Copyright © 2002-2019 by Harold Melton, KV5R. All Rights Reserved. Rev. 02/19/19

### Spacing and Impedance

Don’t worry about it. A non-resonant antenna will present a feed point impedance of perhaps 35-5000ω, at various frequencies, so who cares about the exact feed line impedance? Matching the antenna to the feed line simply has nothing to do with efficiency (unless you’re using coax).

Anything from 1 to 6 inches is acceptable spacing. 1-inch #14 line is 370 ohms. 1-inch #18 line is 450. 6-inch #12 is about 600. It just isn’t at all critical - and don’t let any geezer or guru tell you different! The spacing should not be over 1 percent of the highest-frequency wavelength, and that’s the only real consideration with ladder-line spacing. On the other hand, it needs to stand-off from metal at least 2-3 times the line's width, so wider lines need longer stand-offs. I think 4-inch open line, with 12-inch stand-offs, is a good place to start.

### Length

As mentioned above, parallel feeders can pick up RF from the antenna and transport it into the shack as common-mode current (this means the two wires acting as one, in-phase). The way to avoid this is to avoid resonant lengths of ladder-line, and, if possible, bring the line away from the feedpoint perpendicular to the antenna (90°) for a far as possible before turning parallel to one side of the dipole. Setting your bend-point will also help you take up slack when using a non-resonant length, without having to cut off the excess.

In other words, measure your total run, then increase that to the next available “good” number, then route the line to take up the slack. A 300-foot (or 100 meter) open-reel tape measure is handy, and Harbor Freight has them for about $20.

Lengths to avoid (in feet): 32, 65, 96, 130, and 260 - and multiples of any of those. Don’t let them make you buy 100 feet when you know that’ll be too close to 96! Make them sell you 110 feet, for example.

Good lengths: Somewhere around 40, 80, 110, etc. This is from the ARRL Antenna Book.

### Ladder-Line Length, Update 2019

Since writing this article in 2002, I’ve discovered there are several theories about calculating ladder-line length. It turns out that the ARRL Antenna Book is right about using non-resonsnt lengths, but that doesn’t present the whole picture. Common-mode currents may be effectively blocked with a good 1:1 current choke/balun.

However, there’s an even better reason to select non-resonant feed-line lengths, and that is: To avoid impedance extremes, and present an easy match to the tuner.

#### The Odd-Eighth-Wave Method

Various experts are now recommending that such systems should use **odd-eighth-wave multiples** of the antenna’s fundamental frequency. The easy formula is:

LL(feet) = 123 ÷ MHz × VF, x1, x3, x5, x7, etc. Since full-wave (feet) = 984 ÷ MHz, eighth-wave = 123. If you want to get it really close, multiply that by the Velocity Factor, which is about .91-.92 for window-line, and about .95 for insulated open-line.

Example: Dipole resonant at 3.75: (123 ÷ 3.75) × .91 = 29.848 feet; x3 = 89.5; x5 = 149.24; x7 = 208.9; etc. Not to imply it’s that critical — we just need to ensure that no current or voltage anti-node falls within any amateur band, to the greatest possible extent.

The reasoning is that such lengths will place impedance extremes *between* bands, and more moderate impedances *within* bands to make it easier on balun and tuner components. Or, put another way, keep the voltage and current anti-nodes out of the ham bands, and therefore, away from the tuner. For example, a certain length of line that is odd-eighth-waves of the fundamental will transform the low impedance of a current anti-node *up* to perhaps 500, and at double that frequency, transform the very high impedance of a voltage anti-node (like running an 80-meter dipole on 40 meters) *down* to around 500. So the tuner never sees an extreme mismatch, and we avoid both overheating things with high current, and arcing things with high voltage.

NOTE that I did NOT say using an odd-eighth-wave WILL give you 500 ohms on all the ham bands. I just picked 500 because it’s the approximate geometric mean of antenna impedance extremes, to use examples to explain the concept. If you have a VNA, feel free to do some experiments and let me know what you found.

Transforming both low and high impedances to *medium* impedances is also desirable because antenna tuners are less efficient with low antenna-side impedances, and are the most efficient when the antenna side sees impedances around 500Ω. See also, charts in G3TXQ’s Tuner Balun article.

For example, if our long and low dipole has a feedpoint impedance of around 25 ohms (a typical case for 75-meter dipoles well under 1/2-wave high) at resonance, and we duplicate that at the tuner end by using a half-wave of feed line, the tuner sees 25 ohms and its efficiency is a poor 60-70%. And if we use an odd-quarter, we invert the low impedance to extremely high, and things start arcing. But if we use an odd-eighth feed line, the tuner will see several hundred ohms, and its efficiency soars to around 95%! The extremes are still there, but they are an eighth-wave up the line, not at the tuner’s terminals.

