The AM Forum

Hi Guys

I am going to put a 75 meter dipole at my station. I am looking for a little guidance on a 1 to 1 balum. I have heard about people having problems after they have been up for a while. Any recommendations on wire type or type of balun to use. And homemade versus store bought. I will be running legal limit.I don't want to put up some junk and have grief later. I'm confused and cold in Michigan.
73 Johnathan N8QPC

Hi Johnathan,

Welcome to the AM BB.

Here's an intro article about the various baluns you can use:
http://amfone.net/index.php?pid=12


For high power, using coax into a dipole on AM, use the easiest and most durable method:  Coil up about 6-8 turns of coax from your feedline just at the dipole feedpoint -  make it a 4"-6" diameter, into a coil hank and tape it.  Hang it right at the feedpoint of the dipole. Hopefully you have a center support for the extra weight.

This will act like a choke and greatly reduce unbalanced RF currents on the outside braid - the usual cause of feedline radiation.

Don't bother with those W2AU type commercial ferrite baluns. The are known to smoke at QRO AM..

There are other methods as described in the article, like using ferrite beads slipped onto the coax. But the coiled coax or a combination of the two is about the best.

Be aware that you can simply coil the coax into a hank for 160-40M. But above 40M you should use a coil form, like 4"-6" PVC pipe, so that the turns are spread out to reduce inter-winding capacitance. Random coil turns touching each other would make the choke less effective on 10-20M.

Good luck.

Tom, K1JJ

You probably don't need one.  Just put up the dipole and see if it works FB. If it does and you have no "RF in the shack" problems you are good to go.

She's the Governor of Alaska

 

Cone om, Dom, you kmow he just has his m's amd n's comfused  ;D

I bow to you gentlemen in your greatness. I am not worthy to soil your boards, and waste your time I hope that I have entertained. Lastly I would like to thank K1JJ.
73 Johnathan N8QPC

Or he could use D-X grease to lubricate the antenna wire.

http://www.legendary66.com/americanicons/01/dx_gasoline.html

I'm justa a unun. Ain old enough fo no balum.

Jonathan said:

You have now been tried by fire ;) Welcome to the board Jonathan. The thing to worry about is when we treat you nice, then you know something is up! :D

Bob's "ugly balun" will do the job and handle about all the power you can generate.

See pix.  It is made on 3" PVC, has about 25 ft of RG-213 wound on it. 

73 Bob, K4TAX

Johnathan,

Here's a hands-on, easy-to-understand article that lays out the details.  It has specifics, measured data and reasons for using coiled coax baluns.

http://amfone.net/Amforum/index.php?topic=7694.msg55993#msg55993

Also, a search on this BB for "coax baluns"  will show some more threads.


BTW, when the guys here work ya over, that means they like ya... :-)


73,

Tom, K1JJ

I wasn't kidding or trying to be smart when I said you may not even need a balun. You can save yourself a lot of hassle by trying the antenna without one first. If it works OK, you're done. If not, then you can engage the balun action.

The reality is that if you can run your feedline away from the feedpoint at a right angle (essentially straight down) for 50-60 feet, you probably won't need a balun.

Steve's essentially right.
If you look at typical antenna patterns, height above effective ground, interference from power lines, trees, other antennae in the neighborhood including yours and all the other crud of modern civilization your typical amateur antenna setup may work fine without any balun.  Try that first.  I assume your using a 1/2 wave cut for the operating frequency and no other antenna tuner.

Do some reading or ask us some more questions but sometimes the RF in the shack can be cleaned up by just making the feed line shorter or longer.  Many of us use balanced feed through what you've known as 'twin lead' but beefier wire, etc., but that's another story.

 If you still get RF in the shack on your preferred band without a balun, then make up a compromise for 160, 80 and 40 meters, say 20 turns single layer on the 4 1/2 PVC as suggested.  If you can see much difference in the signals received or in what operators tell you on the other end, I'll be surprised.

Your in for a lot of fun just trying stuff. There's a lot of cookbook stuff out there but a lot of us tend to play with just about every combination over the years.

Yes, a simple dipole is probably one of the most forgiving antennas. As Steve says, if the feedline comes away at right angles, the balun requirement is greatly reduced, especially for 160M and 75M. This is because the normal height above ground is usually small (1/4 wavelength) and the pattern becomes a quasi-omni-directional  blob at many vertical angles.  Someone would be hard pressed to actually see a difference in pattern with or without a balun.

