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Author Topic: Ladder Line to Coax  (Read 49052 times)
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flintstone mop
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« on: December 16, 2009, 03:30:34 PM »

Hello All,
I looked around the forum, and maybe this is a worn subject BUT:
I am pondering our visit to the Philippines and considering a VEE ant using locally available bamboo. This stuff can get pretty tall. I thought about 40 foot center and ends 20 feet high. Supporting the bamboo is still grinding in my head.
I am thinking of feeding with ladder line and transition to coax coz the tuner I'm taking with me is only for coax. Could I use a balun to make a transformation to the coax and work?

Thanks
Fred
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Fred KC4MOP
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« Reply #1 on: December 16, 2009, 03:50:14 PM »

Yep.   You can use a Balun to convert to the coax.  But your going to have some loss.  Lots of misinformed hams run coax out the shack to a wall or tower mounted balun. Then ladder line up the the antenna.  They do this to solv RFI issues that they think is comming from the balanced feed. 

For a temp Trip, I would say just take a G5RV. This will plug into your coax tuner and work anywhere.  ,Timtron used one on a late night AM QSO and it beat his big wires out here to AZ by a huge 10DB! 


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W2VW
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« Reply #2 on: December 17, 2009, 11:26:59 PM »

It again depends on what you mean by ladder line. 390 to 450 ohm line or 600?

A 4:1 balun will work ok with 450-ohm line or lower, but I think 600 ohm line would require a bit better transformation ratio. It will work, but the balun is going to get really hot. Most of those ready made baluns are going to get hot anyway even if they are rated at 1kV or 2kV. A lot of RF current is going to get force back into the balun.

You might consider building your own.

I think it's my turn this week.

In a typical installation which uses balanced line to facilitate multibanding a doublet the surge impedance of the balanced line is not critical.

The only time the 4:1 ratio needs to be 4 times 50 ohms is when the balanced line is terminated with a resistive impedance numerically close to the line's impedance.

Plenty of ferrite core baluns are in service working without losing large amounts of power. Mine is one of these.
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« Reply #3 on: December 18, 2009, 12:08:58 AM »

I think it's my turn this week.

In a typical installation which uses balanced line to facilitate multibanding a doublet the surge impedance of the balanced line is not critical.

The only time the 4:1 ratio needs to be 4 times 50 ohms is when the balanced line is terminated with a resistive impedance numerically close to the line's impedance.

Plenty of ferrite core baluns are in service working without losing large amounts of power. Mine is one of these.

Legal limit AM.

How can you say 4:1 is the best ratio when you don't know my specific situation??? ?

How much power are you running into your antenna with the ferrite core balun? A heavy 4:1 toroid wound voltage balun will work best for high power continuous carrier operation.

I've run 300 to 500 continuous AM watts into those other ready made type baluns in the past and they superheat if you try and run the antenna on all bands. They wont hold up. They are ok for intermittent SSB operation as long as you’re not running a high power legal limit linear.



Legal limit AM. I use ssb for testing purposes only.

How can you say 4:1 is the best ratio when you don't know my specific situation??? ?
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The Slab Bacon
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« Reply #4 on: December 18, 2009, 09:13:56 AM »

in all of my trials and tribulations trying to get short antennas to play well on the lower bands (for which I succeeded) I did a lot of experimenting with winding and testing baluns. Here is what I found:

All of the 1:1s are somewhat, if not totally impedance specific. The 4:1s were not impedance specific. When I swept them, whatever was on the output side showed up 4:1 to the input side, no matter what the impedance was. The 1:1s would do some strange stuff when you got away from the charactoristic impedance.

also the 4:1 added no noticable reactive component to the mix, where the 1:1 did when you strayed from the basic 50 ohms.

Just something to ponder.................as I know it is not heresay because I saw it with my own eyes! ! !

                                                    the Slab Bacon
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flintstone mop
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« Reply #5 on: December 18, 2009, 10:17:47 AM »

The max power allowed on a reciprocal license is 100W. I'm going to take a TS 50 and a radio friendly switching PS and a small tuner. The antenna will be 125 feet long and I thought that it would be less hassle and less weight on the bamboo support to use either HRO's favorite window line or ladder line and a balun near the tuner to get to 50 ohms.
I didn't want to hang the traditional "balun" at the top and deal with the finniky coax for multiband operation. I want to  monitor 80 and 160 to get an idea of the amount of QRM and N over there on the lower bands.
I'll mainly use 40M and 20M. A lot of DX on 20M during the daytime.
I might try to break some ice using A.M., but it's not popular over there in the Philippines. Everyone worries about the cost of operating high power radio over there. Even though they are allowed 2KW OUT. Nothing talks about P.E.P.!!!!!

