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Author Topic: 1:1 Balun  (Read 18525 times)
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flintstone mop
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« on: November 03, 2008, 12:14:47 PM »

Hi Folks
I'm a little lazy plus hurtin from a prostate biopsy today. Is there any way besides using the ferrite beads on the coax to make a 1:1 balun for 160M? Making a 6 inch diameter coil XXX number of turns(?). Like we use for a Yagi?Huh....yes...no??
This is for my vertical. It is good for isolating the antenna system from the transmission line. My previous balun took on water and everything went to hell. It was one of those RG174 types with the beads and the heat-shrink. I tried to weatherize the PL259's but the dam thing was water logged when I disassembled, looking for an open circuit trouble.

Fred
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Fred KC4MOP
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« Reply #1 on: November 03, 2008, 12:37:25 PM »


Fred,

I've used the 'Ugly Balun' before with good results:

http://www.hamuniverse.com/balun.html

Karl
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WU2D
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CW is just a narrower version of AM


« Reply #2 on: November 03, 2008, 01:41:03 PM »

Fred,

I assume that you are feeding a dipole? That ugly balun design is a good idea and you could improve it by making the Balun a replaceable component.  Adding a PL-259 and some strain relief on the coax feed side and mounting a pair of theaded eyes up top for the dipole would make a cool design. At 160M, coax loss is such a non-factor that you can probably just wind it with RG-58 and save weight. It should beat what you had before. If it is strictly for 160M, add some coax length.

Mike WU2D
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These are the good old days of AM
Steve - WB3HUZ
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« Reply #3 on: November 03, 2008, 02:45:41 PM »

You don't want a balun, if it's for your vertical. You are looking to choke off the common mode currents. Ferrite cores on the feedline is probably your best bet.
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flintstone mop
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« Reply #4 on: November 03, 2008, 04:09:28 PM »

OK Steve and gang
It's for the vertical and I'll have to get some ferrite cores on there. ARRL handbook has a section for baluns,chokes, etc and it looks like I needs 50 #73 material.

Thanks

fred
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Fred KC4MOP
Steve - WB3HUZ
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« Reply #5 on: November 03, 2008, 04:39:04 PM »

Or you can try this.

http://www.radioworks.com/ct-4.html


Why do you think you need this?
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Mike/W8BAC
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« Reply #6 on: November 03, 2008, 06:18:36 PM »

Fred,

Don't discount the coax coil so easy. The so called Collins balun works very well for common mode current problems. I have used it many times. Not only on antennas but between finicky solid state rigs and amplifiers. They don't need to be made from fancy supplies. Rule of thumb, Six turns of RG-8 or similar coax coiled with a six inch inside diameter. That's it.  As it said in the one web site listed here, separate the first coil and the last coil or stack the coils. That's it. Give it a try before you spend good money for a gizmo. Don't take my word for it, Tennadyne could have sold a gizmo for it's line of log antennas but they recommend the coax coil for feed line common mod current mitigation.

Mike
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Steve - WB3HUZ
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« Reply #7 on: November 03, 2008, 06:27:12 PM »

Most of those air-wound  types do not have enough series (choke) impedance on 160 meters. You need to use ferrites or a bunch more coax turns (and then it may get resonant on the higher bands).


http://www.k1ttt.net/technote/airbalun.html
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Steve - WB3HUZ
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« Reply #8 on: November 03, 2008, 06:40:23 PM »

An excellent source on common-mode chokes for all types of applications.

* CommonModeChokesW1HIS2006Apr06.pdf (1985.7 KB - downloaded 372 times.)
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Mike/W8BAC
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« Reply #9 on: November 03, 2008, 07:05:59 PM »

Steve,

I don't see anything in SRQ's results that would lead me to the conclusions you have made. what I recommend is giving the coax balun a try before buying a ferrite gizmo.

No vector impedance meter here. Just a few years on 160 QRO using the coil method with nominal results. Nothing ventured, nothing gained.

Mike
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Steve - WB3HUZ
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« Reply #10 on: November 03, 2008, 07:34:29 PM »

Quote
All the baluns start out looking inductive at low frequencies, as
indicated by the positive phase angles.  As the frequency is
increased, a point is reached where the capacitance between the
windings forms a parallel resonance with the coil's inductance.  Above
this frequency, the winding reactance is reduced by this capacitance.
The interwinding capacitance increases with the number of turns and
the diameter of the turns, so "more is not always better". 