Now when we double the frequency (160 to 80, or 80 to 40), suddenly we are running a full-wave dipole, and feeding a voltage anti-node, with a very high impedance. If we duplicate that at the tuner (with a half-wave of line), we arc the capacitor plates with high voltage, causing tuner damage (and maybe amplifier as well). Not good! Odd-eighth-wave to the rescue—it will transform both low and high impedance to medium, right where the tuner is both safe and efficient! Nifty.

I used 5/8ths-wave with my 80-meter (130') doublet, and found that it tuned well on all but 10-meters, so I had to trim the line a little. There is no magic number or formula for ladder-line length, because every antenna is different. But the odd-eighth-multiple is a good place to start.

#### Tuner Manuals

From the MFJ-976 Balanced Line Tuner Manual:

“The following suggestions will reduce the difficulty in matching an antenna with a tuner:

- Never center feed a half-wave multi-band antenna with a high impedance feed line that is close to an odd multiple of a quarter-wave long.
- Never center feed a full-wave antenna with any feed line close to a multiple of a half-wave long.
- If this tuner will not “tune” a multi-band antenna, add or subtract 1/8 wave of feed line (for the band that won’t tune) and try again.
- Never try to load a G5RV or center fed dipole on a band below the half-wave design frequency. If you want to operate an 80-meter antenna on 160 meters, feed either or both conductors as a long-wire against the station ground.
- To avoid problems matching or feeding any dipole antenna with high impedance open wire lines,
keep the lines around these lengths. [The worst possible line lengths are shown in brackets]:

160 meter dipole: 35-60, 170-195 or 210-235 feet [Avoid 130, 260 ft]

80 meter dipole: 34-40, 90-102 or 160-172 feet [Avoid 66, 135, 190 ft]

40 meter dipole: 42-52, 73-83, 112-123 or 145-155 feet [Avoid 32, 64, 96, 128 ft]

Some slight trimming or adding of feed line may be necessary to accommodate the higher bands.”

Several other balun and balanced-line tuner manufacturers offer similar numbers. Good advice from them, but to me it’s just simpler to calculate an odd-eighth-wave multiple and put those impedance extremes between bands. What about 60 and the WARC bands? Well, you might not avoid an impedance extreme in *all* of them, but if you have trouble tuning a band, trim a little feed line and move the impedance extremes a bit. How much to add or subtract? An eighth-wave on the band that will not tune. Makes sense, eh?

#### What About “Skywire” Loops?

Myth (heard nightly): **“Horizontal loops only radiate straight up!”** Really? How is it then that many hams use them with great success, both regionally and, on the higher bands, for DX? The elevation pattern for a full-wave horizontal loop is almost identical to a dipole at the same wavelength high. High-angle NVIS on 160, 80, and 40; and lower angles on 20 and above. The loop also suffers in the azimuth plane from multiple nulls and lobes on the higher bands.

Keep in mind that a full-wave loop is resonant (~100*j*0 free-space, lower near earth) on **every** multiple, not just odd multiples like a half-wave dipole. That means that a 160 meter loop cut for ~1.78 MHz (1005 ÷ 1.78 = 564 feet) will be current-fed also on 80, 40, 20, and 10.

Like the big multi-band dipole, the big multi-band loop works best at about 68 feet high, where it’s a half-wave high on 40 meters (but it’s still okay at 30-45 feet), and ladder line feed. Please see NVIS Page 3 and the elevation angle plots therein.

Articles still abound, from the original *Loop Skywire* article decades ago, to the present, showing the “Skywire” fed with coax. And everyone I’ve ever known, or heard of, who did so was disappointed. But those that feed big loops with ladder line say they will never go back to dipoles, or coax.

Continued…

Hi,

Very informative site and Q/As! I have a doublet that is 160′ long that is resonant at 3.5 MHz with 90′ of window line. I can easily tune down to less than 1.2:1 on 160-6 Meters with the Elecraft KAT500 tuner.

I have modeled this antenna in EZNEC with decent results and am wondering if ‘more’ length on the elements with appropriate trimming of the ladder line would improve the efficiency on 160 and 80, where I operate the most. I was thinking of making it resonant close to the center of the 160m band and then using approx 1/8 or 3/8 WL for the feedline. In your opinion, would the effort to increase the capture area of the antenna by 80 ft or so (some of which may be dangling vertially down over tree branches) result in any improved signal strength?

Of course the other concern in doing this, is it currently tunes fine on all bands and gets me good reports. The extra length may cause problems on the higher band. Maybe I’m trying fix what ‘ain’t broke’.

Your thoughts?

