Your thoughts: Clip-on attachment to make 40m vert into 80m

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0EYJ, Jan 18, 2020.

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  1. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    I never really work 80m becuase my antennas are too short for it. I've got limited space on my roof.

    What I'm wanting to do is add a clip-on wire to the lower leg of a ladder-line fed doublet, and work on 80m.

    Currently, it's a 33 ft x 33ft doublet with one leg going straight up a 13m high fiberglass pole (I added a thin fiberglass extension to a 12m spiderbeam HD pole). I'm about 5 stories up with this antenna.

    I can tune it with the ladder line, which goes all of the way to the shack. I'm wondering about how long I should make this clip-on leg, so I can work 80m when I want to. I realize clipping it on the low leg, which is horizontal, is less desirable, but I can't get up to the other leg to do it, being that it's so high. :)

    How long would I make the lower leg to have something that tunes, and will work at least semi-well on 80m? I'd end up with some sort of OCF dipole that is an L-shape vertical with one leg going up, and the other snaking a leg around probably 2 corners of a roof.

    You can see the vertical pole in this pic (it's an old pic which has a different vertical dipole on it, but location is same).

    Another thought would be to build a coil I could clip on and off, at the base where it feeds, but would that work well given that my lower wire is much shorter?

    [​IMG]
     
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    What about base feeding & using a length of the ladder line as linear loading. You would need a counterpoise & possibly a LC tuning network.
    A couple relays could switch on the loading network & disconnect/short the ladder line at the right point.

    Ed
     
  3. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    Is that something I could add to my current antenna easily? I'm just looking to have one wire on 1 clip that I can walk up onto the roof and attach by hand.

    Not sure what you mean by using a length of ladder line for linear loading? Do you mean to short one end and basically turn it into a half-length leg that is double in electrical length?
     
  4. WA4SIX

    WA4SIX Ham Member QRZ Page

    OK, the ladder line feeds in the middle, right? If you interrupt & short it at the right spot (Experiment) it would be similar to adding length to a vertical monopole, if you fed it at the bottom. Feed at the bottom with coax & add a radial or two. You might need a tapped coil or a coil/capacitor set at the feedpoint.
    With the assumption that the roof is a ferro concrete makeup, 1+ radials should couple well as a ground plane.

    Ed
     
  5. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    Ok... got it... but curious if I can easily just clip a wire of a certain length onto the bottom radial and get something that will work OK without a lot of effort? I won't be DX-ing on 80m -- our portion of the 80m band in Korea is AWFUL. It's pretty much all NVIS talking locally. We're not allowed anywhere good, from what I can gather.
     
  6. WA4SIX

    WA4SIX Ham Member QRZ Page

    |
    |
    |
    ========| ======>
    |
    |
    |-@()
    --------------------------
    |___________________________

    "|" are existing dipole.
    "=" are existing ladder line as linear loading. "|" at middle of ladder line is relay to short ladder line connected to dipole & disconnect ladder line to shack.
    '@" is coil
    "()" is capacitor
    "------" is coax to shack.
    "______" is radials or counterpoise.

    Ed
     
    W1TRY likes this.
  7. WA4SIX

    WA4SIX Ham Member QRZ Page

    I am sure that your idea may work, but will be rather short & unblalnced. It will need a lot of inductor in the tuner to work.

    Ed
     
    AK5B likes this.
  8. KI8DJ

    KI8DJ Ham Member QRZ Page

    What you could do is short the ladder line at the tuner and load it up as Vertical with end feed.
     
  9. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    I really don't appreciate making fun of me with phallic diagrams...

    (Hahaha... just kidding)

    Thanks... that's an interesting idea. I get it. Maybe it's something I could play with one day, when it's warmer. I like it... thanks for giving me something to do one day. :)


    Here's a thought... I've put a full 40m loop (actually a bit more than 40m, likely) fed with ladder line on this roof. I have thought about putting up the same thing, but cut so that it's basically an 80m 1/2 wave dipole with bent ends in the shape of a rectangle. Question would be... I wonder if I could tune it to 40m or not or if I would end up with a lot of inductance, again?

    Ahh... I think I can make a fan dipole out of this just by keeping what I've got for 40m, and adding two legs to make an 80m dipole part of it...
     
    Last edited: Jan 18, 2020
  10. KC2ZFA

    KC2ZFA Ham Member QRZ Page

    AK5B likes this.

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