But when a dipole gets higher, like 1/2 wavelength or so, the pattern becomes sharper and more easily affected in the real whirl. There are 20-30 db nulls that can be wiped out by a little feedline radiation. (Assuming you want these nulls for an overall sharper broadside pattern with side rejection) It gets even more critical when feeding multiple array configurations where baluns are always needed to maintain equal phase between bays, etc.

Bottom line is, I doubt anyone has the capability to measure the PATTERN difference on 75M using a LOW dipole, with or without a balun. So the only criteria will be whether there is RF in the shack or not.

But, on the other hand, remember that unlike using openwire or twinlead which is balanced line, coax is an unbalanced situation into a balanced antenna. Might as well give coax the benefit of the disadvantage. To coil up 6 turns of coax into a hank is such a minor detail, I say do it for any dipole, 160-40M. Though, I admit in some cases, this may put you in the same category as the guy who follows his dog around the property with a pooper scooper... :-)

Pictured below: Here's a situation where I decided to use baluns.  Notice each homebrew 6M Yagi has it's own 4:1 coaxial balun transformation...   Gary looked up the tower and said he could imagine someone falling down the tower and bouncing back and forth like a pin ball... :-)

T

That's what I've been using for the last 25 years and although it seems to be OK with my mere 100 Watts out, I'm worried about putting 300 Watts carrier on it.  The 40 M traps have developed radial hair line cracks in them but they still seem to be working OK.  Looks like I have some fireworks in the making when I go QRO.

Al VTP

I've used coiled up coax on PVC forms for  years.  Works great, no problems with saturation.

Want multi-octave, use multiple forms at rt angles.  3, 4 and 6 inch work great for a 1.6 to 6 meter balun, IME.

--Shane

If you really need a balun, I prefer the ones made by DX Engineering.    They will handle AM duty cycles and power with good balance.    Their web site has some good info on baluns.   Disclosure: I have no financial interest in this company.

Absolutely the best bal-un in the world for a dipole antenna is balanced, link-coupled antenna tuner that uses a split stator capacitor, to feed open wire tuned feeders (preferably two wires held together with spreaders every couple of feet, not that solid ribbon stuff with holes punched in the dielectric).  If everything is laid out carefully and symmetrically, there will be no rf in the shack.  Plus, you have the added advantage of being able to work the entire band with top performance and a perfect match at any frequency, instead of being limited to only a portion of the band because if you QSY too far, you fear that the antenna will be "too far out of resonance" and that the SWR will be "too high".

It works much better if the feedline is a multiple of a quarter wavelength in the middle of the band, so that you may feed directly with parallel tuning (feeders attached directly to the ends of the coil, in parallel with the split capacitor), or series feed (by splitting the coil precisely at the midpoint, and feeding the transmission line directly from the gap at the split in the coil).  A simple switching arrangement can make it easy to change from series to parallel tuning, or plug-in coils may be used with the switching function automatically accomplished with the plug and jack bar assembly.

A must to avoid is any odd multiple of 1/8 wavelength, which would appear highly reactive at the feedpoint of the transmission line.  With tuned feeders, it is best to avoid any situation where the feedline has to be tapped down on the coil.  A good alternative to a homebrew tuner, if one is available, is the classic Johnson Matchbox.  Just ask Derb.

That way, one dipole can be cut for the lowest frequency band you operate, and it can be harmonically tuned to the higher frequency bands.  You have one neat, perfectly balanced dipole, not a jungle of antennas one for each band, or worse still two or three dipoles to cover from the top end to the bottom end of a single band, with all these dipoles interacting with each other and rf appearing in mysterious places.  Besides, the XYL will be less likely to bitch about the appearance of a single dipole, than about an antenna farm growing out of the roof of the house.

If more of the AM community would use this type of antenna system, there would be less whining about being forced to stay within the "Window" (the Ghetto) because it's too difficult to tune the rig to other parts of the band.

Take heed and follow the advice and wisdom of
Sensei Tom Vu K1JJ:

Coax balun....
 ;D

Dog piling is not useful. There have been numerous good answers in the thread. Give it a break.

If it were only that simple.

I love openwire and coax equally. They have their places.  I feel the advantages and disadvantages of openwire vs: coax pretty much even out. Here's why:

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.