Rick kc2fd

Howdy Rick,

The antenna would have a little better efficiency on 160 if a half-wave long, but then on 80 it would be 4-lobed, and more lobes on higher bands. If it’s working for you, I’d just stick with it as-is.

73, –kv5r

Sept 17, 2020

Greetings Harold,

I am in the process of building an Open Ladderline fed 1.8Mc Dipole antenna using information on your website. My questions center on paged three (3) of the Ladderline article.

In building this antenna, I have two formulas for determining length of the dipole portion of the system.

468 divided by frequency in Mc times 2 for total length in feet.

Example: 468/1.800 times 2= 520 feet. 520 divided by 8=65 feet, x3=195 ft, x5=325 feet etc.

300 divided FMc times 39.37 divided by 12 = total feet in length.

Example: 300 divided by 1.800 times 39.37 divided by 12 =546.8 feet divided by 8=68.35, x3=205, x5=341.75 etc.

My question is which one should I use. There is quite a large difference in base lengths to consider when using the 1/8th formula.

When I studied page 3, I just could not understand where the 984 came from. I used the above formulas and got close to the idea except which formula to use. I have answers for either formula. Later down the page there is a list of recommended lengths to use. None of my answers could meet those numbers.

My antenna location is about 400 feet +/- from the radio shack. We have small farm, of 18 acres, mostly hay fields with a few trees (towers) The feed point will be approximately 40 to 50 feet after the sag above the ground. The recommended chart does not cover feed line lengths above 250 feet or so, which has me wondering in building and using the 1/8th formula, what would be a good length to use.

When you have a few moments, I would appreciate your help to get me on track. Feel free to call. Text me your calling number or email it so I will answer it when you call. We do not answer unknown numbers.

Thank you and Blessings,

Paul L. Eakin, KJ4G Good on QRZ

1063 Glenlock Road

Sweetwater, TN 37874

850-591-0442 Voice and text, Hours 09:00 to 21:00 EST

Howdy Paul,

I don’t know where you got either of those calculations. There is no “times 2” in a dipole calc; total length in feet ~= 468/f(MHz), a 160 meter dipole is always about 250-260 feet long.

There is no “300” constant related to feet; 300/f(MHz) = free-space wavelength in

meters, because light speed is ~300 million meters per second.984/f(MHz) = free-space wavelength in feet, because light speed is ~984 million feet per second.

Half of that, 492, is a half-wave in free space. In wire, due to velocity factor and length:diameter ratio, that 492 is reduced to about 468.

984/8 = 123/f(MHz) = an eighth-wave free-space, in feet. Multiplying that by the velocity factor of open-wire ladder line, about .94, gives about 116/f = eighth-wave in ladder line feet. Multiplying that by odd numbers should give acceptable lengths of ladder line, (i.e., avoiding the impedance extremes at odd-quarters).

But that’s not the end of the story, because what’s acceptable at 1.8 MHz may present problems on the higher bands. So the end of the story always becomes trial and error. Or, as one of the antenna tuner manuals says, if one band won’t tune, remove an eighth-wave of line

for the band that won’t tune.For example, a typical problem is on 10 meters, and removing (or adding) 3-4 feet will fix it (think about it: on 10 meters there a “bad” spot every 8 feet!).Make your dipole 260 feet, and run your ladder line to your house, with an extra 8 feet or so in a U-shape for trimming if needed. Use a 1:1 current balun/choke and a big-ol’ manual tuner.

That’ll work just fine!

73, –kv5r

Hello Harold,

Does the Odd-Eighth-Wave Method for LL length hold for very long non-resonant antennas also? All your examples are for dipoles cut for specific ham bands. How would you calculate LL length fo a “V-Beam” antenna 390 ft. each leg about 60 degrees apart?

Howdy Mark,

The idea of the odd-eighth applies to situations where the feed-point impedance of an antenna is low on one band and very high on the next (harmonic) band, and you want to avoid these extremes at the tuner.

With an antenna that’s non-resonant on any band, LL length is just trial & error — add or remove an 8th-wave at the frequency where the tuner won’t tune it (if any).

73, –kv5r

Harold,

Well, trial and error cutting of the 4″ #14 wire homebrew LL only got me 10, 15 and kinda 20 meter operation on the 390 foot V-Beam\doublet. But when I bypassed the 1171 Balun and went straight into the Johnson Kilowatt tuner I was able to load up on 80 through 10 with no problem. Should I be looking at a 4:1 or 6:1 balun for my setup?

Mark – WA2FXM

I would say no. The Johnson Kilowatt Matchbox is a balanced tuner, so you don’t need any balun. And if it’s tuning 80-10 you don’t need any extra transformation ratio. The tuner itself is a balun and a variable-ratio transformer.

