Radial length

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AD5ND, Jan 30, 2011.

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  1. AD5ND

    AD5ND Ham Member QRZ Page

    I want to build a 40 -10mtr multiband wire vertical. I plan to string it up a pine tree. The wire lenght depends upon luck. But will be at least 40' or more. The radials will be 8' off the ground, attached to other trees. I'll use a L match at the feed point. Do I need several radials tuned to each band or make all the radials 1/4wl on 40mtrs?
     
  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Elevated radials, you need at least 2 quarter wave radials for each band.
     
  3. W0BTU

    W0BTU Ham Member QRZ Page

  4. KH6AQ

    KH6AQ Ham Member QRZ Page

    Good advice. One thing to add is a 1:1 current balun at the feedpoint will 'force' most of the return current to take the radials rather than earth ground and up the outside of the coaxial cable to the feedpoint.
     
  5. N0AZZ

    N0AZZ Ham Member QRZ Page

    Just wish my wife would let me put in raised radials for my vertical I would be happy with just 12-18" above ground.
     
  6. W0BTU

    W0BTU Ham Member QRZ Page

    I think if you have a vertical with 2 elevated radials, you don't want to connect it to an earth ground. Just choke the feedline at the feedpoint.

    If you want to know why, do a search at http://forums.qrz.com/search.php?search_type=1 for related posts made by W8JI. He explained it better than I can.
     
    Last edited: Jan 30, 2011
  7. W8JI

    W8JI Ham Member QRZ Page

    If you use enough radials it does not matter if they are elevated or buried. It also does not matter how long they are, so long as they are around 0.2 wave on the lowest band.

    Where radials can get into resonant effects are really just two places:

    1.) When there are only a few radials.

    2.) When the radials are not buried deeply.

    Otherwise, at least according to what I have measured here, radial length doesn't mean much for field strength.

    73 Tom
     
  8. G3TXQ

    G3TXQ Ham Member QRZ Page

    An interesting question - it wasn't obvious to me that resonant radials would be needed for every band, given that you have a matching network at the feedpoint.

    I modelled a 34ft vertical and looked at the difference in signal strength at 10 degrees elevation using just four 34ft radials as opposed to four resonant radials; here are the penalties of using the fixed 34ft non-resonant radials:

    30m: -0.23dB
    20m: 0.9dB
    17m: 1.5dB
    15m: 2.2dB
    10m: 4.2dB

    Steve G3TXQ
     
  9. W5DXP

    W5DXP Ham Member QRZ Page

    Steve, is a negative penalty an improvement? Not trying to be difficult - just trying to parse your data.
     
  10. G3TXQ

    G3TXQ Ham Member QRZ Page

    Cecil,

    Those were the penalties of using the non-resonant radials. So the non-resonant radials were worse on all bands except 30m.

    Apologies I didn't make it clear.

    73,
    Steve G3TXQ
     
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