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ladder line transition to Coax cable help needed.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF6NFW, Jun 23, 2012.

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  1. KF6NFW

    KF6NFW Ham Member QRZ Page

    OK back at this again after dropping to the ground last week and being rushed to ER by code. The heart and I had a disagreement this last week, it wanted to stop, and I didnt, it nearly won.

    anyways, I have 100 feet of coax, and another 100 feet of 450 ohm ladderline now. I can not run ladderline all the way to radio and tuner, as I have to come a ways into the house, more to the center of the house. Nto going to go knocking holes into a wall of a rental either. So I figured I am stuck at this point with Ladderline down from the antenna to the building, and then will have to switch over to coax. What is the proper way to do this.

    I am more interested in knowing if I will need a balun in the system,(I have to build one if so). I am having to relocate the radio shack do to health reasons, i can no longer opperate exclusively alone, or to far from being monitored from the wife.

    My plan was to just drop the coax at the entrence of building and directly connect to ladderline, probably by soldering the two cables together instead of messing with a terminated connection,(just to reduce work and losses)

    someone please shed light on this poor soul!
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Glad to hear you're home and recovering.
    The question of how to interface ladderline with coax can be as simple as just hooking the coax up to the ladderline but this depends on the antenna and the length of the ladderline. All this require a bit of math and the use of a Smith Chart. This can be a challenge since most of us don't use Smith Charts everyday. The original G5RV antennas didn't use a balun and they were connected directly to the ladderline or twin lead.
    That's just an example and may not be right for your purposes. Most connections like that are now done with a 1:1 current balun. Some folks report good results with the 4:1 balun. In both cases you would need the assistance of an antenna tuner to obtain multi-band operation.
    For a single band operation refer to the G5RV and follow the dimensions carefully. Do not deviate from the type of feedline coming from the antenna. The G5RV is just like any other antenna in that it's scalable. Just take the usual frequency a G5RV would be tuned for, this is usually 20 meters, and find the dividing ratio for the frequency you desire. As an example the G5RV is tuned for about 14.150Mhz and you want to build one for 40 meters at 7.150Mhz. Right away you can see there is about a 2:1 ratio but it's not exactly that, so it comes out to about 1.97 times the 14.15Mhz dimensions. There you have it just multiply by 1.97 on the length of the antenna and the lenght of the feedline to the coax junction. Multiply by 2 would probably make for a workable antenna as well. Just remember to use the ratios between the dimensions. If the frequncy is higher then your multiplying ratio would always be less than 1 and if it is lower in frequency then the multiplier would always be greater than 1.
    Now you could also use the length of the antenna feedline as a method of matching to your coax. A simple dipole has about 70-75 ohms of radiation resistance it can be lower if your mounted closer to the ground. If you feed the center of the dipole with 450 ohm ladderline then for every 1/2 wave lenght the radiation resistance of the antenna will be the same as at the center of the dipole and that is the norminal 70-75 ohms which is a good match for 50 ohm coax. The length of the 450 ohm line is determined by the following formula; length =246/Mhz*VF. This is where you divide the frequency in Mhz into 246 and then multiply that value by the velocity factor of the feedline and that will be your length.
    If you can look at W5DXP's website and you will see multi-band antennas with a tuning capability by just varying the feedline length. Look here for details;
    There is also a short section on the G5RV;
    If you want some reading material here's a complete book on antennas;
    It's 625 pages long so you're not going to read it in one sitting. Save it to your computer and refer to it whenever you need some information on antennas and feedlines.
    Hope this helps and it's not TMI.
  3. KF6NFW

    KF6NFW Ham Member QRZ Page

    Thank you for the well wishes and the help with the antenna. I figured there was some math involved, and you are correct about the smith charts, I certainly haven't used one since I learned how many years ago, I don't recall any of it now but the absolute basics of what I am looking at, but in no way a good candidate for teaching it to someone else.

    So If I understand correctly, I can make a half wave 40 meter inverted V at about 40 feet at apex, feed it with ladderline, and then do an ugly balun (1:1) at that junction. so with that in mind, it was my understanding that, switching to coax is not really that great as I would lose a bit in the coax. I just simply wish to be as unnoticed as possible for HF, as I have permission for the antenna from landlord, but it has to be low visibility so no beams here, I figured I would build the antenna in a set of the guying system, as it is all done with Dacron.

    I will read and study this, I dont have anything else to do but stare at the walls and wish i was on the air! I wont likely be on air even for Field day, which mond you is a big deal for me, especialy now that I am disabled and learning to accept that much. still to young to be dealing with a defective heart, hell I havent even made it out of my 30's.
    anyways. it sounds like length is critical, i was hoping it wasnt. but as with everything else in the last 15 years I have been license, I have some learning to do, and enjoy it.

    If I could run ladder-line all the way to the auto tuner, would this be better? I would much rather do that anyways, as I didnt want to use coax on HF.

    I have also been thinking on a fan dipole, but I would feed that with coax as it is a resonant antenna system.