Fred
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Fred KC4MOP
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« Reply #6 on: December 18, 2009, 11:01:34 AM »


The issue is power rating and how hot they will get. A 1:1 will get hotter than a 4:1 to couple ladder line to coax.



A 125' centerfed doublet is fed with 110' of homebrew open wire line. A balun is needed at the shack end.

Which balun will work better on 75 meters?
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KD6VXI
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« Reply #7 on: December 18, 2009, 11:19:30 AM »

A business class seat is over 4k right now because its Christmas and I can’t fly coach. Sometimes being 6'5" tall has its disadvantages.

One of my best friends / previous employer has a wife and 2 kids on the plane this morning to somewhere on the island.  Didn't realize we had this much traffic over to their at the holidays.

At 6'4", I can relate.  Best thing I've found is to sit in an aisle seat, and give the STEWARDESS' dirty looks when they come close to you...  Eventually, they will wait for you to move.

Of course, that's when I can't talk the client / boss into 1st or business class.  Needless to say, I sit in aisle seats a lot.

--Shane
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W2XR
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« Reply #8 on: December 18, 2009, 11:35:06 AM »

If high power or balun heating/losses are an issue, I suggest you consider the high quality, high power baluns available from Array Solutions in Texas:

"Model AS-200-T 4:1 Impedance Ratio. 1.5 - 30 MHz. Rated at 5 KW CW. CCS Heavy Duty windings heavy cores, Ideal for dipoles, or other antennas where a tuner is used to match the transmitter over a wide range of impedances.  For instance the multi band verticals or a Zepp fed with ladder line."

I use the 50 ohm/1:1 impedance ratio variant of this balun at the input to my homebrew balanced-L antenna tuner. Rated at 5 KW CW, it works great, with zero perceptable temperature rise at room ambient, running full strap plate modulated AM.

I would recommend these baluns to anyone who does not want to wind their own.

73,

Bruce
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« Reply #9 on: December 18, 2009, 11:40:44 AM »


A 125' centerfed doublet is fed with 110' of homebrew open wire line. A balun is needed at the shack end.

Which balun will work better on 75 meters?


I'd still use a 4:1. Since his ladder line will be acting as part of the antenna it would be better for all band operation. Those ready made baluns will throw common mode on the feedline anyway.

A 1:1 current balun should only be used for coupling coax feedline right to the antenna.

Well, that's my two cents worth on this subject.

73's

The antenna in question presents a 50 ohm balanced load at 3.9 mhz when installed next to my home.

This answer shows that you need to grasp the concept of impedance transformation in feedline which is not terminated in it's surge impedance.

The impedance of the feedline [here] isn't what needs to be matched to transfer maximum power to the antenna system.

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K1JJ
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« Reply #10 on: December 18, 2009, 11:40:44 AM »

Fred,

If you MUST use a 4:1 balun, make it for a single optimized band - out of coax, not toroids.  It will be immune to lightning and saturation - and I feel generally better suited for the purpose.  For single band operation, just connect it across the openwire and slide it up and down the line until you find the 50 ohm 1:1 match. I sometimes use a shorting wire 5-10' behind it (on the openwire) to reference it to a particular impedance for 75M.  

Multiband: That said, I could never justify using any type of 4:1 balun for multiband use on openwire to coax and a tuner.. that's just axing for trouble and losses on some bands. For multiband use, just run the openwire to the shack DIRECTLY to a link coupled (or equiv) antenna tuner AT ALL COSTS - no coax or baluns.


The first three paragraphs describe how to make a 4:1 coaxial balun for a single band:

http://amfone.net/index.php?pid=12

T
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K8WBL
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« Reply #11 on: December 18, 2009, 12:10:27 PM »

Hello Fred, what I use is 148 foot center fed Zepp, with 90 feet of 450 ohm ladder line connected to a coax balun wound on a 4 inch PVC pipe.  It resonates really well at 3.885 Mhz and also on 7.2 Mhz.  It is called a Half Extended Double Zepp.  I have a DPDT switch just before the balun to switch it over to a tuner, in case I want to run it on other freqs.  Otherwise it stays attached to my Globe King 400B.

73, Tim K8WBL
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« Reply #12 on: December 18, 2009, 12:18:43 PM »


This answer shows that you need to grasp the concept of impedance transformation in feedline which is not terminated in it's surge impedance.


