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How long is your ladder line fed dipole?

Discussion in 'Survey Center' started by W8JI, Jun 24, 2010.

?

How long is your balanced dipole antenna on the lowest band you use it?

Poll closed Jun 29, 2010.
  1. about 88 feet on 80 meters, or 44 feet on 40 meters

    1 vote(s)
    3.7%
  2. about 102 feet on 80 meters, or 52 feet on 40 meters

    6 vote(s)
    22.2%
  3. about a half wave on the lowest band

    19 vote(s)
    70.4%
  4. about 5/8 wave on the lowest band

    1 vote(s)
    3.7%
Multiple votes are allowed.
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  1. W8JI

    W8JI Ham Member QRZ Page

    I am doing a lengthy detailed article on balanced feedlines and baluns that includes actual measurement of baluns and antenna systems for balance and common mode currents, as well as balun losses.

    Because I want to make this article as useful as possible, and because feedline length and antenna length are important to balun and tuner performance, I would like to learn how long most antennas are.

    I know there are some who say "as long as it can be", but that is electrically not a good idea because impedances at the feedline could range from ten's of ohms to several thousand ohms.

    This survey is about antenna length in a balanced system.
     
  2. AI3V

    AI3V Ham Member QRZ Page

    I do thing one of 2 ways:

    1- Just like Mr. Hertz did- exactly 1/2 wavelength.

    2- Sometimes I can't be bothered to dig up the tape measure, my "40M" Hertz stretches EXACTLY from the chimminey to the poplar tree.:cool:

    I can detect NO difference in actual performance between the 2 methods. With or without a balun (of ANY ratio installed).

    The wonderful thing about baluns, is they do almost nothing for you, and by the same token, they almost never do anything against you either. They are a very forgiving device to be randomly buying and installing.

    When operating on frequency’s other than the fundamental resonant frequency, since I usually have just about zero control of where the supports are- and therefore very little control of the radiation pattern- Then "as long as possible" is my rule.

    Of course I have use surveyor's techniques to set antenna supports for Military relay work, I had a somewhat larger budget, and a bit more land available than most stations.

    Be sure to include details on how well a balun works when operated in a even harmonic Hertz that has been unbalanced by nearby objects, like the wiring in the house under it. This would be a far more typical installation of a amateur antenna.:D

    It would also be instructive to the new guys if you measured the common mode on feedlines that are not symmetrical in the antenna field, this will show how easy it is to negate any balun installed.

    73's

    Rege
     
  3. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    I now only need a dipole on 80 and there I've found that the easiest to work with is a 130 ft or half wave doublet.

    On 40 & up, I've done well with shorter dipoles down to about a 52 fter.
     
  4. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    I can't accurately answer your poll Charles since my antenna doesn't quite fit the options. I guess it is close to a a half wavelength on 40 meters.

    My antenna is 70 feet long (35 feet each leg), is installed in the attic, and is fed with 300 ohm ladder line. The tuner is a Johnson Matchbox, I know you dislike them but it really does an excellent job for my installation.

    I made the antenna just a little longer than a half wave on 40 to avoid high impedance problems on 20 meters and it works. It operates on 40, 20, 15, 12 (works using the 10 meter setting), and 10 meters but will not load on 30 meters at all. I have a seperate dipole for 17 meters.

    I don't have any RF feedback problems and since my shack is on the second story I don't have a ground other than the AC grounding recepticle. I can actually load up on 75 meters but the efficiency is poor and I suspect the tuner is claiming more power than the antenna so I don't operate that band. I also don't run more than 100 watts since more power could be bad news with an indoor antenna.:D
     
  5. PA1ZP

    PA1ZP Ham Member QRZ Page

    Hi Everybody

    My Rotary homebrew V-dipole is 2 x 6 mtrs abt 2 x 19 feet.
    this V-dipole can be extended to 2 x 22 feet is 2 x 7mtrs
    Ladderline is homebrew abt 600 Ohm and 13 mtrs long (41 Feet)
    Antenne hight 11 mtrs 34 feet at feedingpoint and 14 mtrs or 44 feet at end tips