73, –kv5r

Hmmm, I’ve still got a lot to learn here. So the 1171 works for you because your 989D tuner is unbalanced?

No, but I don’t know why the 1171 didn’t work in your system. It’s just a common-mode choke, two parallel wires on a core. Maybe because it add several feet, maybe it has a bad connection inside.

A current balun is 2 or 3 things: a balun, a choke, and optionally, an impedance transformer. Various designs accomplish these tasks to varying degrees of success. And the degree of success of each task also depends on core material, frequency, and impedance of the line at that point. So for example, a 2-core 4:1 balun may lose most of its choking ability (and it does) when it’s design impedances are 50:200 but you have like 20 or 2000 ohm load on it. Or may fail to perform as expected “here” in the line, but cut a few feet off and it works great.

A line with standing waves acts as an impedance transformer, so you can call it a “450-ohm” line all you want, but it just isn’t, unless you have a 450 load on it (flat SWR at 450). But when mismatched (high SWR) the 450 (or 300 or 75 or 50, whatever), actually has a

variableimpedance along its length, so then its “characteristic” impedance is rather meaningless. The rate of variation depends on the frequency, and the amount of variation depends on the SWR.So here you have your typical ham, presented with a nonresonant doublet, some 450 ohm line, a tuner, and a transceiver, who assumes that a transformer balun is needed to get the impedance of the line (450) somewhat closer to the 50, so the tuner sees an easier match — but it just doesn’t work that way at all! The ladder line is always mismatched at the antenna, so always has standing waves (impedance variations) along its length, and the impedance the balun and tuner sees might be 20 ohms or 3500 ohms or anything between, and it changes with frequency and line length. So we now see that putting in some ratio of transformation is pointless, on a multi-band doublet.

Similarly, not understanding “balanced” and “unbalanced” causes much confusion and consternation. A parallel line may easily be unbalanced (like put an OCF dipole on it), and a coax may be balanced (like if the shield to RF ground path is interrupted by a choke). It is by no means accurate to say that “unbalanced” is an inherent characteristic of coax, or that “balanced” is an inherent characteristic of ladder line. Rather, it’s more accurate to say they are conditions under which the lines are operated, e.g., the whole system’s environment; like, balance at the feed-point, is one leg RF grounded (thus, longer), and is there common-mode current induced by the antenna onto the shield of coax, or both conductors of a parallel feeder.

Well, that’s all nice and confusing! We have all these variables, some known, some assumed, and some unknown, and it’s like herding cats! There are no standard recipes that’ll work in every case, so the easiest path is to put up a half-wave dipole, feed with ladder line, then play around at the shack end until it just works. If you want to make predictions, you model the antenna in EasyNec or 4nec2, export a sweep to an s1p file, use that file as a load in SimSmith, define your transmission line and tuner, then sweep the whole thing and make pretty graphs. But OOPS! After all that work, you still end up putting an antenna up and just fiddling with it until it just works, and all the recipes and theories and modelling are an interesting learning experience but in the end must yield to the empirical realities of the system in its environment.

In your case, you have a LOT of wire in close proximity to lossy earth, and likely have a very low radiation resistance (a few ohms) at the feed-point. It might benefit from putting like a 12:1 transformer at the feed-point, with the low side to the antenna and the high side to the ladder line — but wait! — depending on the length of the ladder line, the other end might be extremely high impedance! Or it might be great on 80, but you go to 40 and it’s extreme. And harmonics don’t fall where expected, because earth loss pulls it out of kilter, the antenna being different wavelengths high on different bands.

Anyway, too much rambling on!

TL;DR – The best way to get your mind around baluns is G3TXQ’s site, http://karinya.net/g3txq/ — in the index see What Tuners Do, Tuner Balun Ratios, RF Chokes, Baluns, Transmission Lines. And save the excellent PDF http://karinya.net/g3txq/baluns/baluns.pdf . I just blather in generalities, but he knows what he talking about! 🙂

73, –kv5r

This a copy of an email sent to ****@kv5r.com

I got a permanent out of service.

Good morning Harold,

Thank you for your website. I am learning a lot of good info.

On page 3 of ladder lines I am confused about widths and impedances.

It is stated that different gauge of wire, different distances will have corresponding impedance values.

Where I am confused has to do with an advertisement by “trueladderline” which is advertised as 600 ohm lined and the gauge of wire is 16 and the distance is 3 1/2 inches wide.

If I were to build my own ladderline, which formula should I use to have a working feed line?

I was understanding for 600 ohm line the distance would be approximately 6 inches.

600 ./. 50=12 for a ratio.

My question is which balanced balun should I use for either the “trueladderline” antenna or if I build an antenna, what size ladderline would be best to make?

