Trap Antenna with Ladder Line - How to Connect

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AC3DS, Dec 28, 2018.

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  1. AC3DS

    AC3DS Ham Member QRZ Page

    I recently acquired a W9INN trap antenna, new in the box, packaged around 1985. There are three traps on each side of center, with a short run (~18") of ladder line feeding the center. The traps, and the wire itself, have label markings for 10m, 15m, 20m, 40m, 60m, 80m, and 160m. This is my first antenna and I will hopefully be hooking it up to an Icom 7300 in the next week.

    My primary question is this: What are some valid methods for transitioning from the ladder line to 50 ohm RG8u in order to get back to my radio?
     
  2. WZ7U

    WZ7U Ham Member QRZ Page

    4:1 guanella balun?
     
  3. VK3YE

    VK3YE Ham Member QRZ Page

    There are some balun references in the review thread at eHam https://www.eham.net/reviews/detail/4116

    The balun referred to appears to be 1:1 http://www.unadilla.com/products/W2DUseries

    I am surprised that the packaging mentions 60m. That band wasn't available to amateurs back in 1985. Maybe it was just for WWV listening?

    The antenna above will get you on the air on multiple bands but there will be some compromises. If you'd prefer no-compromise performance on a few band then a fan dipole with no traps may be a worthwhile project.
     
    Last edited: Dec 29, 2018
  4. KE6EE

    KE6EE Ham Member QRZ Page

    There should be some instructions with the antenna. Reading the reviews I assume that the antenna requires
    lengths of wire extending down from the main (horizontal) wire in order to provide the proper match on each band.
    As to feeding the antenna with ladder line--this doesn't make much sense to me but the very short length of ladder
    line may not be significant to the performance of the antenna.

    The best approach to understanding this antenna would be to use an antenna analyzer at the ladder line to see
    where the antenna matches on each band (with reference to 50 ohms). A local ham with an
    analyzer would likely be glad to help you out.

    Often dipoles (which are balanced antennas) are fed using (unbalanced) coax via a balun at the feedpoint. This
    is to prevent common mode RF on the coax which would mean that the coax is acting as part of the antenna. That
    can be very problematic: noise, tuning problems, etc.

    Assuming the antenna is well-designed and actually works, I would use a high quality 1:1 current balun at the
    feedpoint which I assume is intended to be at the end of the 18" of ladder line.

    High quality, effective current baluns can be purchased from DX Engineering, Balun Designs or any number of
    other places. Or you can make one by looping your coax through a few toroids. W2DU baluns are not very
    effective.
     
  5. W5DXP

    W5DXP Ham Member QRZ Page

    Did W9INN use ladder line on his trap dipoles or is this your idea?
     
  6. AC3DS

    AC3DS Ham Member QRZ Page

    The ladder line was present upon purchase and is original to the design.

    Unfortunately, there were no directions with the antenna in the box. That being said, I've found directions to other W9INN antennas, just not this one in particular. To be honest, I'm not really sure how to read and interpret these directions. They seem to indicate that it is possible to twist both ends of the ladder line together and solder that to the center of a single wire (RG8U) that goes to the tuner. Can that be correct?

    Here are W9INN directions for a similar antenna:

    https://drive.google.com/file/d/1GB1bqR6KmZdC8XN7TPQNYP-disffnJxf/view?usp=sharing
     
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    No.

    The twisting the lines together etc. are to use it as a top loaded 160m Marconi for 160m only.

    To use it as a dipole on all bands, just use a 1:1 current balun, connect coax, get it up high above ground and use it.

    It will be very narrow band on 80m but on the other bands should cover most of the entire band for each.

    BTW I do not recall any balanced line connected to any of these and I corresponded with W9INN many times over the years back in the 70s and 80s before he unfortunately became SK. If you have a "brand new" W9INN antenna that did not come complete with printed instructions, I suspect it wasn't all that "brand new" and someone else opened it and repackaged it. They all came with printed instructions. I had many of these.
     
  8. WA0YDE

    WA0YDE Ham Member QRZ Page

    I bought one of these years ago at a hamfest. It was used and came with instructions.
    It was the 40-80-160 meter model with loading coils and a center connector for coax.
    Being a loaded dipole, you will need a tuner for full band coverage. I wouldn't bother with using a balun. The real challenge was getting it high enough!
     
  9. W5DXP

    W5DXP Ham Member QRZ Page

    In general, traps and parallel feedline are not usually used together. In general, if one uses traps, one doesn't need ladder line and if one uses ladder line, one doesn't need traps.
     
    WA0YDE and N8AFT like this.

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