The effects of a large increase in interwinding capacitance is evident
in the measurements on the balun with the bunched turns.  This is
probably a result of the first and last turns of the coil being much
closer together than the single-layer coil.

An important requirement of these baluns is that the magnitude of the
winding reactance be much greater than the load impedance.  In the
case of a 50 ohm balanced antenna, the balun's winding impedance is
effectively shunted across one half the 50 ohm load impedance, or 25
ohms.  A reasonable critera for the balun's winding impedance for
negligible common mode current in the shield is that it be at least 20
times this, or 500 ohms.

And
Quote
Magnitude in ohms, phase angle in degrees, as a function of frequency
in Hz, for various baluns.

            6 Turns    12 Turns     4 Turns     8 Turns     8 Turns    Ferrite
           4-1/4 in    4-1/4 in    6-5/8 in    6-5/8 in    6-5/8 in     beads
          sngl layer  sngl layer  sngl layer  sngl layer    bunched    (Aztec)
          ----------  ----------  ----------  ----------  ----------  ----------
Frequency  Mag Phase   Mag Phase   Mag Phase   Mag Phase   Mag Phase   Mag Phase
1.00E+06    26  88.1    65  89.2    26  88.3    74  89.2    94  89.3   416  78.1
2.00E+06    51  88.7   131  89.3    52  88.8   150  89.3   202  89.2   795  56.1




None of the air-core types come close to the 500 Ohm requirement on 160 meters. This is not to say an air-core won't work. We haven't defined what "work" means since Fred has not defined his requirements. I still want to know why he thinks he need a choke.
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flintstone mop
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« Reply #11 on: November 03, 2008, 08:14:53 PM »

Why do I need a balun?
I just thought it was part of engineering  a system together. Common practice, so to speak. I'm possibly reading too many ads or hype that read it's must to prevent "feedline radiation" and to "isolate" the antenna from the transmission line. All of these things that are bad ju-ju in an antenna system. These gizmos give that extra S-unit of signal..............right?Huh
I know that with my possible defective W2DU 1:1 out of the circuit I have almost 1:1 SWR and 52 ohm resistance and 0 reactance (the MFJ259 told me so) The numbers are too good to be true. Some air-time will prove it out.
Before my troubleshooting for the intermittent open circuit, and the balun in circuit, I had a 1.7:1 SWR and 37 ohms resistance and 20 ohms reactance. It looked more like characteristics of a vertical. BTW I have 10kcs of bandwidth between the 2:1 points.
How does K4KYV obtain 40-over signals by running legal limit??? He must have one of these gizmos somewhere in his station.......................hi
Fred
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Fred KC4MOP
Steve - WB3HUZ
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« Reply #12 on: November 03, 2008, 08:16:44 PM »

Quote
I know that with my possible defective W2DU 1:1 out of the circuit I have almost 1:1 SWR and 52 ohm resistance and 0 reactance (the MFJ259 told me so) The numbers are too good to be true. Some air-time will prove it out.


Where did you measure this? In the shack or at the antenna?
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Jim, W5JO
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« Reply #13 on: November 03, 2008, 08:28:24 PM »

Two thing Fred.

Put a 50 ohm non-inductive resistor across the terminals of the 259B and see what it reads.  Then put a cap in series with the resistor and see if the 259B agrees with the calculated impedance. 

The diodes in the 259B are real easy to blow and if that happens, your readings will be wrong.  Just hooking the 259B to an antenna with the wind blowing can introduce enough static electricity to get one or more of the diodes.

Other thing is that if you operate off the design frequency of the antenna there is going to be unbalance.  It doesn't matter if you use ladder line or coax, it will happen.  How great the magnitude will be proportional to the deviation from the center frequency and the result can be current on the shield.

Just install a great radial field, meaning be sure it is connected very well and, if you move very far off frequency, then have a good way to either tune the base of your vertical or be prepared for current on the line.
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flintstone mop
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« Reply #14 on: November 03, 2008, 08:53:36 PM »

Good points here, Steve and Jim.
I know in the dummy load the MFJ reads true, I'll try the capacitor in series.

There were two readings. I guess I gave the one in the shack. As the perfect reading. At the base of the antenna there was 1.5:1 SWR and the same 52 or 53 ohms and 10 ohms reactance. The transmission line is acting as a transformer. Before I cut out the W2DU balun the reading was the same at the antenna and in the shack. Which makes the coax look like a transmission line, not a transformer.