Another question concerns the balun at the xmitter site. I believe both you and DXE have stated that a 1:1 current balun would be the better choice.

The antenna(s) we are planning to build; first to get on the air is a ladderline fed 80M dipole. It will require approximately 550 feet of feed line. We are farmers and have very few trees close to the homestead.

Second, we are planning on building a horizontal loop tuned to .900 Kc (middle of broadcast band) at 40+ feet. the loop would be pentagon shaped (5 sided and closer to a circle shape) and its feed line would be approximately 300 feet. All LL’s would be measured using the 1/8 rule to the next level.

Any assistance would be greatly appreciated. Also any antenna comments would be appreciated.

You are welcome to call.

Hours are 08:00 EST to 21:00 EST Daily; Sunday 14:00 EST to 21:00.

Blessings,

Paul, KJ4G

Check QRZ page for more info.

Howdy Paul,

Must’ve been a glitch; my email is good.

There’s a formula in the ARRL Antenna book (as well as on-line calculators) for parallel transmission line impedance, given wire size and spacing. I just checked one; for #16 wire, 600 ohms is at 3.7 inches. The old “rule” about 6″ = 600 ohms is for #12 wire. 4″ with #12 is still 550 ohms.

But it really doesn’t matter, because unless the line is terminated into its characteristic impedance (which it never is with such antennas), you have standing waves on the line — the impedance varies widely along the line, and anything from 300-600 will work. For such a long line (550′) I think 3½-4 inch line should do fine. I run 150′ of #10 4″ line here. For your long runs, I’d not use #16; 12 or 10 would be better.

Yes, a good 1:1 current balun/choke is recommended. I use the Balun Designs 1171. It’s just excellent, and under $100.

I think your 900kc loop will do better all around than the 80 meter doublet, and 300′ of feed is better than 550. Since loops are resonant on every harmonic, you’ll have a dip about every 900kc up the band, but don’t expect them to fall in every ham band, because proximity to earth “pulls” the resonances off of their expected harmonic points. Just adjust the ladder line length if needed to get the tuner end in range of the tuner.

Here’s my doublet; might give you some ideas – https://kv5r.com/ham-radio/2018-projects/80-meter-doublet/

73, –kv5r

Hi Harold,

Great information to help me with my first Doublet install. I used to use fan dipoles but too many wires in a windy location and difficult to tune with the interactions of the wires on each other.

I hope I can explain my question clearly enough. I am installing an 80M doublet (although I will only be using it on 40 and higher for now). I have adjusted the radiator length to be resonant on 3.37 MHz so I can get a boost on 30M on the 3rd harmonic. My question on window line length is which freq do I put into the formula for odd 8th-wave? The frequency the antenna is cut for?

Many thanks,

Scott ve3vvf

I’d start with the frequency it’s cut for, but you’ll just have to try it and see. The usual trick applies here: cut or add 1/8th wave at the band the tuner won’t tune.

73, –kv5r

That’s great, thanks so much!

I have enjoyed following this web site for some time now.

Here is what my antenna setup is.

242′ of 14 gauge wire then 57′ of 600 ohm ladder line going down to a 4;1 Balun designs balun. Then 75′ of LMR 400 coming into the shack to my Palstar AT2KD tuner. I can tune 160, 75, 80, 40, 20, 17, 15, 12, 10.

Direct 160 is around 5:1 swr. 80 is 3:1 swr 40 is 40 is 5:1 swr 20 is 2:1 swr 17 is 5:1 swr 15 is 5:1 swr 12 is 3:1 swr 10 is 2:1 swr.

When I use the tuner I can tune flat completely except for 160 the best is 1.2 :1 swr.

The antenna is up around 63′ apex and 60″ east end and around 30′ west end.

All in all I am very pleased with the setup and it was all because of reading this web site and going to the trouble of making it work.

Thanks for the site.

73, DJ

VA3KBC Check out the pictures on my QRZ site lots to see.

https://www.qrz.com/db/VA3KBC

Howdy Don,

Glad you found my articles useful! Looked at your lovely home site & stuff on QRZ – if I had a place like that I’d be in heaven! And you’ve done such a nice job on the antenna installations!

As you can see, I’m a big fan of big doublets & ladder line, because they are simple, cheap, and work better than most people expect, without any “magic antenna” nonsense.

My problem here is just way too many trees; I can’t put up the antenna I’d really like, which would be a 160 meter loop over my wet meadow area. But the 80 meter doublet I did manage to get up in is doing fine.

Thanks & 73,

–KV5R

Some day I would like to put up a full length 160 meter loop. I just need 2 more 60′ Self support towers. I had a chance to get one and was going to put up a Delta loop. But it didn’t happen yet. If I can get one I would like to try a delta or should I wait till I get 2 more towers and do a 4 corner style loop?

