Balun help

[KD6VXI]

1) With openwire, you will find yourself "rowing" around the bands. Every time you move, whether it be up the band or (heaven forbid) changes bands, it takes some moved jumpers and tuning. This is in addition to tuning the exciter and amplifiers.  Some people don't mind a bit - others feel it's just more psychological resistance to changing bands.

Using coax fed antennas, it's a quick turn of the coax switch and you're there.

What would you do in the case, for example, if you worked a  lot of AM at 3870-90, but you were also an avid CW DX'er at 3500-3520? 

Put up a cage dipole or a double dipole.

--Shane

[Detroit47]

Hi Gentlemen
I am overwhelmed by the response to my question. I would like to thank all who contributed. I should point out that I am on a postage stamp lot. The lot is a typical city lot 50 x 150. There is a large maple tree in the front yard. I was going to use it for one end of the dipole. In the back of the yard I have a wooden mast about 30 feet high. There is about 135 feet between these two tie points. Unfortunately I have no center support available for the wire. So I am concerned about hanging a coil of coax at the feed point. Would sag be an issue? I have seen ads for copper weld wire I believe it has a steel core to prevent sag.  I have plenty of plain copper wire on hand I will buy whatever will work the best. An open wire feed line is not an option due to my station location and ice. All of my rigs are of the tube variety Collins and Johnson. I didn't know if that would matter but now you know. I have plenty of ½ in hardline on hand for feed or 9913.
73 Johnathan N8QPC

[K1JJ]

Hi Johnathan,

Thanks for the description of your QTH.

Well, based on the dipole not being supported in the middle, (with ice loads) I would look to use some lighter RG8-X? coax (first choice) or even some lighter RG-58/59U type for a 75M coax fed dipole. I take it you will be running about 150w carrier, so that lighter coax will be fine on 75M. 

For the balun, you could always slip some light ferrite beads over the coax at the feedpoint, or go without a balun. Keep the feedline at right angles all the way to the ground if possible. At 30' high, you have less than 1/8 wavelength of straight coax run, so no sharp angles near the antenna.  Check sources to see what the best type of ferrite beads are for 75M use. The permability and inside diameter to fit snuggly over the coax is what you want to know. You could always bury that hardline from the shack to the dipole and join it to the coax underneath the dipole.  Use 18" long PVC pipe standing up in the ground as a protective junction.

 Even though solid copper wire will work,  I'd use Copperweld wire for a 135' span.    #12 is a good choice. The other pure copper stuff may stretch and eventually break under wind and ice loads if unsupported in the center. Be careful not to poke your eye out when working with Copperweld. It's like a steel spring. Also, do not kink it or it will rust thru quickly at the fracture point. (copper coated steel wire) 

Some of us use aircraft steel cable in each tree limb as the end supports. Rope will last only a year or two due to wind/friction.  You may also consider pulleys that move with a weight up and down in the wind at each end. Make sure the rope is durable so the pulleys don't eat thru them.

Get the dipole as flat, straight and high as possible. A little sag in the middle is OK.

I'm sure the guys will have more suggestions for you. The main idea is to get the antenna up high, flat and away from house wiring, plumbing and street power lines to give it a chance to perform.


Good luck.

Tom, K1JJ

[k4kyv]

Another possibility, if the stuff is still available, would be 72-ohm transmitting twin lead.  It would make a balanced feedline from the dipole, and the loss/ft is probably comparable to that of coax.  Then you could run 72 ohm coax from the transmitter to the twin lead, and if need be, insert a balun where the two lines are connected together.

I remember seeing it sometime in the 70's.  It looks like heavy duty zip cord, and the conductors are stranded, about #12, but the insulation is the same kind of brown plastic that is used on other types of ribbon  line.

I started out using 72-ohm TV receiving twin lead.  It would crap out at about 300 watts on cw.  I used it for a couple of years @ 100 watts input on AM.

Before the advent of coax, "twisted pair" was often used before WW2, for those who didn't want to use open wire.  It consisted of two pieces of rubber covered copper wire, I assume ordinary single conductor a.c. house wire, twisted together using a hand drill. No doubt, pretty lossy.

I have seen descriptions of a "fan dipole", with several wires on each leg, all connected together to a common point at the central feed point, but fanned out to a  distance of 3 or 4 ft. at each end.  It supposedly is broadbanded enough to work across 80-75m.  You could probably make it even broader by using slightly different lengths for each of the wires. Similarly, cage dipoles were popular a few years ago.

The single open-wire fed dipole is practical for my setup, since I have one tall support system for the dipole, and multiple dipoles or even a single multi-wire  dipole would be difficult to erect so that it would stay up.