Fred
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Fred KC4MOP
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« Reply #15 on: November 03, 2008, 09:54:24 PM »

Fred im gonna take a stab at this if im off base slap me.  As a money making scheme  out of highscrewel I bought an invisible dog fence trencher. installs light guage wire about 1-4 inches down.  I put up an add at my local hro.  I install verticals and radial fiends.  I actually bought a brand new 1994 dodge shadow doing this.  anyway I learned a little bit about verticals.  As we all know ground resistance number of radials yada yada affect the impedance. and that can be furthur corrected by placing a coil from radiator to ground.  Like the butternut does.  If your w2(my henry8k will fryit balun) is for a better match Might i sugguest getting about 40 ft of #14 magnet wire and downlading the install manuel for the hf6v. experimet with the coil its about 1.5 inch in diameter

I am ass oom ing that this vertical is ground mounted and has radials at surface level or less than an inch down.  I am also assuming that the end of the radials are at least 20 feet from the house.  One of the things i found out early on for ground mounted verticals is that if the feed line goes into the ground as close to the feed point as possible and goes down at least 12 inches deep for at least 10 feet past the end of the radial feild and the ant is resonant. common mode current problems began to dissapear.  In reading and talking to some old engineers the only thing i could come up with was in the near field if the feed line was allowed to be to close to the surface it just became another radial that just happened to travel straight into the shack. It also appeared to be very importtant to have a real 8ft ground rod at the ant with only a few inch long strap to the co-ass.

aint nothin scientific about the preceeding statement its just what worked for me after a long summer of trial and error.  word got around and i can put a friggin butternut or a gap anything together blindfolded..
I REALLY SHOULD HIRE AB2EZ TO DO MY TECHNICAL RIGHTING LOL

still have the trencher http://videos.eztrench.com/?cat=1
play the last video on the page..


ok DR HUZ Rip me a new one and tell me where im wrong
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steve_qix
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« Reply #16 on: November 04, 2008, 06:23:45 AM »

Hmmmmmmmmm.... a BALUN (balanced-to-unbalanced) for a *VERTICAL* ??  Wink

If you're truely running a vertical, I cannot see the need for a balun.  Baluns are generally used for balanced antennas (which a vertical is not), where you have an UNbalanced feed (like coax) feeding the balanced radiator.

I have worked with numerous verticals in the broadcast industry (I don't use a vertical myself in amateur radio at this time), and there was never, ever, a balun.  Just a matching network to match the 50 ohm coax to the antenna, which was never 50 ohms.

Anyway, it is possible I'm missing something here (quite possible), but otherwise, I can't find a good technical reason for needing a balun with a vertical antenna.  It's just something else in the system to dissipate power !!

Regards,

Steve
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« Reply #17 on: November 04, 2008, 08:09:20 AM »

Ive made it a point to use ferrite sleeve baluns since the 80's since coax baluns didnt seem to work very well on any band.

With coax on various mono and triband yagis I had TVI/RFI in the neighborhood at 1200W, ferrite solved those problems. Its easy to see why by looking at a vector impedence analyzer which I had access to at work and could tailor the performance. I did some of the early analysis for the YCCC newsletter. Many I talked to switched to ferrite and were amazed at the TVI/RFI improvement, especially on a TA-33 and similar in a dense (housing, not people) neighborhood.

One thing that stood out in the lab tests was that the little beads over small Teflon cable werent of sufficient impedence to be effective below 40M. Using the long fat 43 Mix beads 1.5" L x 1" W and filling up 12" of RG-213 did the trick from 160-10M. Mix 61 was a wash on 15M and better on 10/12M but the 43 was still quite effective. I use Mix 61 on 6M.

The large beads dont heat up or cause any non linearities at any power level Ive been able to generate when repairing and testing some customers big amps.

With phased verticals on 80/160 the front to back wasnt what I expected with direct coax feed. With ferrites the directivity was much improved. I was using simple relay switching with coax phasing lines for end fire cardioid or a figure 8 broadside. No fancy and expensive tuning networks needed, just a small investment in ferrites.

With a 4el 40M KLM I tried coax and commercial baluns before the sleeve balun was publicized. It was not a good performer in either direction. A ferrite sleeve balun turned it into a pileup buster.