I do get great signal reports and really enjoy 40 meters on those cold winter afternoons.

160 at night is great as well.

I was wondering if it would be worth while to lengthen the wire from 242′ to 250′ ?

I don’t think the difference between a dipole and a loop would justify 2 additional towers. The loop will have a

veryslightly lower elevation angle on the low bands, and a different azimuth pattern on the higher bands. You’d need to model them in MMAna-Gal or EZNEC to see.Lengthening your 160 meter a few feet will move the low impedance points around and change tuner settings, while not improving performance by any noticeable amount.

Probably your most direct route to significantly better performance on 160 would be a quarter-wave vertical, e.g., a 130′ shunt-fed tower over a giant field of radials.

Take a look at W8JI web site, he has an impressive antenna farm (including a 160m 4-square array) and knows how to model & engineer all that stuff.

-73, –KV5R

Well that is good to know. It will save me time, money ans effort.

What I really need to do is get the west end up higher and off the tree. I might get a 4×4 or 6×6 post in the ground before the tree and tie the end of the antenna onto it.

I was also looking at your site and holy smokes you have LOTS of trees to contend with.

I would think you could possibly take down a few so you had a path for a 160 antenna. I love 160 in the winter!!

Thanks again for the advice and this great web site.

73, DJ

VA3KBC

Good morning, just read your article on ladder line feeds. I have a Vee apex’d at about 85 feet on the tower, cut for 3.500 and fed with 170 feet of 450 ohm ladder (1″ wide, 1″x1″ windows) line. Tower is 80 feet from the shack. Using a Johnson KW Matchbox to do the tuning/matching

From what I understand from your article and the formulas, that ladder line needs to be either 175.714285714 feet (123÷3.50×5) or 246.000000001 (123÷3.50×7). Did I get it right? Are these good lengths to support using the Vee as a multi-band antenna? Do I need to add about 5-foot on the existing ladder?

No, it isn’t that critical. As long as the tuner will handle it, you’re fine. If you have a band that won’t tune, change the line length by 1/8th-wave of that band.

So i am making one of these long loop antennas. i can fit 537′ of wire where it is going. i am building the true open ladderline and i bought a 2:1 balun, from there about 6ft of coax to the amp. Will the 2:1 balun work? it said “loop antenna matcher” on the description.

A full-wave loop has a free-space feed-point impedance of about 100 Ohms (but much lower when only a fraction of a wavelength above ground), and a 2:1 would make even lower. I would suspect that a 2:1 balun marketed as a “loop antenna matcher” would be for a relatively small and high loop (like the driven element of a quad array), where the feed-point would actually be close to 100 Ohms, and the feed-line is 50-Ohm coax.

Feeding a big full-wave horizontal loop with ladder-line is the best way, but you need determine what you’ll actually need to tune it, assuming you’ll be operating it on several bands.

I recommend that you contact Balun Designs’ owner and ask him. He’s probably gonna say get the 1171 and a big ol’ antenna tuner. I just installed an 1171 for my open-wire-fed 80 meter doublet (used as a non-resonant multi-band with a tuner) and very happy with it. See: http://www.balundesigns.com/baluns-for-loops/ .

73, kv5r

I think your right a 1:1 common mode choke but I may also need a transformer. If I just have the 1:1 balun or current choke I will have 50 ohms impedence(coax) going to that window line that is about 600 ohms.That may over heat that 1:1 balun. Going to coax I think the match may need to be closer. If I added a 12:1 transformer it would be 600 ohms to 50 ohms correct? The 1:1 to take care of any common mode current, and the transformer to go from the coax to 600ohm window line?

No, you don’t need a transformer. All you need is the 1:1 choke balun.

It’s a common misconception. The

characteristicimpedance of a feed-line is only meaningful when the line is terminated in a non-reactive (resonant) load with a feed-point impedance the same as the line, i.e., no standing waves. For example, a resonant folded dipole (300 ohm feed-point), fed with 300-ohm LL, and a 6:1 balun at the radio, would be a proper use of a transformer balun. But that’s not frequency agile.The impedance you’ll have at the LL to coax transition will vary widely (~25-4500 ohms) depending on the length and height of the antenna, the length of the feed-line, and the operating frequency. It’ll zoom up and down as you spin the dial.