[ka3zlr]

Well,...I look at it this way, I don't know what type antenna coupler Johnathan has, he does say he's using mostly Hollow State rigs..that's a plus...So I'm figuring he'll have to pick a spot and cut for resonance.. and stay close....

Don't sweat the balun...Build a simple dipole get it up high as you can.. any issues... RFI Proof the inputs of the rigs...Ground everything... Simple... Then Build a Decent Coupler...so he can move around... one benefit to Hollow state..easier to RFI proof...

73
jack.
 

[WA1GFZ]

With the coax hanging in the near field I wonder how effective a balun really is at the feed point. I would think it more effective near the ground or feed point. Without a center support that is a lot of extra weight causing sag.

[The Slab Bacon]

Hi Gentlemen
I am overwhelmed by the response to my question. I would like to thank all who contributed. I should point out that I am on a postage stamp lot. The lot is a typical city lot 50 x 150. There is a large maple tree in the front yard. I was going to use it for one end of the dipole. In the back of the yard I have a wooden mast about 30 feet high. There is about 135 feet between these two tie points. Unfortunately I have no center support available for the wire. So I am concerned about hanging a coil of coax at the feed point. Would sag be an issue? I have seen ads for copper weld wire I believe it has a steel core to prevent sag.  I have plenty of plain copper wire on hand I will buy whatever will work the best. An open wire feed line is not an option due to my station location and ice. All of my rigs are of the tube variety Collins and Johnson. I didn't know if that would matter but now you know. I have plenty of ½ in hardline on hand for feed or 9913.
73 Johnathan N8QPC

Jonathan,
              I live on a similar sized suburban lot. (50 x 145) with the house pretty much in the middle of the lot. All of my antenners have to go behind the house as not to be too conspicuous to the neighbors. This leaves me about 70' of horizontal run to put up any kind of wire antenner. Try this antenner design (see attached drawing) With the right tuna it will work from 10-160, and puts out a strapping signal on 75 & 40. Many here have both heard and/or seen it. It works FB!!

                                                                The Slab Bacon

[K4TAX]

I have to agree with Don, K4KYV, on this one.  A balanced antenna is the better way to go.  Put up the longest wire you can, feed it in the center, connect it to a well designed tuner and enjoy ham radio on all bands. 

For what it's worth, handling open wire or balanced feed line is much easier than most folks understand.  Correctly installed it will last for years, handle all the power you can generate and provide the lowest loss of any transmission system.  If it is truly balanced, there will be NO RF in the shack and actually no ground is needed other than for lightning protection.

As to a tuner, a truly balanced tuner will work great.  I don't favor using one of those with the internal 4:1 balun.  Usually they are over rated and don't work well with a high reactive load.  A 1:1 current balun rated at 5KW or so will always be better.  Hence, my suggestion of a coax balun. 

Been using the above methods very successfully for nearly 50 years.

73
Bob, K4TAX

[K1JJ]

After reading the latest comments and thinking more about it, yes, openwire might be a better solution for Johnathan's situation.

Johnathan, you mentioned you cannot use openwire, but maybe take a look at the more low-profile stuff.  It will not stand out much more than coax and you can always slip it thru a window for now.  This will give you all bands to have fun with using a single antenna, as Bob said.  You could easily build an antenna tuner for it.

Otherwise, the coax fed dipole will suffice as well for 75M only.

You have many options now to look into.

Good luck..

Tom, K1JJ

[K3ZS]

My lot is full of pine trees, so I had only one place to put up a 135 ft doublet.   I feed it with about 150 ft of the "brown crap", 390 ohm (called 450 ohm window line) twin lead.    I am using a common T-tuner, but as mentioned here, the baluns in these are usually inadequate.    I am using a high power-rated ferrite current balun about 10 ft from the tuner.    With the suggestion of K1JJ, I added a 2nd 16 ft dipole to the 135 ft, separated with some 6 inch PVC pipe sections.    As my favorite bands are 80, 40 and 10M, this antenna combination works great.   It also can be tuned on the other bands as well.   The I made a chart using MS Word, of the tuning settings for all bands and within the bands.    Band changing is simple when using the chart and requires only a little tweaking if you need a perfect match.   The only caveat is that during heavy rain, and icing, your chart will be way off and require more adjustment of the tuner.    It is the general opinion of many on this board that only a true balanced tuner and true ladder line are the only options, but I find my simpler solution is just about as effective in actual operation.

[Ed/KB1HYS]

They say if you want to get a bunch of Amatures worked up, ask an antenna question!!

