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Inverted L confusion

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by M0IUS, Jan 1, 2019.

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  1. M0IUS

    M0IUS Ham Member QRZ Page

    Hello everybody

    I've planned to put up an inverted L in my garden. I think it's the best I can do for DX without upsetting neighbours.

    I've got enough room for an adeuqate ish radial system and plan to use a tuner at the base.

    I'd like to focus on DX on 20m and 40m, but it would be nice to have a usable antenna on 80m and 160m too if I can.

    My initial plan would be a 70' odd L, about half up and half along, strung over a tree.

    For better access to 160m without affecting the DX performance on 20 and 40, would it be better to just make the wire 125' long, or add a trap?

    thanks!
    Ed
     
  2. M0IUS

    M0IUS Ham Member QRZ Page

    Second question - where I want to ideally put the vertical, there's a pond between the base and where most of my radials need to spread out. Will I suffer much by bunching radials together for the first four or five feet before fanning them out?
     
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    I ran an L on 160 for a while. The up part was ~50ft, and the over part was ~200ft. It worked ok, especially for contacts out to ~1500 miles. It has since been replaced with a 558ft long three-sided loop which is much quieter (SNR) and lets me receive more signals.

    Any ~half-sized coil-loaded antenna for 160m is going to have a very narrow useable bandwidth unless the tuner can stand really high RF voltages...

    I would use a trap to delineate 160m from 80m; not just a "coil".
     
  4. AA5CT

    AA5CT Ham Member QRZ Page

    re: "I'd like to focus on DX on 20m and 40m, but it would be nice to have a usable antenna on 80m and 160m too if I can."

    Have you seen G0CWT's webpages? I have, and still am, using his designs on 160, 80, 60 and 40 meters, *with good* results. I get spots in UK and Europe every night on 160 using WPSR, from the central part of the US. Not everyone can do that.

    Night after night here lately one can compare my results with those of KD6RF who is running more 'conventional' design antennas on 160.
     
  5. M0IUS

    M0IUS Ham Member QRZ Page

    Thanks - his are vertical loops aren't they? If I put one of those up I'd only be able to face it north/south which wouldn't be ideal, I need something very omnidirectional. I can't really do a horizontal loop either.
     
  6. G3YRO

    G3YRO Ham Member QRZ Page

    If you want to use an Inverted L, if I were you I would get (or make) a 40m trap and an 80m trap . . .

    So you put the 40m trap about 33 ft above the ground feedpoint . . . then the 80m trap about 20 ft above that (adjusting the length above the 40m trap to get it resonant on 80m) . . . then you would need another 60ft (roughly) beyong the 80m trap to resonate it on 160m.

    You'd then have a REASONABLE 3 band trapped vertical, resonant on those 3 bands - but it will only work as well as the radial system (especially on 160m, where to make it efficient you'd need over 40 130ft radials !)

    20m is a different issue altogether . . . personally, I think a 16ft vertical mounted at ground level would be a waste of time ! (as it's going to be completely screened by buildings, trees, etc)

    Roger G3YRO
     
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  7. AA5CT

    AA5CT Ham Member QRZ Page

    Yes, Vert. Note: I tried a G0CWT 80m loop horizontal, about 16 ft up, and rx was dead, so, they work BEST vertically.

    re vertical - BUT, unless you're working ground wave, during the day, 12 noon, you're not going to have a problem off the sides. Skywave cures all, it would seem.

    Remember, you're *dead* off the ends of a dipole too (AND no body expresses 'deadly fear' about that). Again, skywave cures that.

    Added: BTW, the 160m QW loop becomes a full WL on 40m, but, I think it works more like a FOLDED DIPOLE when it is 16 ft x 40 ft rect with the top at 22 ft. It works well too using a 4:1 balun. Becomes a FW loop on 20m then too.

    Added 2: If you make just an 80m QW loop, it's 16 ft x 16 ft - a very small footprint (+ guys wires, of course.)
     
    Last edited: Jan 1, 2019
  8. AI3V

    AI3V Ham Member QRZ Page

    All the power you put into a antenna goes somewhere !

    Start with a theoretical quarter wavelength Marconi, with nothing around it.

    It radiates equally well 360 degrees around, and with predictable strength at various vertical angles.

    Now take a more or less random wire, with more or less random things around it, with a more or less random ground system.

    The power may (or may not) be wasted in ground loss.

    The power may (or may not) be wasted in tuner loss.

    The power may (or may not) be wasted by being absorbed by nearby objects.

    The power may (or may not) be wasted by being sent in the wrong direction.

    The power may (or may not) be wasted by being radiated in the wrong elevation.

    About all most stations can do is install some wire, as far away from other things,try and tune it so it's reasonably close to resonance and the same impedance as you transmitter/feedline combination, and hope the signal goes in the direction of the dx.

    Rege

    Edit: but wait! There's more!

    Rx may (or may not :) ) be better or worse in respect to noise pickup depending wether or not there is noise, and just where and what that noise is.
     
    Last edited: Jan 1, 2019
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  9. M0IUS

    M0IUS Ham Member QRZ Page

    Thanks
    I'll bung a bit of wire up and see what happens.
    Radial field us going to have to start a couple of metres from the base bit it will I guess be better than nothing
     
  10. KD6RF

    KD6RF XML Subscriber QRZ Page

    In broad brush terms, around 90 ft (or around 3/16 wavelength) is a practical minimum for efficient operation using an inverted-L or vertical for 160 M.

    Tuner at the base is a good efficient way to go - the issues that arise are encountering extreme impedances that are outside the range (either matching range or voltage breakdown range) of the tuner. Again, around 90 ft is a good number for this and is the length that I use here.


    When geometry is roughly "square" with the the height about the same as the width, it turns out that radiation patterns are good low-angle DX-worthy patterns an all ham bands, even the upper band. Operation on the lower bands is primarily vertical polarization, while on the upper bands the horizontal section radiates like a horizontal dipole at the same height.

    If you are interested in the radiation patterns of either a 23 ft tall x 22 ft wide 80 - 6 M Inverted-L, or a 45 ft tall x 45 ft wide 160 - 10 M inverted-L, here is the data ===>

    80 M - 6 M Inverted-L ===> http://vtenn.com/Blog/?p=110
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    160 M - 10 M Inverted-L ===> http://vtenn.com/Blog/?p=83
    [​IMG]
    [​IMG]


    The particular scheme I developed uses a loading coil for the lowest band and a 9:1 (or 4:1) Unun at the base for the higher bands. This allows for a decent length of coax to be used with the tuner in the shack and low losses in the coax.
     
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