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Author Topic: Sweet Balun Idea  (Read 10254 times)
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WA4WAX
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« on: May 25, 2016, 11:50:22 AM »

Put this one on the INPUT of a balanced, low pass Pi or T tuner (Or L), and you will have a winner.

Pay careful attention to symmetry when you build the tuner.  Let the cap rotors float on the tuner, do not ground them. They will be at RF neutral (Virtual ground) if you do your job well.

OK, here we go.  This thing will be good for AT LEAST 750 watts on the HF bands.  Common mode suppression will be over 6000 ohms.

Shopping list:

24 multi-aperture 73 mix cores from Fair-Rite.  Mfg number 2873006802. Ok, 20 or 22 would likely be enough!



About 6 feet of hand formable UT-141.  Micro-coax number UT-141C-FORM-LL-F

Line up 24 cores end to end. Then line up another 24 on the first stack.  Bond them with zip ties or something.

Run the UT-141 through both holes on the bottom chain, then go through the top chain.  Form matched pigtails on one end.  Connectorize the other end.

Voila! 9,000 ohms on 10 MHz!  Even on 10 meters life will be good.

Choose 50 ohms for your tuner input.  Your output can be whatever.

The RF voltage burden is divided by two, so 2 KV spaced caps should handle just about anything.

Yes, you can box it up and use it for that vertical with radials.........or for that big log periodic.

You will be amazed at how a very high choke impedance will help you on receive.

Have fun!! When you are done, check balance with a VTVM.  Bet it will be better than 1%!!!

This is the W2DU balun on steroids. 

Matt :-)

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KD6VXI
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« Reply #1 on: May 25, 2016, 01:52:36 PM »

That is pretty much Richard Measures design,  is it not?

I've never built it,  but there are quite a few people that have,  and it seems they really like it.

Choke balun know the input,  works good.

--Shane
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WA4WAX
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« Reply #2 on: May 25, 2016, 02:32:29 PM »

Dear Shane:

I am not sure if Measures described this particular balun or not.  Please post if so.  The balun on the tuner input  idea is not mine; I am just describing a nice, high performance balun. I have yet to see someone use the binocular 73 mix cores and UT-141.

I could not find large 73 mix cores as they are not manufactured. I did did find the large binocular cores in 73 mix.  They will just pass UT-141.

I specified the hand foramable as it has a low bend radius.  One could use standard 141, but you will have a 4 or 5 inch loop after each pass.  Not a big deal.

Heating with this design should be negligible, even at high power levels.

The whole thing would go in a box about 28 inches long and 3 to 4 inches, 4 inches deep.

The key here is to show the beast a low load impedance.

50 ohms or less: Balance outstanding.

100 ohms: Still decent.  Probably OK for most Hams.

200 ohms: Marginal.

Over 200.........No go.

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KD6VXI
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« Reply #3 on: May 25, 2016, 04:45:15 PM »

OK on the binocular style,  he used beads. 

Lots of people experimenting on Wales original design now.   I saw a balun being discussed on another reflector that was amazing.....   And they had VNA plots to back the claims up.

Guy running a 3000 hasn't burned it up.....   Yet.   

--Shane
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WA4WAX
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« Reply #4 on: May 25, 2016, 05:02:03 PM »

Walt was a very close personal friend......and a mentor.  He was the best.

Walt used those little 73 mix beads.  They are marginal performers.  Unfortunately, they do not make big 73 mix beads, at least not to my knowledge.  However, those binocular cores are beefy.  :-)

I designed a quadrature drive circuit for MRI coils using his balun approach.  We tested the idea around 8 MHz on an old desk in his shop. 

My baluns are at work in the Magnet Lab at UF in Gainesville.  I ues a long string of 31 mix snap beads on RG-8X. Thirty of them. Big beads.  Each about 1.5 inches long.  They provide 7 or 8K of comon mode resistance.  Output is via a shielded balance line made from a matched pair of RG-223. Current balance is around 0.3 percent for a 50 ohm resistive load.

The transmission line resonator coils are built on copper clad Rexolite 1422.  Walt did not live to see the final embodiment, but did see some of the first images/spectra.
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Steve - K4HX
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« Reply #5 on: May 25, 2016, 11:11:55 PM »

Sounds interesting. Thanks for sharing. Not sure how you check the balance with a VTVM though.
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KD6VXI
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« Reply #6 on: May 26, 2016, 01:33:09 AM »

Sounds interesting. Thanks for sharing. Not sure how you check the balance with a VTVM though.