    I am losing my memory slowly so please excuse me, if I seem a bit dumber some days then others.
  4. KF6NFW

    KF6NFW Ham Member QRZ Page

    also keep in mind, I only have a yard 68 feet long and 20 feet wide to work with. it has to be an inverted V because I also have powerlines that cross a corner of the yard.
  5. N0AZZ

    N0AZZ Premium Subscriber QRZ Page

    You would be much better off using low loss coax for the full run and not have the problems with the ladder line like weather. Good coax any more is as good or better than ladder line as far as loss, I have an Inverted V also with a balun and fed with LMR-400 you can check the loss and see what I mean.
  6. G3TXQ

    G3TXQ Ham Member QRZ Page

    Feedline losses for a 50ft run feeding a 40m Inverted-V on 20m:
    LMR400: 6.1dB
    Wireman 554 ladderline: 0.8dB

    To KF6NFW: Keep the coax run to the shortest length possible and use the lowest loss type you can; put a ferrite-cored 1:1 current balun at the transition - an ugly balun is not suitable for this application.

    Steve G3TXQ
  7. KF6NFW

    KF6NFW Ham Member QRZ Page

    That is what I was looking for, I do aapreciate the math as well, as I was using that through the night to come up with a variety of different methods, but the simpelist and most reasonable is to use as little to no coax as possible.

    I may go as far as to locate the tuner near the windo more and just use ladder-line to it, and coax to the rig from there, the difference is about 25 feet shorter this way for a cable run.

    It makes more since to me to do this then to try and run coax through the house, as is, i already have to worry about the coax getting crushed by little people feet that dont look where they walk.

    Setting a station up on an interior wall may not always be the best location! Thankfully I have a wife that is 1) a ham also, 2) tolerable that I am much more involved then she is, and use the radio more for sanity, or lack there of some days!

    I may also just move the station to an exterior wall and use still ladder-line to tuner and then use coax to radio, but keep the coax run to under a couple feet if possible.

    As for the difference to ladder-line and coax, it IS the world of difference. I used Coax last year on a wire antenna, and while it did work and got me on the air, I found that I did more heating of the coax then I did sending it to the antenna. I was able to operate 40-10meters, but not efficiently. I would like to drop the power to about 10-25watts on the TS-520, and still have something reach the antenna.

    The coax I have here is brand new RG-58 from Universal radio, suitable for HF true, efflorescent, not so much! unless. I had to use resonant antennas. I don't have the ground to erect multiple antennas effectively, so I make do with what I do have.

    thanks again for the help, and I looked up several 1:1 designs, and I will home-brew one, I have a couple of Torrids, though I dont remember how to read them or check them, though I dont understand them fully either.

    Thanks again.

  8. KF6NFW

    KF6NFW Ham Member QRZ Page

    I have been licensed since 1997, not very long I agree, but I don't think I have ever heard anyone truly recommend coax all the way. I have only been a General for a little over a year now, and still trying to just make more since of some things, but coax cable I think takes the cake for things not to do!
    It will work as you have discovered, but not well, and probably not to good on the radio you use!
    I did a lot of reading and experimenting before I got to this point. I was asked earlier as well as to why only a 2 inch spacing on home brewed ladder-line, so I checked further into the question, and found that 600 ohm was likely to be even more efficient then the 450 ladder-line, but none the less works much better then 50ohm Coax cable every-time.

    What do you know, this kid can still learn something new! Thanks guys, I do have have a future.
  9. G3TXQ

    G3TXQ Ham Member QRZ Page

    That's a better option that transitioning directly from ladderline to coax; even a short run of coax can have significant losses at the high SWRs involved when you use the dipole as a multiband antenna. You would still need a balun between the ladderline and the tuner if the tuner is unbalanced.

    Worst case - probably when using the 40m dipole on 20m - the SWR on the coax at the feedpoint is around 110:1 whereas with the ladderline it is 15:1; that's why the losses in the coax are so much higher.

    I have some 1:1 designs on my web site:

    The 11th entry in the chart - 11 turns on two stacked FT240-52 cores looks a good choice for 40m thru 10m. In this application you are not interested in preserving impedance through the choke so you can wind it with a bifilar pair rather than RG58.

    Good luck,
    Steve G3TXQ
  10. KF6NFW

    KF6NFW Ham Member QRZ Page

    Thnk you again, I think your site may have been where I saw a good design, other then I saw you used two when others used 1 Torrid, but otherwise was same turn count though others looked as if they were using 2213.

    I will likely just move whole station to the otherside of the room then in Garage, and install air conditioner there then, and operate in comfort without crowding family. it is in Garage now, and was great all through winter, I just turned on a little foot heater to keep me from freezeing, but otherwise, I found that all of my toys like it around 25-35 degrees F. I had a major scare this last week, and has caused us to reconsider where I put things for use, as I may not always be in best environment for health. anyways, I carpeted the garage and did all sorts of cleaning up and making it functional there, but has a huge window that has always been a security concern as why is there a large slider window in my garage, facing the street. True to get to the window you have to get in yard but a 4 foot fence wont stop anyone, so I have installed cameras on that side of life, and also a couple other nice things to scare the crap out of some dumb ass thinking they will be successful. Lasers and noise are good for scaring people!

    So looks like I will flip the shack over, and do that then, as this was my original desire, but never had the ability to get stuff moved to do it, now that I am more and more disabled each day( Cardiomyapathy, and possible MS on top). ok, time to clean the shack again, and turn it around, i guess i will just cover and close that window, and then use the open part to feed cables in.

    Thanks again.

    The math behind it helps alot, and so does the walking through a couple things guys, good job and thanks.

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