I'm on a small city lot too. Similar problems, although Ma-nature helped me with some big trees. I also try to keep the antenna somewhat stealthy. (Minimizes TVI/RFI issues that way)  .

If your power level is going to stay low (~150watts or less), you can homebrew some very lightweight ladder line using insulated wire or even use the TV-Twin lead. I've been using that here on my "All bander" and it does work fine. No problems with ice/weather damaging it (yet). 
Don't sweat a bit of sag in the middle, slight changes in feed point impedance and pattern will be insignificant compared to the effect of the height.  Trying to keep the flat top perfectly flat can put a LOT of stress on the end supports.

If you have to use coax, I'd try a fan dipole. (multiple elements on different freqs).  You can use a tunna to minimize the antenna cut and try period too.

If you can swing a good ground, mabe an inverted L?? Run the hardline to the base of one support and up-n-over to the other?

If you can go round the lot, how about a loop (cloud burner)? 

Anyway, lots of good advice on this board.  Just remember that EVERY antenna installation is a compromize based on the surrounding circumstances.

[k4kyv]

I have to agree with Don, K4KYV, on this one.  A balanced antenna is the better way to go.  Put up the longest wire you can, feed it in the center, connect it to a well designed tuner and enjoy ham radio on all bands... 

Hey Bob,

I haven't heard you on the air in a long time.  I worked Derb (N3DRB) last night and we were talking about that transmitter he came down and picked up from you.  He stopped by here for a visit first, and took a bunch of photos of this station.

[WD8BIL]

Dog piling is not useful.

Then why was only ONE dog removed from the pile?

[ka3zlr]

They say if you want to get a bunch of Amatures worked up, ask an antenna question!!

LOL..Good One Ed...it's the Truth...

[Detroit47]

Hi
I'm back I have been looking over what was suggested here. The suggestion of the folded dipole by The Slab Bacon was a good one. I was looking into the Barker and Williamson stuff at one time. As I can see they are not a true folded dipole but a terminated variety. I am going to show my ignorance and ask how to bring ladder line in the house. Will it radiate if it is close to furnace ducts wires etc.? I have a Johnson 500 and a Desk Kilowatt that I would like to be able to use. Several of the local Hams are using the G5RV design and are praising it. Any thoughts on it? The more I read about ladder line the better it sounds. How big of ladder line does it have to be?  If I ran the ladder line to a balun and switched to 75 ohm coax would this work out. I have some of the 75 ohm cable hard-line available. I am referring to what Don; K4KYV was talking about with the brown stuff. I was thinking of putting it inside of plastic conduit in the house.  I went to school for electronic engineering but am an antenna moron.
Thanks to all who contribute 73 Johnathan N8QPC

[WB2YGF]

I like my G5RV, but I hear AM'ers making fun of those who use them, so if you do, you might not want to admit it. 

[WB3JOK]

how to bring ladder line in the house. Will it radiate if it is close to furnace ducts wires etc.?

Yes, there is a field around the wires that is not contained (unlike coax, which has a shield).

I believe the rule of thumb is to space the ladderline away from any conductive objects by at least four times the spacing between the wires... so you can't just run it inside a PVC conduit and have it close to ducts and house wiring...

[Steve - WB3HUZ]

The brown stuff is spaced about 1 inch. So if you keep it 2-4 inches from metal, you're good to go. By metal I mean large stuff or for long lengths of the ladder line. Running near a nail or two in your floor joists or similar isn't going to hurt anything.

The G5RV is as good as any other center-fed antenna at the same height, in most cases. Where problems occur is the transistion from the ladder line to coax. Some manufacturers provide a crummy balun and/or loss coax. This can reduce the performace of the G5RV on some bands, most notably 80 meters. Excellent info on the G5RGV here.

http://www.vk1od.net/G5RV/index.htm

I would skip the balun and coax part and run the ladder line straight to the tuner. You can also play off the length of the wires in the flat-top portion (something other than 102 feet) and the feedline length to the point where you may not even need a tuner. Check this link.


http://www.w5dxp.com/notuner.htm

[The Slab Bacon]

I like my G5RV, but I hear AM'ers making fun of those who use them, so if you do, you might not want to admit it. 

Yep!! G5RVs suck!! Just about anything else works better! Vortex Joe (N3IBX) had one along with a standard 120' dipole. the difference in signal was beyond substantial! I kept threatening do drive up there, tie it to the back of my truck and pull it down!

IIRC, with a G5RV part of the feedline is SUPPOSED to radiate as a vertical radiator on certain bands.

Jonathan,
           If you do not have room for a resonant length antenna, put up as much wire as you can, feed it with balanced line and a good tuna and it WILL work. Itz just that simple.
I have the same problem as you with feedline and metal obstructions, here is how I did it.