Well, I said I was through on this subject, but forget that !

He said he was going to run his antenna primarily on 20 and 40 meters so a 4:1 balun would be best even if he was going to run it on 75 meters too for that reason.

The other suggestion of making a 4:1 balun out of coax is a good idea too, but unless he has a built in 4:1 balun inside of his antenna tuner you don’t want to just directly connect the ladder line to the tuner’s SO239 connector. I don’t think he was referring to using a link coupled tuner, he said a “small” tuner.

P.S. You might want to read and understand what the person was saying and asking before telling people that they don’t know what they are talking about.

That enough of that subject stuff is great but we have lots of people reading here who deserve to see things which are correct.

I asked you a specific question with specific parameters. The question is answered easily when understanding of impedance transformation is understood. You answered it incorrectly. Use this as a learning experience. Everyone makes mistakes. No dancing necessary.

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flintstone mop
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« Reply #13 on: December 18, 2009, 12:25:56 PM »

Hi Everyone
I'll quote Tom,
Multiband: That said, I could never justify using any type of 4:1 balun for multiband use on openwire to coax and a tuner.. that's just axing for trouble. For multiband use, just run the openwire to the shack directly to the tuner at all costs.

I'm just using a small 300 watt tuner. It doesn't have provisions for balanced line with a built in toroid. It's just for coax only. I have used the commercial 4:1's and YES on the lower bands and A.M. 300W carrier it gets plenty HOT, but I will be listening on 160 and 80 and operating on 20 and 40, and I thought that the 4:1 balun would be easier and ladder line be a lighter feedline than coax.

This subject about feedlines and baluns pushes a lot of buttons......
I might be better to get one of those BuddiSticks. Those work pretty nice for a portable antenna. Just have to raise it off the ground and its radials. Some ty-wraps and a 10 foot piece of bamboo and a little circle of raised radials should be good.

Thanks for the info a lot to always be learned here.

Fred
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Fred KC4MOP
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« Reply #14 on: December 18, 2009, 12:41:31 PM »

<snip> Multiband: That said, I could never justify using any type of 4:1 balun for multiband use on openwire to coax and a tuner.. that's just axing for trouble.
<snip>


Why? ? ? ? I do it all of the time at big power levels and short antennas and never have any problems  Huh  Huh

Of course, I designed and built the balun myself to take the punishment.
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K1JJ
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« Reply #15 on: December 18, 2009, 01:23:29 PM »

Hi Frank,

I'm curious ... I'm sure you have a good reason, but why use a FIXED 4:1 balun for multiband use in the first place when the input impedance (and ratio) swings all over the place on the various bands? A 4:1 ratio is good for only one specific band/freq, right?   A balanced, series or parallel configured variable link coupled tuner interfaced directly to the openwire will accomodate any impedance ratio... 1:1, 2:1, 4:1, 10:1, etc.    If bringing the openwire into the shack is a problem, then use the inner conductors of two coaxes with their shields tied together as the "openwire" run thru the wall.


For those who have the room - and to complete the dream...  To have a multiband antenna that will be within 5db of a Yagi in forward gain and maintain a desireable figure-8 on all bands 160-10M ---  Put up TWO antennas as flat, straight and high as possible: A 180' flat top for 160-40M and a 22' flat top for 10-20M each fed with openwire - and use two separate link coupled antenna tuners directly fed with the openwire.  No better system for all around low-loss multiband use.  Nice patterns with no big broadside null surprises.

Build one or two of these simple tuners and your balun and antenna pattern problems are over:   Grin

http://amfone.net/Amforum/index.php?topic=18054.0


T





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« Reply #16 on: December 18, 2009, 02:18:50 PM »


I asked you a specific question with specific parameters. The question is answered easily when understanding of impedance transformation is understood. You answered it incorrectly. Use this as a learning experience. Everyone makes mistakes. No dancing necessary.


Dude, I'm going to be the better person here because it’s totally obvious you are trying to goat me into getting mad. My answer was in response to what he was using and to your question combined. It was NOT a direct answer to your question about using it on 75 meters only.

I've had way too many years on experience working on antennas with coax, baulns, etc., etc., etc., and I know what works and what doesn't. I could care less about what the total Z is of the antenna at the transmitter’s output with the ladder line on 75 meters only, it will be different on the other bands and that’s what matters.

I made no mistakes..


STOP trying to make this a personal issue. Stay focused.

It's obvious you have experience. That's not the issue. Answering questions based entirely on what you have seen is going to lead to wrong answers.