With an rf probe?   I know we normally look to rf ammeters,  but wouldn't voltage be just as good an indicator in owl?   Light bulbs say so....?

--Shane
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Steve - K4HX
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« Reply #7 on: May 26, 2016, 06:29:48 AM »

Sure, with an RF probe. Thanks for clarifying. I generally default to a scope. And yes, measuring current balance is more valuable for most antenna applications.
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WA4WAX
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« Reply #8 on: May 26, 2016, 09:43:05 AM »

Yes indeed!  RF probe.  Get out your 410B, or Hickok 209A, or what have you.  A scope is also good.  Put two matched, 25 ohm noninductive resistors in series.  Do not ground the intersection of the two, but use this point as a floating reference.  Now check the voltage across each resistor.  If you use a 410C or the HP vector voltmeter, you can plug a digital voltmeter into the output port in the back and make some really precise comparisons. 

Best instrument for balun checking is a vector voltmeter, but most Hams do not have one.    It is nice to be a have, having been a have not in my youth.  :-)

Here are some pictures of my monster W2DU style baluns used at the Magnet Lab.  It uses about 30 large 31 mix snap-on cores over RG-8X.  The current balance is great!  This baby would shine on 6 and 2, though it is a bit long.  You could shorten it by making a coax "haripin", provided the turn is not too tight.

I plan to swap 1/4 Heliax for the RG-8X one of these days.

I cannot say it enough: Get that sheath resistance at or above 5 or 6K!  You will be glad you did.


* Matt 258.JPG (1215 KB, 2816x2112 - viewed 565 times.)

* Matt 257.JPG (1206 KB, 2816x2112 - viewed 613 times.)
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KD6VXI
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« Reply #9 on: May 26, 2016, 01:12:54 PM »

Indeed Walt was a smart man,  and loved rf.   He and I had more than a few emails talking about a choke balun I was working with.   Using hardliners and fairly obscene power levels.   With watts help,  I got it out of all of the audio gear.

Jim Brown is another person who is good with chokes.

A VNA is high on my shopping list.   I'm leaning towards a minivna 3 ghz model.....   But the Mfj 225 is a 2 port,  has a display built in,  and I won't feel.so bad if I break it at 3 hundred bucks.

Anywho.   Time to get ready for work.

--Shane
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« Reply #10 on: May 26, 2016, 07:09:30 PM »

Sounds interesting. Thanks for sharing. Not sure how you check the balance with a VTVM though.

With an rf probe?   I know we normally look to rf ammeters,  but wouldn't voltage be just as good an indicator in owl?   Light bulbs say so....?

--Shane
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The TS-505 will do.
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« Reply #11 on: May 31, 2016, 08:48:44 AM »

Put this one on the INPUT of a balanced, low pass Pi or T tuner (Or L), and you will have a winner.
<snip>

You will be amazed at how a very high choke impedance will help you on receive.

<snip>

Matt :-)

Ok, please tell me what it will do on receive?

And, is there a picture or drawing of the one you are describing?

I see the very long, linear one in the thread...
...and also, forgetting about a tuner, IF ur not using a tuner, and have a coax fed dipole, what are we talking about then??

                 _-_- signed, no clue
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« Reply #12 on: May 31, 2016, 09:29:16 AM »

Of you have common mode noise / noise being brought in by  shield of the coax,  it has made a huge difference for people.

It divorces the feedline from the antenna.   Otherwise,  your feedline IS part of the antenna.

--Shane
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WBear2GCR
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« Reply #13 on: May 31, 2016, 02:57:00 PM »

Ok, so how would this be different than putting the coax through cores,or snapping cores around it?

And is not the idea of a balun to be a 1:1 transformer making both "halves" of the ant receive equal and opposite current & voltage... vs. the "ground side" of a coax fed ant "sitting" on ground and the energy on that section being more or less parasitic??

Also, if the "choke" is flying up in the air, it make that point look like a high-Z for whatever wants to go common mode from that point, but from there down, it's not looking like a shorted piece, and even if it was, at some freq a "stub" is not shorted... very confusing to me.

