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600 Ohm Ladder Line vs Coax

Discussion in 'Amateur Radio Antennas' started by Robb, Jul 18, 2010.

  1. Robb

    Robb Yup

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    Since I'm about to put up a dipole; should I use 600 ohm ladder line? Many Hams consider the 600 ohm line better than the 450 and 300 ohm stuff. Why is that so?



    Why is it preferable to coax? What are the advantages? What are the disadvantages? Should I use a specific length for a given band of antenna - say a 10-80m fan dipole?

    I believe a Balun would be needed. Because it is a 600 ohm feed; what balun ratio would be necessary? Would I need ferrites on the coax when it mates to the 600 ohm line?

    :blink:
     
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  2. EDUK8TR

    EDUK8TR Administrator

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    Greetings Rob!

    I use 600 Ohm ladder line. It is used on a 40m horizontal delta loop. The ladder line runs down to a DX Engineering 4:1 current balun that is mounted on the outside of the basement wall with about 12 ft. of RG8 to a tuner to keep the rig happy with a 50 Ohm load. Advantages-low loss(as long as you keep the coax run less than 15-20ft, any thing above that then losses in the coax go up), Multi-band use with a tuner. There is a discussion herehttp://www.eham.net/ehamforum/smf/index.php/topic,69646.0.html
    regarding ladder line length.

    Hope this helps!

    Wayne C
     
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  3. office888

    office888 Active Member

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    Here's the advantage.

    Db loss / 100ft:
    1 mhz : 0.019 dB
    30 mhz : 0.107 dB
    100 mhz : 0.2 dB
    500 mhz : 0.474

    TMS LMR400
    1 : 0.12 dB
    30 : 0.667 dB
    100 : 1.232 dB
    500 : 2.841 dB

    200 ft of 600 ohm Ladder Line, 16GA Stranded, 100% copper = $136 shipped
    200 ft of TMS LMR-400 = $219 shipped

    I'll be using ladder line for my 10-80 or 10-160 dipole (we'll see if I can "borrow" my neighbor's tree!)

    -Richard-
     
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  4. W5LZ

    W5LZ Crotchety Old Bastard

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    Having only used 450 ohm ladder line, I can' say from experience if there's any advantages to using 600 ohms ladder line. I can say that if I have a choice in the matter, I'd much rather use ladder line than coax, it's just not as 'picky' about getting 'upset' if the SWR isn't very good. I've messed up coax before, harmed it, but have never destroyed any ladder line with RF yet (did run over some with the @#$ lawn mower, but that doesn't count).
    What length? That depends. I use a very good tuner and don't worry much about the length. If I find a band that I/you can't get to tune very well, I/you can always adjust the length a couple of feet and 'cure' that. It's also possible to just use a balun and a particular length for any single band use, and end up with a close to 50 ohm input impedance. If you plan to use that antenna on multiple bands, get a good tuner, makes things much easier. (No, tuners don't mean any more losses than any other means of impedance matching, less in most cases.)
    Ladder line means learning different ways of handling things than with coax. Can't run it just anywhere, or coil it up, or lay it on the ground. It's certainly not impossible to use, but it is different.
    I like the stuff. Don't have to worry about SWR like with coax, it's awful hard to damage with RF, and can make a difference in performance in some cases. (And it's cheap!)
    - 'Doc
     
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  5. Robb

    Robb Yup

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    Is the only advantage less 'line loss'?
    Does it have anything else to offer to bandwidth, sensitivity, etc?
     
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  6. Beetle

    Beetle Well-Known Member

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    Bandwidth isn't really a factor; you WILL have to use a matching network, and I'd recommend a manual one, especially if you're going to be running any amount of power - say 500 watts or more.

    As for a balun...you won't need one if you're running the parallel line all the way to the matching network (assuming it's really a balanced network, as it should be). If you're running 50 ohm coax from the shack to the outside and then going with a balun and parallel line the rest of the way, I'd start with a 1:1 current balun. At some points, the feedpoint impedance may be well below 50 ohms, and a 4:1 will reduce it even further, such as a 20 ohm impedance transformed to 20/4, or just 5 ohms. Your tuner will be carrying more current than it can handle, possibly with a predictable outcome.

    Not sure what you mean by "sensitivity". That's a receiver function.