Experience is great but it makes some people overconfident.

4:1 baluns are usually worse for power transfer when used following a T match into balanced line and a doublet. They are only better than a 1:1 when the impedance presented in the shack is relatively high.

Model or guestimate Fredd's antenna's impedance on different bands based on experience. Use a feedline transformation calculator with a typical feedline length or Fredd's spec. Look at the impedance presented to the load in the shack. Do you still want to divide it by four???
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« Reply #17 on: December 18, 2009, 03:41:32 PM »

One lesson I have learned on this board to avoid controversy, never talk about religion, sex, politics and baluns.
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W1GFH
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« Reply #18 on: December 18, 2009, 03:53:28 PM »

I'll bite. What exactly is the average loss of power in watts in a balun-coupled feedline vs a link coupled feedline?
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« Reply #19 on: December 18, 2009, 04:42:15 PM »

I'll bite. What exactly is the average loss of power in watts in a balun-coupled feedline vs a link coupled feedline?

That question cannot be answered.

It's like asking to quantify the blueness of the sky.

You need specific information to even start.

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« Reply #20 on: December 18, 2009, 11:10:23 PM »

....
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AMI#1684
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« Reply #21 on: December 20, 2009, 01:11:48 PM »

Opps is right  Grin

What was overlooked was the fact that all of those ready made baluns, both 1:1 and 4:1, will leave common mode of the ladder line unless you build one yourself using two separate windings. That in itself changes everything and using normal calculations to obtain the source Z of the antenna system with a tuned feeder will be thrown out the window.

It's the reason why all of the modern "T" network antenna tuners that have output terminals for balanced line have a 4:1 toroid balun inside and not a 1:1.

Anyway, you just can’t argue with some people, it’s not worth it.

Where do you come up with this stuff?

The real reason 4:1 is used in ham T matches is the ability to tune low SWR impedance range for a given set of tuner parts is larger. I need an editor.

Unfortunately the losses are  higher than a 1:1 in a lot of cases. Happy appliance ops will never know the difference though.

Common mode is not a problem in real life typical setups.

I have homebrew and commercial 1:1 baluns in service at several installations. They all work fine when you use them within their limitations. The commercial toroid units do much better over a wide freq range.
 
Realize the antenna coupler needs to match the impedance presented by the antenna system including the transformation taking place in the feedline and not the impedance of the balanced line itself.

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« Reply #22 on: December 20, 2009, 01:40:20 PM »

a modern t section tuner  is sold to people who don't know any better. The balun is added to make them feel better about getting ripped off. The added feature that they are usually high pass networks makes it even more funny.

50 feet of 1/4 inch tubing, a couple feet of PVC pipe and a couple flea market caps. Maybe $100 to build a tuner.....Oh yea the added price of a hunk of plywood
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« Reply #23 on: December 20, 2009, 08:17:12 PM »

I wish I had some common mode, maybe I would look better and be smarter.
Santa please bring me some common mode.
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« Reply #24 on: December 20, 2009, 08:33:20 PM »

Where do you come up with this stuff?

The real reason 4:1 is used in ham T matches is the ability to tune low SWR impedance range for a given set of tuner parts is larger. I need an editor.

Unfortunately the losses are  higher than a 1:1 in a lot of cases. Happy appliance ops will never know the difference though.

Common mode is not a problem in real life typical setups.

I have homebrew and commercial 1:1 baluns in service at several installations. They all work fine when you use them within their limitations. The commercial toroid units do much better over a wide freq range.
 
Realize the antenna coupler needs to match the impedance presented by the antenna system including the transformation taking place in the feedline and not the impedance of the balanced line itself.

Using a "T" network tuner period will create losses, mainly on 75 and 160 meters even with a 50-ohm antenna system and no balun. "T" network tuners do in fact stink, but nevertheless, connecting the typical 300 to 450 ohm ladder line to a "T" tuner will require a 4:1 balun so the tuner will adequately tune on all bands. You don’t want to use a 1:1 bauln with the "T" tuner on all bands using ladder line. The tuner's components are going to get hot as a result.

Common mode may not be a problem in real life typical setups, 90% of all modern HAMs and CBer's have it because unbalanced coax use is the norm. However, it will affect the use of balanced feedline. Your antenna systems Z without common mode will be different with it.

Please tell me of an impedance/frequency where a 1:1 balun on the output of a T match tuner will make the components in said tuner run hotter than a 4:1.

My antenna system has negligible common mode energy on the feedline. Just like many others. It isn't that hard to accomplish.  
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