These things, honestly, have never been terribly clear in my mind... maybe if I spent some time actually reading about them I'd be less ignorant. Nah. :p

                  _-_-
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Steve - K4HX
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« Reply #14 on: May 31, 2016, 04:00:21 PM »

http://amfone.net/Amforum/index.php?topic=29786.msg231307#msg231307
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KD6VXI
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« Reply #15 on: May 31, 2016, 07:21:21 PM »

Bear,  it's really too bad Walt is gone.   I had the same questions as you,  and was lucky enough to have Walt spend some time with me over email.

It's not much,  if any different than a split core or regular core.   The best method I know of is 240 cores.   Those you can get 5 to 6 turns through,  depending on the pull lube and other variables.   

The choke / balun keeps rubbish off the outside of the feedline.   This keeps the antenna pattern what the models say it should be.   Otherwise,  near field can couple to the shield of the coasshole cable and radiate.

The opposite is also I  effect.   Without proper feedline divorce,  all the wall wart,  blenders,  VFD drives on AC u it's,  etc WILL couple to the shield,  and be brought right into your receiver.   Divorce the outside of the coass,  and your antenna at 100 feet high becomes the only source of rf for your receiver,  instead of the feedline contributing to it as well.

Jim Brown,  K9YC has an excellent pdf article with cookbook chokes,  curves,  sources,  part numbers and a lot more info than I can regurgitate from memory.   I don't have the url but Google will return it with k9yc choke book as the search term.

I've heard from others that they experienced a huge difference.   My personal anecdotal evidence is from. 11 meters.   They did decrease my background noise level.   The signal level stayed almost the same.   Some people where the same,  some slightly lower,  and some higher.   All within maybe an s unit.   The background noise level dropped a couple s units.  Sig to noise was a lot better.

Oh,  and I wasn't in my neighbors land line phone any longer.   I can't tell you about since I got my ticket.   I've just used them ever since.

I'm now completely OWL for hf.

--Shane
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« Reply #16 on: June 01, 2016, 10:08:01 AM »


Wow!  Shocked  That's some paper. Downloaded and printed, put in a folder, will be read several times through... tnx.

                 _-_-
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KD6VXI
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« Reply #17 on: June 01, 2016, 11:58:34 AM »

That's the paper I referenced as well.

You should look through everything Jim has done.   He's a member of SBE and others.   And freely shares his info.

Excellent articles on verticals,  low band antennas,  etc.   I've read and reread a lot of his stuff.

From one of his posts:

'

RFI/ EMC is a topic I started working on professionally around 2001. I'm
still vice-chair of the AES Standards Committee Working Group on EMC,
and am a principal author of all of our Standards on EMC. A lot of what
I know came from hanging out with some of the other very bright guys in
that WG.'


--Shane
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WA4WAX
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« Reply #18 on: June 01, 2016, 12:30:51 PM »

I second that on K9YC!  Great resource.

I am offering the binocular core design with 73 mix beads because it is a bit more compact. assuming you are not running high power.  It is a neat way of side stepping the need for a long string!

Here is how yesterday's test came out at 50 MHz on the balun pictured. 

Each output port was terminated with a 50 ohm precision load.  Thus, the total load on the balun ouput is 100 ohms.

Amplitude and phase were checked with a HP vector voltmeter.  A HP 608 supplied the RF.

Probe on center conductor terminal: RF voltage 1003 mV.  Phase set to 0 degrees.

Probe on shield terminal: RF voltage 1006 mV.  Phase reads 180 degrees spot on!

That is a current balance of about 0.3 percent.

How do they help on receive?  Signals are correlated.  Noise is not.  Thus, noise from each of the two balance terminals sums vectorially at the input terminal.  Since noise is not correlated, amplitude is diminished.
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Steve - K4HX
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« Reply #19 on: June 01, 2016, 07:24:20 PM »

Noise is reduced by reducing common mode current. Some common mode current will be the result of near field noise sources. Thus, receive noise may be reduced, if you have near field noise sources (hard not to these days). A balun is not strictly required though. Burying the feedline can reduce/kill common mode borne noise too (best in antennas close to the ground, like may receive antennas).

Another good read.

http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
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