Balun help

[Detroit47]

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

[K1JJ]

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

[Steve - WB3HUZ]

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.

[W2PFY]

What is a Balum?

She's the Governor of Alaska

 

[WB3JOK]

What is a Balum?

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

[Detroit47]

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

[k4kyv]

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

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

[WU2D]

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

[W3SLK]

Jonathan said:

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.

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!

[K4TAX]

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

[K1JJ]

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

[Steve - WB3HUZ]

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.

[W3RSW]

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.

[K1JJ]

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

[w1vtp]

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

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

[KD6VXI]

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

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

[K3ZS]

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.

[k4kyv]

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.

[Jim KF2SY]

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

Coax balun....
 

[Steve - WB3HUZ]

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

[K1JJ]

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.  

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

[W3RSW]

Stevie,

Dog piling is not useful.

   Is that a coprates thing?   

r.

[ka3zlr]

Meanwhile Back at the Ranch.. ....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...

73
Jack.

[k4kyv]

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?  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.

[K1JJ]

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?

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..

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.

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