In any feed-line with standing waves, the impedance varies from low to high every quarter-wave along the feed-line. That’s what standing waves

are— impedance variations along the feed-line.73, –kv5r

Hi there – this is a great resource. Thank you. I have a quick question. I currently have a 44 foot doublet fed with 51 feet of 300 ohm slotted twinlead – via a 1:1 current balun with a short 1 foot jumper into an LDG Auto Tuner. It tunes 80(!) to 12 down to 1:1 swr, but NOT 10m (can’t find a match on 10m better then 3:1 – ironically tunes fine on 27mhz). Can you suggest an alternative ladderline length to incorporate 10m, bearing in mind my 44 foot doublet length? Thank you – I truly believe doublets fed with ladderline are the way forward. 73

Hey Tim!

Yeah I have that problem with mine, too. Hard to tune on 10M. A don’t know how to calc your antenna, but a + or – 8 feet or so will rotate your impedance about 90 degrees on 10 and may put it within range of your tuner.

I need to do the same with mine! Drag out the dang ol ladder, soldering gun, tape; yeah, maybe I’ll do that, next week! 😉

If you do find a good number please report it back here for all to benefit.

I’m working on a new page about ladder line length but my own system is giving me fits so it’ll be a while. Good ol’ experimentation!

73, –kv5r

Thank you for providing so much valuable information on your site. I shared your NVIS article with several hams. I think it’s one of the best, if not the best I found online regarding NVIS.

As far as this topic, I would appreciate it if you could confirm what I think happens in my case. I have an OCFD that I feed into a 6:1 impedance transformer. The SWR right under the balun is about 6:1. My coax is about 15 ft long. Based on your calculator, that’s a roughly 10% power loss. If I lengthen the coax, the power loss increases (rather rapidly). So far, so good.

My question is this: does the impedance transformer play any role in power loss? My guess is that any power loss would be pretty small, depending on how well the balun was built. Am I correct in assuming this? Thanks.

Yes, all baluns have some loss. It could range from negligible to terrible, depending on the balun design, mis-match on the load side, frequency, etc. You shouldn’t have a 6:1 SWR on the coax side, that would seem to indicate you’re using the wrong ratio balun or need to move your OFC feedpoint.

But I’m no balun expert! It’d be better to ask someone at DX Engineering or Balun Designs.

Thank you for the reply. Yes, I must have the wrong ratio balun. Unfortunately I can’t move the feedpoint (HOA limitations). My options are to use a tuner to take care of the SWR (my current setup), or experiment with rolling my own balun and see if I can bring down the SWR.

Thanks for sharing all your expertise and experiences.

I am a new General Class ham w/o an Elmer to guide me so I try to research all that I can on the Internet.

Perhaps you could comment on my situation using window feed line. I am using a W5GI “mystery” antenna on which the maker has installed a window ladder line with some sort of a connector to convert the ladder line to coax. I have used this antenna with success by connecting the coax connector on the feedline directly to my MFJ939 auto tuner. The feedline comes through a double hung window and is only inside the shack for about 2 feet. There have been no apparent problems with the antenna tuner or any equipment.

I recently bought a “my panadapter” so now I am running my laptop computer alongside my transceiver. I am now finding that on the 20m band, and higher frequencies, that the computer is affected by my transmissions. I assume that it is RFI. I am not sure how to find out just what it happening and then how to mitigate the problem.

Any words of practical wisdom you can offer will certainly be appreciated.

I also note that you are in favor of a voltage balance at the output of the tuner, but I am not sure to exactly to tell if my tuner has one.

Thanks,

Bill

KD8WMJ

Your 939 doesn’t have an internal balun. Get a good dual-core current balun, outdoor type, run a short coax to it outside. That’ll reduce your RFI. If still getting RFI, get some snap-on chokes and put them on your computer’s cables. Also make sure your radio & tuner are well grounded.

73, –kv5r

Hi,

Thanks. Just one last point about the dual core current balun. Should it be 1:1 or 4:1 or other? I assume it should be 1:1 as the antenna builder should have taken care of impedance marching in the included ladder line to coax connector.

Bill

KD8WMJ

I don’t know anything about the W5GI mystery antenna. Probably should ask the people that sell it.

Sir, superb feedline write-ups. Like you, I’m astonished at ik1mnj’s use of LL. What a guy!

Question: I will be feeding a U (or C?) shaped doublet with ladder line soon. Unfortunately, there is no other way of achieving the feedline path other than to creep along the ground, a few inches off the deck, almost underneath the antenna will be around 25 and 30 feet high. Primary bands for this doublet will be 160m and 80m.

I’d love to go perpendicular, but parallel is the only way. Am I in for serious trouble?

Regards, Callum.

NAAAA! It’ll probably be okay.

I ran a 160M dipole with ≈75′ of ladder line parallel and 20′ under a leg and it was okay, at least on 100W.

33-1/3,

—kv5r

Thanks fella. I’m going to be up around 500 watts RTTY, but I’ll give it a go anyway!

