L system.....matched in the shack (bad news in any event) with coax (worse news).

Here are the losses using the L.....

160 - 2 dB
80 - 6 dB
40 -5 dB

No wonder no one could hear me. Definitely in the PW category.

[Opcom]

Mea aeris filum ut funebribus circo. Mecum omnes plangite!

[ka4koe]

What really killed the L for me was simply no desire to build a remote network at the base capable of handling the output of my SB220; that and a continuous stream of verbiage from my station consisting primarily of "Can you hear me now?".

[W2VW]

Back to the original question.

Losses.

If the SWR is 10:1 for example and the power 1250 watts there can be 5 RF amperes at 50 ohms and 50 RF amperes somewhere along the part of the system run at 10:1.

Put a piece of RG-8 in line with AWG13 IIRC center conductor with 50 peak amps of current and season to taste.

No wonder baluns get a poor reputation with hobby radio people.

The answer is build the tuner as described 

If the modeling is tried out with slightly different feedline lengths it becomes obvious that the SWR across the whole 10 meter band will vary quite a bit. Things may not be as bad as they seem initially.

[aa5wg]

Philip,

To date no  company has manufactured a ceramic based balun that can tolerate variable impedance's without generating loss.  In many cases these baluns heat to the point of damage.

Chuck

[Opcom]

Philip,

To date no  company has manufactured a ceramic based balun that can tolerate variable impedance's without generating loss.  I many cases these baluns heat to the point of damage.

Chuck

I'd agree that is the key to using a ceramic based balun. A stack of them on a piece of coax can get hot as well.

[KD6VXI]

If your stack of beads is overheating,  you need more beads.

Walt's balance needs approximately 100 beads to work.

The problem most people have with the bead balance is not enough choke Z,  making it heat up instead of choke off.

Coils of coass with beads backing it up can help.   Beads for lower end of band,  6 inch turns,  5 to 6,  help with the upper bands.

--Shane
KD6VXI

[aa5wg]

Opcom said it correctly.  A stack of these beads can still heat up.  I did an experiment with a stack of beads and they got so hot the coax cable began to break down.  This was at 110 watts.  Thus far, a link antenna coupler seems like a great alternative to heat.

Don't forget that the coiled up coax choke balun is not balanced.  The total inductance of the shield vs. the inner conductor are different.

Chuck

[ka4koe]

More parts on the way to get this balanced tuna at least working. We can make it pretty "later". Will not be installing a balun on the load side of the tuna.

[KD6VXI]

Opcom said correctly.  A stack of these beads can still heat up.  I did an experiment with a stack of beads and they got so hot the coax cable began to break down.  This was at 110 watts.  Thus far, a link antenna coupler seems like a great alternative to heat.

Don't forget that the coiled up coax choke balun is not balanced.  The total inductance of the shield vs. the inner conductor are different.

Chuck

And how many beads did you use.

I've used a bead based choke at power levels that most people would crap their pants at.   With the direct help of Walt,  and reading K9YA as well as Rauch's pages,  and had no problems.   Pre bead choke,  bad problems with rf in the rack gear.   Post beads,  no more issues.

I used well over 100 beads,  though.   50 beads cracked.   

According to Walt,  on this board,  anything that chokes antenna currents off the outside of the coass is a balance,  as it is accomplishing the same thing.

--Shane
KD6VXI

[W2VW]

Shield and center conductor do not need equal inductance.

The concept is to impede current flow on the outside of the coax shield.

Some internetz writers state a sleeve or ugly balun isn't really a balun for some reason.

They are incorrect when the choking impedance is high enough at the frequency of interest.

I just replaced my balanced balanced tuner's input choke with sleeve ferrites. The 1:1 Radioworks unit I was using got warm after long transmissions. My porch lights have stopped blinking on 40 meters now. The Radioworks unit always served me well up to this point on all HF bands except 30 and 60. Didn't try it there.

Antenna tuner is now located 20 feet above physical ground and things are interesting to say the least. 

[ka4koe]

I've decided to build this tuna "old style" and install the parts on a nice piece of wood, about 18" square, give or take. I figure this is cheaper (4 bux for the board) than spending 90 bux for a fancy-smancy metal box.

Additional benefits.......increased buzzardly appearance.

A pair of RF ammeters to compare balanced antenna current would be cool as well, but we are getting ahead of ourselves at the moment.

[W2VW]

I suggest adding another roller inductor and DPDT svitch. Make it available exactly as you have done with the varicap.

You will not be disappointed with the range and performance of this project.

[ka4koe]

My bro KK4TVR asked me over the local 70 cm repeater today on the drive home…."are you going to put some idiot lights on it??"

I replied, "Why? You aren't going to be using it…"

OK, so you're suggesting another inductor (shunt L).