Parallel Dipoles in the Attic

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

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  1. KO4PQT

    KO4PQT Ham Member QRZ Page

    I am trying something similar in a small attic. I have two single-band dipoles, 15 and 10 meters, each with their own feed lines. I tried them parallel to each other and was fine on 15 but it threw the 10 meter readings way out of wack. I don't have room to get them at 90 degrees to each other but I got them to about 50-60 degrees to each other and was able to get a minimum SWR of around 1.2 in the middle of each band and under 1.5 across the entirety of both bands.

    I suppose there a lot of variables involved, but just my experience if it helps. Good Luck.
     
    WD9DWT likes this.
  2. SM0GLD

    SM0GLD Ham Member QRZ Page

    I simulated a dipol cut for 7,1MHz. The coax is connected to this dipole to feed all frequencies.
    To this dipol I added two CR, one cut for 14,2MHz and one cut for 28,6MHz.
    Both additional dipoles are placed 1" from the 40m dipole.
    This will work fine as long as you can accept a VSWR of approx 2:1 on the higer frequencies.
    If you increase the distance between driving element and CR the impedance will increase.
     
    WD9DWT likes this.
  3. N3DT

    N3DT Ham Member QRZ Page

    The coupled resonator antennas I use have very good SWR. Mine are spaced about 1.5", I use telco drop wire. The chart in the ARRL book shows about 1.7" for #14 wire. #18 wire would be slightly more, but as I have said, I never found much critical about it within reason. Actually I don't even measure my spacers, I just eyeball them.

    Although my 80M dipole shows 1.5:1 at resonance, the 20M CR shows 1.15 at 14.0, 1.11 at 14,07 and 1.48 at 14.350. Granted, I have almost 200' of 9086 or similar to the antenna. The 17M is 1.43 at the low end and 1.38 at the high end, it's resonance it a bit on the high side but the TS2000 doesn't care at all. Using the tuner even produces less PO on the LP100A.

    My CR's off my 40M dipole are just as good if not better.

    And yes, they can be considered parasitic elements.
     
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  4. SM0GLD

    SM0GLD Ham Member QRZ Page

    Yes, using thicker wire will reduce impedance. In my simulation I went from #12 to #9 and the now VSWR is close to 1,5:1.

    I have used CR for 15m on my OCFD. It was placed at a distance to make it 200 Ohm, abt 6"
    High impedance is easier than low.
     
    WD9DWT likes this.
  5. WD9DWT

    WD9DWT Ham Member QRZ Page

    This is good information. It proves that angling them will minimize the interaction between them, the caveat being that the directivity may not be what you want.
     
  6. AK5B

    AK5B Ham Member QRZ Page

    Exactly why I suggested earlier that he take the 40m hamstick out of the attic altogether and orient it vertically and use a couple of 26 gauge radials. Camouflage and stealth can pay good dividends when properly applied.
     
  7. N3DT

    N3DT Ham Member QRZ Page

    My understanding is he is using the hamstick as one half of his 40M dipole. I would think that would work better than just a hamstick on the deck with a couple radials. But who knows.
     
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  8. WD9DWT

    WD9DWT Ham Member QRZ Page

    Precisely. The intent is that it would provide the efficiency of half of a half-wave dipole while fitting snuggly within the confines of the attic space.
     
  9. AK5B

    AK5B Ham Member QRZ Page

    Hamstick inside an attic... efficient? o_O
     
  10. WD9DWT

    WD9DWT Ham Member QRZ Page

    Thank you for running that simulation. Now the real-world challenge will be to build spacers that are easily adjustable!
     

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