2) When using the same openwire fed dipole for multi-bands, you lose control of your antenna pattern. Unless you are on the fundamental half-wave cut frequency, (more or less) your pattern gets sharper and sharper until it splits into a cloverleaf and then an octopus on the higher bands.  (though, multiple dipole legs would cure most of this pattern problem using openwire)

A dipole fed with coax for one band maintains the same textbook, broad, figure eight pattern.  Also, if you plan ahead and mount your dipoles properly, (computer modeling will show this) the interactions between bands are insignifcant, especially for simple dipoles.  If you want to optimize each band individually, coax is the way to go for Yagis and most other antennas. But for high impedance arrays like Sterbas, 2 half waves in phase, etc, then use open wire.  

BTW, coax can be used with multi-band antennas: Log periodics, interlaced Yagis, the new SteppIR family of antennas and trap antennas (God forbid) to mention a few.


3) Openwire is a thing of beauty for many. (I love the look) However, it is a lot of work to make properly and install. It is also a big load on the dipole (ice) and needs maintainance, depending on your climate and installation practices.

A coax feeder can be installed very quickly in comparison, is always purchased, and can even be buried. (I have 5,000' of Hardline in underground PVC pipes here)   No one even knows it's there.


4) A properly matched coax fed dipole is within a db of openwire for average feedline lengths. No one on the air could ever tell the difference, even if you could possibly do an A/B test from openwire to coax. For proof, listen to some of the BIG guns who run coax on most, if not all bands:  Gary/INR, Chuck/K1KW, Bob/KBW, Steve/QIX and many more.  


5) Coax/hardline is environmentally stable. Load it with ice, rain, acid rain, salt, etc and it has no effect. Try this with openwire and you're rowing around the band again chasing the weather.

6) A properly matched, right angle coaxial feedline -  with an unbalanced to balanced toroidal transformer to a dipole exhibits very little feedline radiation. ( a matter of degree)  When compared this way, openwire and a balanced tuner are no better at minimizing feedline radiation.


There was a time when I had FIVE JJ antenna tuners in the shack to give instant antenna switching.  (With HB openwire for each antenna)  Since then I switched to all buried hardline with instant switching on all bands. I just like the instant switching AND the ability to optimize each band/antenna to the job I wish to do.  I have five different antennas on 75M and all do a different job. Openwire would be a nightmare trying to pull that off.

I just wanted to even the debate about coax vs: openwire. They are both good and have their strong and weak points.  Ford or Chevy... :-)

Tom, K1JJ

Stevie,
 ???  Is that a coprates thing?   ;D

r.

Meanwhile Back at the Ranch.. ;D....did anybody ask this guy how much room he has...is he on a Postage stamp lot or Does he got room to Build...?

Bigger is Better... ;D

73
Jack.

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?  Would you put up two dipoles, one cut for each frequency, or would you cut one dipole for approximately 3690 and operate at whatever SWR occurred at those two spots in the band, perhaps using a "transmatch" to make the TX see a 50Ω load?

My transmitters all have multiple tuned circuits to adjust when changing frequency, so I suppose I am already used to it, and one more tuned circuit to adjust (the ATU) is no big deal.  A prepared tuning chart is a big help.

Right now my tuners are all remotely located at the base of the tower, with direct-burial RG-213 between the TX and the tuners.  Instead of  changing taps or plugging in coils, I use a separate tuner for each band, usually pre-tuned for the portions of the band I like to work, so when I change bands, I switch the entire tuner.  It is a PITA, though, to have to run down to the base of the tower to make adjustments when I QSY or change bands.  I need to get my remote control with the  reversible DC motor functioning again.  I ran over the control line with a lawn mower several years ago and have been too busy (actually, too scroteless) to fix it back.  Or else I need to run the open wire line all the way to the shack so I can locally adjust the tuners.

But one problem with a long open wire tuned line all the way to the shack is that the longer the line, the more sharply it tunes  requiring re-adjustment at ever decreasing intervals of frequency.  This shouldn't be a problem at the typical ham installation on a city lot, where the length of the feedline is likely to be a quarter wave or less on 80m and maybe even on 40.

If I decided coax was the best feedline for the job, I would either cut the dipole for the center of the band and live with the swr OR run the dipole with two legs - one cut for ~3550 and the other cut for ~3800. (3800 picked to cover the 3725 and 3885 AM areas too)  That would create quite an acceptable swr curve across the band, especially at the optimum working areas. Though, swr is not as bad as they say it is, especially on 75M... :-)  No coax transmatches, unless the solid state amplifier demanded it. 75M followed by 160 are probably the worse bands to cover the whole spectrum, percentage-wise.