    And as far as line loss, that info that Richard posted only indicates loss for x feet of coax at a 1:1 SWR, or zero reflected power. With an 80 meter dipole being fed RF at 7 MHz (as an example), the SWR will easily be 10:1 or even worse. This is where the parallel line shines: even at 10:1 (or 30:1), your RF will be radiated and not wasted heating up a piece of coax.
     
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  7. Robb

    Robb Yup

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    Not going to run power at this point; as I want to get this all one step at a time. I have an MFJ-993B Intellituner rated @300W. Or do I have to start at ground zero and get another/different one?

    As in the 'ugly balun'; just a choke to keep RF out of the shack? I would still need to have some coax into the shack, and keep the RF out - right? Or lotsa ferrite on the coax just after it hooks to the ladder line? How would this be best accomplished? I figure that I will have a need of about 90 ft from the dipole itself into my shack/tuner.

    AS in the db losses affecting what the receiver gets. I would rather get more signal into my receiver...even if its just a couple of db's...

    In particular, it is a Alpha Delta DX-CC that I am looking in to. Mole recommended it to me, as I am planning to use it with the Navy MARS program if I get some more study in. Reading all of the time; some of this isn't intuitive and needs more detail.
    http://www.alphadeltacom.com/dxcc_ii.htm
    http://www.wb0w.com/alphadelta/ad_antennas.htm
     
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  8. Beetle

    Beetle Well-Known Member

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    Okay, NOW you tell me it's a commercial multiband antenna! I thought when you said you were putting up a "dipole" it was just that: a plain, homebrew dipole fed with 600 ohm line. I believe the A-D line are multiband, like fan dipoles. They're heavy and they're optimized for the amateur bands. You might find MARS frequencies difficult to tune, if following the manufacturer's instructions.

    Why not build a doublet, as long as you can make it, center fed with that 600 ohm line? It'll be a heckuva lot cheaper, lighter and less visible (also less wind load). I'd sure do that, given the choice.
     
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  9. W5LZ

    W5LZ Crotchety Old Bastard

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    This is just a bunch of random things about using ladder line. No particular order to it, just as it comes to mind. It's also not any kind of definitive argument pro/con, every installation is going to be different in some ways, the 'trick' is to figure out how your installation behaves and the use that behavior to your advantage. Sometimes using ladder line isn't the 'best' way of filling your requirements because of how/where you can put an antenna.

    First, ladder line, of any impedance, isn't a cure-all. It is less susceptible to damage than coax cable is to standing waves. That's because SWR can produce some really high voltages/currents. While the feed line may not be the limiting factor, other parts of the antenna system can certainly be. One of those parts of the antenna system is the tuner typically used. The physically larger tuners usually have larger components (variable capacitors) which can withstand those higher voltages/currents better than smaller tuners and their components. Wider spaced coils in the inductor(s) mean higher ratings too. So, if it's a 'smallish' tuner, don't expect a lot of power handling at all.
    [Tuners are typically rated using Pep rather than AVG power levels. Figure half of the advertised ratings as what you can usually expect it to 'do'. Manual tuners can typically handle larger variations than the auto-tuners. The automatic tuners are only the 'best' when judging that 'best' by convenience.]
    Weather does affect ladder line! The characteristic impedance (any size ladder line) will change when it get's wet, covered with snow/dust/dirt/etc, so expect things to change occasionally. Keeping notes on the tuner settings is a handy guide to keeping things tuned. 'Windowed' line is more susceptible to those changes than 'open-wire' type lines, there's just more area to get covered with stuff. The 'open-wire' type parallel feed lines are more prone to 'swarming' on you. Less structural surfaces that tend to keep things from snarling so much. Any ladder/open-wire line will 'swarm to some extent, so just be more careful with it. It's a factor, but not a huge one (until you have to untangle all that @#$%.
    Unlike coax feed line, ladder line can't be laid on stuff. Keeping it 3 - 5 times it's width away from metal is a good idea. That's usually something like 4 - 6 inches for typical 1" ladder line, closer to two feet for 600 ohm stuff (4 - 5" wide?). As long as it's kept away from stuff ladder line isn't affected a lot. If/when you run it through something to get it inside the shack it will have 'lumps' of impedance changes. Those 'lumps' are typically not a biggy, a tuner should be able to 'smooth' them out with not problem if they are kept to a minimum.
    Using a balun ('remote balun'?) to change to coax to get the stuff to the tuner/radio is the 'weak' point when doing that. The coax used has to be the 'best' you can find, there will certainly be some compromises with that. Keeping that coax as short as possible is a very good idea. If used on multiple bands, the impedance transformation ratio of a balun is -only- a guess, what will be required will change from band to band. It will never stay the same for all bands.
    Be prepared to do a lot of soldered connections! I'm not aware of any connectors that are available and that work well with ladder lines. Not really a big deal, but be aware of it.
    Anything that has a 'flat' surface is going to wiggle in the wind. One trick to using longer runs of ladder line is to twist it, make it into a spiral looking thingy. That lessens the amount of movement from wind. (Ever wonder why those 'tape' advertising thingys are usually in a spiral? Now you know.)
    Can you make 'bends' with ladder line, make it bend around things? Yes. But keep those bends small, never a sharp bend to change it's direction. Hang it with nylon/synthetic/non-conductive cord, or held up off of a wooden 'T', or something.
    There are more 'trick', look at all the installations you can find, see how they do things, then adapt those 'things' to your situation when you can.

