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Parallel Dipoles in the Attic

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WD9DWT, Jun 1, 2021.

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  1. K7KBN

    K7KBN Ham Member QRZ Page

    The 40 meter dipole should be usable just as it is on 15 meters. It's about 3/2 wavelength (an odd number of half wavelengths).
    The 20 meter dipole won't work very well on 20 at all, because it's about 2/2 wavelengths (an even number).
     
    SM0GLD likes this.
  2. K8JD

    K8JD Ham Member QRZ Page

    I would seriously consider having the "parallel" dipoles share a feedpoint and feedline to the rig. I would hook them up and sweep the SWR from below to above the bands and calculate any shift in preferred resonant (or low swr) freq and trim the wires to compensate. I have made some 'fan" Dipoles for 2 bands to take camping and they were easy to trim/tune and check in the back yard before the trips. Since each dipole is made for one band the other antenna will not appear to be part of the system at the other freq. Any stray coupling will be compensated for when you re trim for lowest SWR.
     
    Last edited: Jun 3, 2021
    NE4ME likes this.
  3. NE4ME

    NE4ME Ham Member QRZ Page

    May not be what you want to hear, but you may be best served by a horizontal loop as large as you can make it in the attic and either feed it at a corner or a side and see how it does. I don't have a huge amount of experience with loops only having used a couple of them through the years, but a decent tuner and you should be in business. Compared to your options mentioned so far it can't hurt to try, plus they seem to always be low noise in my experience.
     
  4. SM0GLD

    SM0GLD Ham Member QRZ Page

    Yes and please tell us the result.
     
    WD9DWT likes this.
  5. N3DT

    N3DT Ham Member QRZ Page

    It would be interesting if the 1/4WL with hamstick 40M antenna would couple to the 20M antenna. I don't see why not. I'm not sure you even need to center the coupled antenna on the driven antenna. I would think it would be easy to try. If it worked, then you could also couple another band to it easily on the other side, and then another below it if desired, say 10 and 12M. Then you'd have a 4 band antenna with one piece of coax. And no tuner.
     
    WD9DWT likes this.
  6. WD9DWT

    WD9DWT Ham Member QRZ Page

    Should the coupled dipoles have a terminating resistor between the 1/4WL elements?
     
  7. SM0GLD

    SM0GLD Ham Member QRZ Page

    No, just connect the 1/4 wl sections to make it a 1/2 wl dipole.
     
  8. N3DT

    N3DT Ham Member QRZ Page

    There is no mechanical connection between the fed dipole and a coupled resonator. The CR half wave wire is just that, coupled. I really believe it's worth a try if it's not too much trouble. You could try one at a time. That''s what I did and it was like magically adding bands to the coax. I didn't find the spacing very critical either, within reason. But there's not much you can do about the radiation resistance when it achieves resonance, it is what it is, just like my 80M dipole at 70' it's resonant at 3600 and is 75-j0 so the only way to achieve a better SWR is to make a matching network, but at 1.5:1, it's not worth it. Now when I go to FT8 on 80M I either have to add a bunch of RG11 or you can go here and do a one frequency network. https://www.analog.com/en/design-ce...-tools/rf-impedance-matching-calculator.html#
    Or you can accept the 2.2:1 SWR and not worry about it and use the tuner in your transceiver, which with my TS2000 I find not very effective, I find it's better to just accept the SWR.
     
    WD9DWT likes this.
  9. 2E0VSS

    2E0VSS Ham Member QRZ Page

    Guys,
    Look at the site of XQ6FOD Manfred
    He is a brilliant thinker and his Parallel Dipoles are Inspiring..
    Hes at Ludens.cl (Google translate)

    M
    73
     
    WD9DWT likes this.
  10. WD9DWT

    WD9DWT Ham Member QRZ Page

    Oh, I get it now - it's a single parasitic element.
     

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