Hey, that's not too bad - get this: Three of my 75M quad/Yagi directive arrays are centered on 3795. The reflectors decide how wide of a range they work. They cover about 3775 - 3820 before the swr soars. No feedline, even openwire, would solve that problem cuz not only the swr soars above 6:1, the radiation pattern reverses when way down freq..




Still it sounds like a nice system you have set up. Having to run outside to change bands is just one of the compromises of the particular configs you settled on.

Over the last 10 years, especially the last month, I've been playing with stepper motors driven by my older computer. It's for my big telescope's alt/az drive tracking and goto system. It's amazing what can be done with software these days. I can imagine what you could do with remote steppers and that tuner to automatically select various tuning configs, accurately. But the DC servos with feedback would probably be simpler.

But, yes, having the openwire in the shack with the tuner mounted on the wall is the best of all openwire whirls.

T

Put up a cage dipole or a double dipole.

--Shane

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

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

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.

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.
 

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.

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

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

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

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.

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)  ;D.

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.

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.

Then why was only ONE dog removed from the pile?

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

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

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.  ::)

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...

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

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

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 :'(

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

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.

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

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

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

Tom,
I'm looking at a 160 meter ant for the other QTH and Frank's antenna double size gives a higher input Z than a 75 meter dipole on 160. I'm torn between 2X Frank's and and a FAN dipole 130 feet long.  Hanging vertical legs off the ends will bring the ant closer to the house which has a double internal aliminum layer under the sheetrock. I would like to keep the antenna as high as possible. Also the neighbors are close.

My method for putting antennas in trees is to avoid anything like pulleys or springs.  They were always more trouble than they were worth.  I prefer to use a daisy chain of johnnyballs for end insulators, and #8  or #10 copperweld for wire.  From my experience, the tree limb will break before the antenna, and the antenna will actually immobilise the tree limbs to a certain extent.

One problem I had with a dipole was the open wire feedline.  At first I used EF Johnson ceramic spreaders spaced several feet apart.  Whipping around in the wind repeatedly and consistently caused every other spreader to break.  I finally replaced all the ceramic spreaders with home-made ones, using 1/2" plexiglass rods.  That took care of the problem until I put up the tower and replaced the natural antenna support system altogether.  Shortly afterwards, a wind storm took down the entire tree.

Since ladder lne has been re-popularized, there are numerous ways to bring it into the house and then you can avoid the lossy balun.
There are a few companies that sell a device that installs in the sash type window, enabling you to bring the ladder line into the shack.

And then you can bring it in through vinyl siding through an outside wall and hang your tuner on the wall near your shack and run coax to the tuner from the transmitter/receiver. Weaving it around the duct work and around the joists, flourescent lights, etc, in the basement can bring a lot of extra noise into your receive.
Good luck

Fred

you cant really weave it at all, or it's no longer balanced feedline.  :P :o

Interesting study, Tom.  I missed that a coupla years back.

Is this a conventional FOLDED dipole, but using a 1/4 wave flat top? Looking at Frank's  diagram I thought that the opposite point from the feedline was open like linear loading- but evidently it is closed with a jumper across the insulator? I wonder how your study would come out if the opposite end was open....   Oughta model it to see.

*** Whoops -  I see this whole subject was finally beat to death in that old thread. The opposite end is open and the specs look pretty good now.

T

Johnson spreaders work best with a center support. I have a run that has been in use since '83. I had to tighten the tie wires a couple times.

Well.......here goes...
My antenna is a 165 ft. dipole. No room for anything bigger. I feed it with home made balanced line....number 10 solid copper wire......and tune it with a home brew LINK COUPLED tuner. Works on all bands 10 thru 160.
Cant get any simpler for a compromise  antenna that has to cover all the bands. You dont have complicate a simple problem.
No stinking baluns ;)

Bill

Hi Johnathan,

My lot is just about identical to yours and I'm only about 12 miles away from you. I use a W7FG doublet at 40 feet and a Johnson kilowatt tuner.

If your interested in seeing how it's put together, stop by this weekend and have a look. Drop me an email w8bac at comcast.net. You can see more at www.w8bac.com (http://www.w8bac.com).