    Having been part of MARS for a long time (was, not at present), I found that retuning an antenna to the MARS frequency then 'making do' on the ham bands was my best way of going about it. Just a matter of priority, and that's up to you. There's more work to it than you see at first glance, but it is very rewarding.
    Have fun!
    - 'Doc
     
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  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Here is my antenna setup Robb. It is configured as an inverted VEE type with each leg about 65 feet or so long. As you can see it is a simple hook-up from feedline to antenna. The balun/choke is homemade and consists of "a bunch of turns" of #12 house wire on a plastic pipe form. I used green and white wires just to keep it easier to ID the ends. It was originally configured as a 4:1 but the impedance was much to low on 80 and 160m ( something like 2 or 3 ohms at the shack) so I rewired it for 1:1 and things are much happier. Basically the 450 ohm ladder line connects to one end of the choke across the green and white wires and the coax connects across the other end. The choke is in my basement directly beneath my shack with about 10 feet of Belden 8214 up to the shack. I use either a Ten-Tec 228 manual tuner or a Kenwood AT-230 manual tuner depending with radio I am using.

    [​IMG]





    [​IMG]
     
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  11. Moleculo

    Moleculo Administrator Staff Member

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    The reason for the recommendation of the Alpha Delta DX-CC (or some homebrewed variation of it) was that he mentioned that he has space limitations and getting up a full sized doublet for 75 meters was going to be a challenge. You could feed something like that with either coax or ladder line and it will work fine. Because that antenna is really a fan dipole, you have elements cut for 10, 20, 40, & 75/80 meters. When tuned properly, you won't experience very much loss due to high SWR on any of those bands when using coax. Most of the MARS frequencies that you will use won't be that far out of those bands, so you should still be fine with coax. If you use ladder line, you will have a lot more flexibility with tuning other bands like 60 meters, and others that can be used with MARS. To me, it really comes down to your installation requirements and whether or not you can make the run of ladder line within all of the restrictions that 'Doc gave you. If you can do it, use the ladder line. If the installation gets to be a headache and you don't want to deal with feedline issues, use coax.
     
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  12. Robb

    Robb Yup

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    Thanks all for the info. It has given me some directions to study more about what is happening with the dynamics of wire-fed dipoles. Still need to understand more.

    I will probably go the route that Mole suggested - using coax on the Alpha Delta DX-CC fan dipole. I wanted to steer away from coax, as running it some 80 ft at an angle to my radio shack might over-stress the connector on the end and tear it off. I'm trying to get as much right as I can - before I get the antenna, the fiberglass 35 ft mast, 1:1 current balun, and the coax purchased and set up.

    Any more thoughts and help would surely be appreciated.
    I intend to set the antenna up as an inverted "V" diagonally above a 1-story ranch-type home - 35 ft from the feedpoint to the surface of the 10 ft high roof. Or 45 from the apex to the surface of the ground - same thing - right? (NW to SE orientation) The dimensions of the roof are 60 ft x 25 ft...
     
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  13. Moleculo

    Moleculo Administrator Staff Member

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    Do you have any reasons why you cannot use the ladder line? With a fiberglass mast, you can even just tape the stuff to it, then run it at an angle down to where you're going to run it into the house...
     
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  14. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Put a loop in the cable and anchor the loop thus taking the stress off the connector.
     
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  15. W5LZ

    W5LZ Crotchety Old Bastard

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    Or, if using coax, just bury the stuff. No strain, except for the burying part, then it's just your back. Having it in dirt should even help with some RFI/CMCs.
    - 'Doc
     
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