The AM Forum

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

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! 

C 

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. 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??? ?

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

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

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?

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

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

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.

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

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

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.

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

<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  ???  ???

Of course, I designed and built the balun myself to take the punishment.

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:   ;D

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


T

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???

One lesson I have learned on this board to avoid controversy, never talk about religion, sex, politics and baluns.

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.

....

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.

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

I wish I had some common mode, maybe I would look better and be smarter.
Santa please bring me some common mode.

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.  

Dave, I think your problem is you have too much common sense and not enough common mode.
Want me add your name to my letter to Santa?

Will Santa send me a 1099 form along with any gift?

The DX Engineering web site recommends using a 1:1 current balun as an add-on to an unbalanced tuner.  The reason is that by chance the impedance could just as much be much lower that 50 ohms at the end of the feedline than higher.   In that case the 4:1 makes it even lower.   If you know that your impedances are always going to be higher then the 4:1 is the better choice.    Seems to me if you have to make a choice it would be better to calculate or measure your actual impedance at all the bands you want to use.   The same would go for link coupled tuners, whether to use series or parallel tuning.

You would have to imagine this because that's not what exists with balanced line.

Soooo you think the common mode current on a balanced feedline depends on resonance somewhere??

WOW

My last post I assumed this was with balanced ladder or window line.    I found out the hard way that the balun built into my MFJ just was not providing a very good balance on 40 and 80 meters.   On 160 it might as well not been there at all.    I salvaged the situation by getting an external high power balun.    I plan on building something like the K1JJ tuner for 160-40.   Will be curious to compare that with what I have now.

You will have a real tuner if you build one then you can sell the toy on epay

The MFJ baluns are tiny, barely adequate for 100w SSB. Well atleast mine was.  It got baked when i was running my Valiant.

A good link-coupled tuner is easy to build, costs a lot less per watt of power handling (compared to commercial products) and will be able to tune just about anything from the gutter & Down spout to a Multiband OW fed Dipole - no balun required.

A link coupled tuner used this way IS a balun.

yes very true Dave. And a T tuner is an UN-UN

Funny, but I guess that's right.  I never looked at it that way, I only looked at it as an impedance transformer, not as an unbalance to balanced transformer as well, which it is...

Well I'll be...

As a result of this (rather long and interesting) discussion I have taken a sledge hammer to any 4:1 baluns in my possession, pummeled them to dust, and scattered the remains among unmarked graves. :D

Actually, I confess, I operated a 4:1 balun and a T-tuner with a multiband nonresonant dipole for years. I enjoyed lots of terrific QSO's with stations all over the world and didn't even know I was doing the wrong thing...

Chances are you were only doing the wrong thing 1/3rd of the time.

This 4:1 balun has served me very well for many years! ! !

OK Frank ....wecome back home.
That was the balun you made? Very nice and big ball#.
Could you pls PM me and give a list of material....the mixture for the Ferrite and the number of turns. I can hopefully make out from the pic what goes where. I gotta make a copy of that for future uses.
Phred

What led me to find out the lousy balance of the MFJ tuner balun was the noise pickup from all the noise and crap generators in my house.   At one time, being a cheapskate, I was using and end-fed wire with an L tuner.    I set up a temporary 40M coax fed dipole about 50 feet from the house.   The noise from the house was greatly reduced.     I then set up a 130 ft doublet about 150 feet from the house, fed with #14 window line.    I got an MFJ T-tuner to use with it.    I found out that the noise was about as bad as with the end fed wire.     I tried an external, but low power voltage balun and found the noise pickup went away on all bands.   I confirmed the crappy inbalance with a scope and a pair of matched 100 ohm resistors to ground.  I then purchased a high power rated 4:1 current balun from DX Engineering rated for use with tuners with HV rated insulation.    I have been perfectly happy with using it with the MFJ.    The balun stays cold when running with the linear amp on 80-10M.   I can only run barefoot on 160.    With the shortened antenna on 160, and everything tuned, I can run 100W carrier into the balun and don't notice any heating.    However, maybe I don't know what I have been missing so I will try a link coupled tuner and do some honest comparisons between the two systems to see if I see a difference.

http://www.hnsa.org/doc/radio/chap9.htm

I see your point about common mode voltage, but that's why you use a balanced line and a balanced input device, to cancel out common mode signals.    The isolation of link coupling presumably has other benefits as you have described.

Bull Pucky