Mike

I had a 75m dipole fed with the brown plastic window line. It seemed to perform OK and tuned easily on all bands (except 160m) THe only problem was RFI up the wahzoo, even at low power. When the antenna fell, I put it back up and fed it with coax. I also used a coax common mode choke. The RFI problem does not exist anymore. I can use my SB-220 now and watch TV at the same time. The TV antenna is about 20ft from the dipole. Just my two cents worth.

My open wire line is just outside the livingroom about 8 feet away from the TV. Legal limit on 160 and the family doesn't know I'm on.

When I first put up my window line fed 135 ft doublet, I also had a lot of RFI.   I did some testing, I had an old voltage mode low power balun, using that the received RFI went away.   Did some measurments and found out that the so-called current balun in the commercial T-tuner was very poor on 40M and 80M, and nonexistent on 160M.  I bought a hefty balun from DX Engineering (again, no interest in the company) and it cured all the RFI problems.    The measurements also confirmed good balance.    I think that all the bad publicity here on baluns is due to the fact that most of the ferrite baluns available from most places on the internet and in tuners are mostly crap and don't work very well.    You can tell if a balun is heating up by transmitting 1KW into it for a while and seeing if the SWR changes (assuming the tuner was tuner for a match), especially on 160M with a short antenna.   Do that with a tuner with a built-in balun and you will see why baluns get a bad rep.

Hi Bob,

Yes, DX Engr uses Tom/ W8JI, to design some of their stuff. They have some really good products there. I would have confidence in their high power baluns.

I agree that ferrite baluns have gotten a bad rap cuz of the W2AU smoke-baluns and possibly from the MFJ history of blown-out baluns in some of their under-rated tuners.

In addition, most ferrite baluns are prone to EMP saturation from nearby lightning strikes too. One bad pulse and they are permanantly saturated. I suppose you could see the damage by a bad SWR if it was a true ferrite transformer. Bad beads over the coax might not show up at all.

Bottom line is, for a simple dipole, a coax balun using turns carefully wound on a PVC form is probably the most strapping way to go.

BTW, how is the DX Engr balun constructed? Does it use ferrite and is it a true transformer with wire turns or simple beads over coax sealed in a tube?

Later -

T

They explode if they take too much pulse power.

Anyone remember the air-core baluns made by B&W?  They were made as a pair of coils that looked like regular open-air Miniductor  stock, but were actually two bifillar wound, 150Ω parallel transmission lines, each wound into a solenoidal coil.  At one end, the transmission lines were wired in parallel, while at the other end they were wired in series, to give a 4:1 match.  A pair of these coils would match the 300Ω balanced transmission line feeding a folded dipole to the 75Ω unbalanced output from a pi-network or the balanced output from a low-Z link output.  A set of these  coils feeding 300-ohm TV ribbon to a folded dipole (usually also made from 300Ω TV ribbon) would be broadbanded enough to cover the entire 80/75m band and handle 150 watts or so of power.  They were designed to work 80-10m.

Don, I believe Heathkit had one like that also.     Tom, the DX Eng. baluns are heavy and large and expensive.  They are true ferrite core transfomers, they have a version made for use after tuners.    This type uses high voltage insulated wire in the windings.    My 1:4 tuner type balun is rated for 50 to 200 ohms and 5 KW continuous power.   You probably have to derate the power in actual use since it would not be anywhere near 50 to 200 ohms in actual use.  They suggest using a 1:1 for use on the output of tuners figuring you would just as likely see a lower impedance on the output, depending on your feedline length and band.   I still plan on making your version of a balanced tuner for 160M.

T Said,


This is really interesting Tom. What is permanent saturation? Please explain this if you will. Always something to learn here. Thanks

Mike

Bob, 

That sounds like a very nice toroidal transformer.  I've made  some myself that were wound on 2" toroids using Teflon wire. They were designed for 6M and worked great with little added swr.

Mike: There's not a lot on the web about lightning EMP core saturation damage. But, any ferrite core can be damaged by severe oversaturation. As far as actual effects,  I don't know if it's the heat generated that physically splits the ferrite into bits or a permanent magnetic direction sets in the atoms ... or some other type of physical damage.  But either way, the permabilty gets wasted from what it was originally.

I'm sure someone here will know the inner scientific details... :-)

T

Thanks Tom

My first (only) guess was magnetism. That is an interesting subject. Maybe Stu will chime in.

Mike