    Use this V-dipole for 10 t/m 40 mtrs . and 80 mtrs RX
    use full size vertical on 80 mtrs TX
    Tuner is homebrew S-match of PA0FRI design.
    combination is OK for 500 W + (no more power available or alowed here)

    Article abt this V-dipole and radiation patterns and pictures can be found on:

    Article is written in Dutch languge.

    http://blogs.hamstart.net/blog02/archives/1469.

    Very usable antenne for 10, 12, 15, 17, 20, 30, 40 mtr bands.

    SRI use no baluns but feed directly into balanced tuner.
    Home brew S-match capable of abt 2 kW

    For S-match design look at:
    http://www.pa0fri.geerligs.com/
    IN ATU part of website.

    Also use balanced lines to make 2 or 3 elements portable vertical fased arrays articles found on same blog as V-dipole article.
    Abt pasing with ladderline see:
    http://blogs.hamstart.net/blog02/archives/33
    We never have seen others do this.
    We use half wave verticals at 1/2 lambda distance of each other and use half lambda ladderline to feed the verticals in or out of phase.
    Very easy in use and changing direction.
    Antennas for 40 mtr get a bit big thoug.

    73 PA1ZP Jos
     
    Last edited: Jun 25, 2010
  6. KA5S

    KA5S Ham Member QRZ Page

    Half-wave at 2.3 MHz. (MARS)


    Cortland
    KA5S
    AAR5UT
     
  7. KE5FRF

    KE5FRF Ham Member QRZ Page

    At the moment I do not have a ladder line fed dipole, only a ladder line fed loop, but when I had my doublet a few years back it was 102 feet long with 300 ohm ladder line to a DX Engineering 1:1 current balun with a short coax jumper through the window to a manual roller inductor tuner. I chose to use the external balun because the built in balun is a 4:1 voltage and I hoped for (and achieved) reasonable all-band performance with low VSWR with the 1:1 balun. On more than one band I was able to bypass the tuner completely because my "conjugate matching" was nearly perfect. I believe the length of my balanced feedline was roughly 80 feet. I was particularly happy with 20 meters and had better performance on that band than I've had with any other antenna. Of course, the previous solar cycle was still reasonably strong.

    Currently I only have the balance fed loop with a remote tuner and the fan style wire vertical with ground radials. Both antennas perform very well on 20, 30, 40, 80, and as far as I can tell on most other bands as well. The vertical is fed with buried LMR400.
     
  8. WS2L

    WS2L Guest

    Thread moved to appropriate forum.
     
  9. AG3Y

    AG3Y Guest

    I once heard 132 feet, and our lot is 150 feet long, so I made it really close to 132 feet. It is fed with ladder line of no particularly selected length ( long enough to reach from center of antenna to the tuner ) and the only coax in the system is the little chunk that goes between the radio and the Matchbox(tm)

    The center is at 35 feet, and the ends are about 8 feet off the ground.

    The Johnson Matchbox is a device I have wanted almost all my ham life, and I finally picked up an almost mint specimen . Signals improved immediately after I made the change from a home-brew G5RV design to a 100% ladder line feed with matchbox system.

    True example, on 40 meters, working DRM on 7.173 ( digital SSTV watering hole ) , I used to get marginal signals to around 1 or 2 stations at a time. Using the new arrangement, I routinely can put a decent signal into around 4 stations at the same time.

    No numbers, but real results, regardless.

    73, hope this info is useful. Jim
     
  10. WA4BRL

    WA4BRL Ham Member QRZ Page

    As long as would fit in the yard, approximately 160 feet. Some would call it a doublet, but it has equal length legs, is balanced, and is indeed a dipole.
     
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