First of all I built a STRAPPING "t" type tuna. (the cabinet is the size of an R-390) Then I ran a short (about 9') of high grade RG-8u coax fron the tuna to the back wall of the basement. I then built a STRAPPING 4:1 balun and mounted it to the back wall and ran laddah line out to the antenner.

Using a 4:1 balun keeps the impedance of the short coax VERY LOW, thus minimizing the losses of running it (the coax) at through the roof high swr to just about nill. I have been using this antenna and feeder setup for years behind a homebrew 4-1000a transmitter without any problems and no one has complained about me having a piss weak signal!!

Keep in mind that coax becomes very lossy when feeding a high impedance (long) antenna due to the capacitive reactance built into it, but when you sin the other way and run it at a very low impedance, all you really have to worry about is the I-R losses.

Where there is a will, there is always a way!! Sometimes you just have to look "outside the box" to find it!

                                                                   the Slab Bacon

[W3SLK]

I don't know how big your lot is but a loop supported at least 4 points makes a dandy radiator and you can use coax. I'm not sure what climate you're in but it is certainly quite on hi-wind/low humidity days when static build up is an issue. I would put up another one but I would need about 2 miles worth of wire to fit the lot

[flintstone mop]

Johnathan,
This group of radio folks really aren't that bad. Welcome to AMFOME.
During my small lot days a non-resonant dipole and open ladder line was the best. Steve, WB3HUZ helped me find the right trees to get a real nice 180 foot long dipole up about 90 feet in the air. My lot had some real nice tall, strong oak trees.

Even 30 feet high is an ok radiator for most of the bands. Stay away from the B&W antennas. There was one model that was nothing but a dummy load in the center and about 100 feet of wire on each side. You can always hang the ends of the dipole down at the ends to make up the length needed for a particular band.

What bands are you interested in?
I know this is perfect antenna wx right now for us folks in the deep freeze.

Fred

[K3ZS]

I have vinyl windows in my house.    I keep the half-screen in the top half of the window.    I run the brown crap window line under the window and shut the window down on it.     There is enough weather stripping to make a good seal, just use the same spot all of the time.    On the outside, I weaved a 1 ft length of fiber glass rod between the openings of the window line.   This keeps it extended to it doesn't fall down on the outside aluminum covered window box.   I support the twin lead about halfway to the antenna by running it through a plastic plumbing connector, this is tied up to a tree using military dacron rope.  This keeps the antenna from sagging and brings the feedline away at right angles. It is also supported at the house not far from the window.   You can use rope and feed it through several openings of the window line to spread out the strain on it.  The antenna is not supported in the middle and I am using about 150 ft of feedline.    The antenna, a 135 ft doublet, is supported using 3/8 inch double braided dacron (Radioworks and other antenna suppliers have it).    The dacron resists breakdown from the sun's UV rays.    Nylon won't last long.    One side is run through a pulley and counter balanced with 1/2 of a cinder block.    That way blowing trees and ice on the antenna won't break it.    This has been up for 10 years, had to replace the antenna wire once when it was vaporized by a direct lightning strike.    I used to ground the antenna before that, I now just disconnect it.    The dacron rope is the orginal, the only problem is that the birds and squirrels like to chew on the loose ends,  where the excess is coiled up.

You can run a short section of coax through the wall and put a hefty, weather proof balun on the outside instead of running the twinlead inside.    Check out the DX Engineering web site for baluns.

[WA1GFZ]

Frank's antenna with open wire line into the shack to a tuner would be more efficient eliminating the balun and coax between the tuner and antenna. Less stuff to have loss. Adding a load like the B&W will make it easier to match but also make heat which is antistrappessant

[K1JJ]

Frank's antenna with open wire line into the shack to a tuner would be more efficient eliminating the balun and coax between the tuner and antenna. Less stuff to have loss.

At 60' total length, (not including the folded legs) Frank's system is certainly a clever method of linear loading to get a shortened dipole to work well on 75M and 160M. Great method.


But since Johnathan has a generous 135' of support space to work with, and is concerned with light weight to keep the sag at a minimum, (no center support) would a single wire 135' full size dipole fed with lightweight openwire be a more suitable choice for his conditions?

T

[Tom WA3KLR]

I did a rather extensive study of Frank's antenna system 2 years ago and recommended moving the balun from the output of the tuner to the input for less loss as I recall.  The study included other incremental changes and their losses, which order to procede, all by antenna and transmission line simulations:

http://amfone.net/Amforum/index.php?topic=9181.0