Carl
KM1H
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flintstone mop
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« Reply #18 on: November 04, 2008, 09:26:10 AM »

Hello All,
Thanks for many valuable thoughts and comments. And Bill, how much is that invisible dog fence device??? Sounds like the perfect way to lay a lot of radials without a lot of bending, stooping, and stomping the sod staple into the ground. I have another vertical to repair prolly in Spring before the the foliage returns.

I have 35 radials so far just laying on the ground. 100 feet long. Held down by sod staples. The radials should magically disappear next Summer as the grass starts growing again. I'd like to lay about 10-15 more. Working with MaNature's dirt and roots and rocks I cannot bury the coax. This antenna is about 400 feet from the house in a moist area, nothing much around to mess it up. I'll get a pic posted of this installation.

The ferrite beaded coax are listed in The Wireman as a 1:1 current balun. They are for isolation. UN-fortunately this beaded coax is branded as a balun.
I'll assume that b'cast stations bury their transmission lines and the radials are under several inches of soil. Bill might have a valuable point about burying the transmission line to reduce exposure to the RF field.
All I can say is that the MFJ readings are the same at the base of the vertical and in the shack with the current balun in circuit. The current balun out of the circuit I get two differnt readings as was posted earlier and an on-air test would reveal probably no difference in received signal level to a distant receiver. I'll step in some soft muddy dirt here and say that I think the vertical is little quieter for receiving with the current balun in circuit.

A very helpful tech at Cushcraft told me about the coil trick (connected between the hot side of the vert and ground.) and that helped me to get the antenna in the ball park. That acts as a type of transformer(?)
Thanks for the great input.
BTW I heard the TRON on 160M with a very nice signal. 10-3-2008 around 9PM.

Fred
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Fred KC4MOP
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Rick & "Roosevelt"


« Reply #19 on: November 04, 2008, 10:24:22 AM »

Fred,
Hope the biopsy results work out well.  We're all rootin' fer ya.
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Steve - WB3HUZ
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« Reply #20 on: November 04, 2008, 11:00:03 AM »

Quote
Which makes the coax look like a transmission line, not a transformer.


Nah. The coax will act as a transformer with the balun in the circuit too. Now, if the impedance is 50 Ohm and zero reactance at the antenna, then yes, you will see 50 Ohms in the shack, no matter the length of the feedline (well almost, at some point the feedline loss will change things). If your coax is one-half wavelength long, then you will read the same at the antenna and the shack, even if if the Z at the antenna is not 50 Ohms.

Mikey is on to something. If you can bury your coax for a good distance from the shack, common-mode problems should be reduced. This is what I do with my K9AY loop system. I also use a bunch of ferrites around the coax too. I'm doing it to prevent the common-mode noise from degrading the SNR.

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flintstone mop
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« Reply #21 on: November 04, 2008, 03:30:17 PM »

Thanks Rick
For the biopsy thoughts. MAN that was not goodness!!! 12 DAM times he kept snatchin something from my body. It's down hill after 50..............
Fred
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Fred KC4MOP
Jim, W5JO
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« Reply #22 on: November 04, 2008, 06:03:06 PM »


For the biopsy thoughts. MAN that was not goodness!!! 12 DAM times he kept snatchin something from my body. It's down hill after 50..............
Fred

Wait a few years Fred and you will wonder if they will be able to bury you in a shoe box.

Remember 50 is supposed to be the new 40.

Put your sleeve beads at the base of your antenna and then an equal number where the coax enters the shack.
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flintstone mop
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« Reply #23 on: November 04, 2008, 06:44:54 PM »

OK Thanks
I keep forgetting that, through the modern miracle of medicine, we are now supposed to go another ten years. And they want to raise the social security age too. ooooops there goes the thread
Fred
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Fred KC4MOP
ab3al
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« Reply #24 on: November 08, 2008, 08:33:01 PM »

Quote
Mikey is on to something. If you can bury your coax for a good distance from the shack, common-mode problems should be reduced. This is what I do with my K9AY loop system. I also use a bunch of ferrites around the coax too. I'm doing it to prevent the common-mode noise from degrading the SNR.

damn I got one right. 

fred the machine was $2700  not something to run out and buy for one ant.  Frankly for the sake of combating ground losses if you can live with the radial on the ground surface you are better off with them like that.

man i still cant believe it.. dr huz concurs.. my head is gonna swell up even biggers than Obama's
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