Question about homebrew coil loaded dipole...

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K8RJL, Mar 3, 2013.

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  1. K8RJL

    K8RJL Ham Member QRZ Page

    I'm following AG4RQ's plans for a coil loaded 40-10 dipole. The antenna is made from 66' of #18 wire, 33' on each side with 27' of that wound into a coil on each end. It says to use 450 Ohm ladder line from the feedpoint all the way to the tuner. I don't have any ladder line at the moment, I only have 300 Ohm insulated TV twin lead or 50 ohm coax to feed it. My tuner is built into the my radio which is a Kenwood TS-590. Is it possible to use my twin lead or coax to feed it and what alterations would I need to do? I am still trying to understand antenna theory so all info is welcome.


  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Not familiar with that antenna, but I don't know how a 66' long dipole with coils at the ends would match on 40 through 10 meters.

    In any case, twin lead should work about as well as 450 Ohm balanced line, assuming you have a good balun to use between the rig and the twin lead. I would not expect it to work by just plugging twin lead into the coax connector on the TS-590S.

    Actually, even with a good balun, I have no idea if the automatic tuner in the 590S would match this; many "multiband dipole" designs require a wide-range tuner that can handle a huge mismatch, and the auto-tuners built into rigs usually cannot.

    BTW if you want to stick with the original design, 450 Ohm ladder line is pretty cheap and readily available from many sources. The RF Connection sells it cheaply in cut lengths.
  3. K8RJL

    K8RJL Ham Member QRZ Page

    Thanks for the reply and information. Very helpful. The tuner in the 590 says it will do 10:1 tuning which seems pretty good compared to other radios that only do up to 3:1 or so. I'll just order up some ladder line and do it the way it says and see how it works.

  4. KO6WB

    KO6WB Premium Subscriber QRZ Page

    You can make your own feed line with just some wire and something insulated to keep them apart at equal distance. Do not place the balanced feed line anywhere near other objects especially metal. The balanced line would need a balun to properly connect to the TS-590S.
    The TS-590S internal ATU will effectively tune a 10:1 SWR down to an acceptable range for the rig to work into the load. I have this working at my new home. At first I just shoved a copper pipe into a small citrus tree in the backyard and laid a few radials down. The 10 foot long antenna tuned 30 meters - 6 meters. Performance wasn't something to get excited about but it did put out a signal. I worked PSK31 for the first time with it at 25-35 watts.
    The antenna has been slightly improved by using a 14 foot aluminum ladder. This setup manages to tune 60-10 meters. Still, performance is as expected, not that great. The saying here on the Zed is that any antenna is infinitely better then no antenna.
    You should be running through a few more designs before you finally settle on the ones you like the best. It's an experimental experience.
    Have fun
  5. N1SP

    N1SP Premium Subscriber QRZ Page

    Antenna sounds interesting, and I agree with advice from the previous responders but wanted to add a few more points without getting way out there. I use a 66' full length doublet (center fed dipole fed with balanced line) for all my HF 40 mtr and above- have great results feeding with 450 ohm "window line". This antenna is described on the late W4RNL web site. I agree that most any balanced line will work no matter what the impedance. Reason is that any antenna will present different impedance at it's feed point (center of dipole) at different frequencies. Where a 66 ft dipole might have be 75 ohms on 40 meters where it is one half wave- when it approaches being two half waves on 20 mtrs which is the worse case scenario- well over 500 ohms! Feed this with coax, and your loses would be tremendous- thus the beauty of balanced line, very low loss. Now, a balun is also not a perfect situation... can burn off energy as heat when it is a bad match as well- do you use a 1:1 or 4:1 or 6:1? Again, will vary between bands and you will have to experiment to find where the rig is happy on all bands. Most important advise I can give... make sure your feedline, no matter what it is, is not a quarter wavelength or multiple thereof of any band you plan to operate- more info on this (and length charts) in ARRL handbook and antenna book. 73, Randy N1SP
  6. K8RJL

    K8RJL Ham Member QRZ Page

    Yeah I am trying all sorts of arrangements here in and around my condo to find something that works. Next up is building a magnetic loop although that will take some time and research. I'm also looking for a place to string up some stealth #24 or 26 wire around the exterior of the condo that they won't notice when doing the landscaping here. Someone is always on the roof here cleaning the gutters or trimming trees so I need to find the perfect spot.
  7. OH2GUF

    OH2GUF Ham Member QRZ Page

    I use 36 feet center fed trap dipole, with 450 ohm ladder line. I have MFJ-971 tuner ,that has balanced feeders(a 4:1 toroid balun is built in for balanced line). It works well on high bands,especially 17 meter band. Have worked with that most of Europe. My rig is old Kenwood TS-870S.
  8. AA7EJ

    AA7EJ Ham Member QRZ Page

    Rob, be aware that you can get 450 Ohms ladder line of basically two flawors - stranded CU or copper clad steel. Some sellers do not tell you that up front.
    Electrically same, but IMHO copper clad steel is a chalenge to work with.
    73 Vaclav
  9. K0RGR

    K0RGR Premium Subscriber QRZ Page

    You might want to feed the 450 (or 300) ohm line through a 1:1 balun - it will make the connection neater than just splicing it to coax, and will preserve the balance in the feedline. This antenna looks like it's supposed to be resonant on 40 and non-resonant on the higher bands. Let us know how it works.
  10. K8RJL

    K8RJL Ham Member QRZ Page

    Thanks for the tips guys. I have the coils built so far. Going to order the ladder line tonight. Will post back when it's up and running. Probably be end of the week due to work schedule.
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