Finally Harold, I think you might know the answer to this one. I want to run another LL feedline to the attic. It’s a complex route and I already have 6 x coax lines in a bundle I installed years ago, mostly unused. I’d like to use 2 of these feeders in parallel for about 10 feet (which is part of the bundle), just where the complex route starts and ends up through some roof tiles etc. I can either extend this pair of coaxes to the tuner and ground the braid to the back of the AT4K (big fat tuner) and then when I get to the attic, split it back to LL, or I have the option of starting with LL, going to parallel coax for the difficult route and then back to LL again. Of interest, I could ground the braid to a redundant earthing system I have that nothing else is connected to to get rid of any electrostatic build up? Many conflicting reports here across the internet. I’m starting to consider just building a new route just for the attic project..!

Cheers, Callum (Birmingham, England)

Hi Callum,

I think you could extend 2 coaxes to the tuner and ground the shields there, with no problems.

At the other end, where you connect the LL, tie the shields together but do not ground them.

That’s the usual way STP cable works, you have 2 parallel conductors, with shield(s) grounded at 1 end.

If you run LL from your coaxes to the tuner you’re just asking for more RF in the shack.

73,

–kv5r

Harold hi, i’m ik1mnj Henry, I read your interesting articles on the open wire line, I fell in love with this type of power antennas to the point that I removed all coaxial cables that fed all my antennas 6 m. to 40 m. and I fed my antennas with 450 homs windowed open wire line, duly kept away from the boom of about 10 cm, with different brackets of insulating material, all power supplies from their radiators, go to an intermediate point on the boom where I put a switch 10 positions made with 16 amp plug relay, from this point (length equal for all bands) descends into the station outside the wall where I put a 4: 1 balun, and go into the station with a few meters of coax RG213, just a hard job !! see my web site, the whole system works very well but I have met some problems still not completely solved, these are my questions: 1 ° when calculating the non-resonant length for the various bands I have to take into account the velocity factor of the line, that in the case of 450 homs should be 0.90, 2nd in my case because I have different lengths from the respective feed points to the switch, it becomes difficult to obtain a non-resonant length that works for all bands, of course, I wrote down the lengths added together for each band, from the feed point of each band up to the balun, what could I do? use different lengths of RG213 cable from the balun on the radio station? (in this regard I would like to have your opinion on my work, thanks in advance) thanks for your interest in Harold, 73′

Hi Enrico,

I located your nice web site and your ladder-line page with all the photos. That’s one impressive antenna system! And probably the most complex use of LL in the world. I would not have thought it possible to feed so many directional antennas on one boom with LL. Your experience is far beyond mine — I have only fed single and crossed dipoles, and a 2-meter yagi, with LL.

1. On velocity factor: I think that VF is not considered when determining non-resonant lengths of LL in common-mode (in-phase, acting as a single wire). VF is only considered in differential mode. In common-mode there’s almost no dielectric interference, well, it’s like a single insulated wire, so about .98-.99.

I think in your case getting all those lengths to be non-resonant in common-mode will be impossible (many bands and many more harmonics). If your problem is RF in the shack, try a choke on the RG-213 (~10 close-fitting ferrite toroids stacked), near the balun. That should remove RF from the outside of the shield.

You should also choke your relay and rotator cables; everything that comes from tower to shack can act in common-mode to bring RF indoors.

If that isn’t enough you might also need to use snap-on chokes on various cables in the shack that connect to the affected equipment. There is also the whole topic of eliminating ground loops.

2. LL crossing rotation point: Just make a larger C-shape of LL. If the C-loop is large enough it won’t touch the mast when turned, it will half-spiral around the mast when turned 180° from center.

Please let us know how it all works out!

73, –kv5r

What can be done wit excess length if the natural length to the back of the tuner happens to be 65 feet? Can the extra 15 feet of ladder line needed to get to 80-foot total length be looped or coiled some way without detrimental effect?

Yes, the slack can be hung in a large, wide loop, but no don’t ever coil it.

You might put a couple eye-hooks several feet apart under an eve, or tie some nylon string through window line in a horizontal run and tension it, either way, turning the slack into a big U-shape, or even several U’s, as needed. Just don’t coil or roll it up, you don’t want it touching (or near) itself to where the magnetic fields would interfere with each other.

73,

–kv5r

Does the good length and bad length the same for 450 ohm ladder line? Or is there a formula to use to calculate the appropriate length.

Yes, the lengths given should be OK for any kind of parallel-wire feedline. The formula would be 492/f=feet, where is f is frequency in megahertz, and you pick a frequency that is right

betweenham bands, to get a non-resonant feedline length. Then you also check the odd harmonics (f times 3, 5, 7) to make sure they are also between bands.