If the opposite ends of the dipoles wires are left free and not connected to each other you do not have a cage dipole. The inner capacitance between the wires and the added inductance will cause a problem in tuning and will act more like a regular dipole with distributive capacitance and inductance. A cage dipole is basically like a big fat pipe made out of wire, nothing else. The fatter the diameter of your element, the lower the Q and the wider the bandwidth. But the suggested? way of feeding multiple wire elements in parallel but unterminated at the far end is not a cage dipole and will not act as one.
Chris WB5ITT On Thu, Jan 16, 2020, 5:21 PM Tom Watson via BVARC <bvarc@bvarc.org> wrote: > What would happen if you made the legs of the dipole out of computer > ribbon cable tied together at the feed end and open at the other? Would > that be similar to what you are talking about? > > > > *From:* BVARC [mailto:bvarc-boun...@bvarc.org] *On Behalf Of *Martin > Blaise via BVARC > *Sent:* Thursday, January 16, 2020 4:35 PM > *To:* BRAZOS VALLEY AMATEUR RADIO CLUB > *Cc:* Martin Blaise > *Subject:* Re: [BVARC] Antenna Theory Technical Question > > > > Do not use this kind of fan dipole see attached. > > > > On Thu, Jan 16, 2020 at 1:21 PM Kirk Kendrick via BVARC <bvarc@bvarc.org> > wrote: > > Rick, > > > > Fan dipole with all the wires the same length....and closely spaced. > Resistance should be 2) unchanged as others pointed out. Coupling will > cause broader BW like a cage dipole. Unless your antenna conductors are > manufactured to limit variance.... Impedence in real world will be hard to > model in a bundle that has varying capacitance due to uneven spacing and > varying inductance due to twists and turns within bundle > > > > I'll throw out a slightly different thought. > > > > I think it would also model as a sleeve antenna. That would make the > EZNEC model have only 1 dipole driven and all the other wires evenly spaced > around it potentially with small gap at feed point (that shouldn't be > needed since it's a zero voltage point). > > > > At least, my mental model has them as (close to) equal. But my brain > wanders a bunch. > > > > 73, > > Kirk KK2Z > > > > PS: My favorite "work of art" sleeve dipole in one of the early antenna > compendiums was a vertical made up of a ring of resonators -- one for each > band -- around a driven vertical in center. > > > > From: Rick Hiller <rickhille...@gmail.com> > To: BRAZOS VALLEY AMATEUR RADIO CLUB <bvarc@bvarc.org> > Subject: [BVARC] Antenna Theory Technical Question > Message-ID: > <CABNEQE_mKnBH3if0mmvenpjopxJJf+c-ap=+ > eosvapc+vtd...@mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > I am in the midst of analyzing a Ham market HF antenna. Still building the > EZNEC model, but working it thru the gray matter. > > Case: Take a 1/2 wl dipole antenna -- center fed. Each side is made up of > multiple, equal length wires that are each insulated, parallel, and closely > spaced. The wires are connected/common at the center feed point, but open > at the far end. > > If, at this length, each wire's material DC resistance is 5 ohms....does > using multiple wires in parallel, as described above, 1) lower the total RF > material resistance, as resistors in parallel....or 2) does it stay the > same or 3) does it become additive? > > Any comments would be appreciated. I've got my hypothesis, but wishing > additional input. > > Thanks and 73 ...Rick W5RH > > > > ________________________________________________ > Brazos Valley Amateur Radio Club > Get on the air - 146.94 Repeater > Volunteer now for the Houston Hamfest > > BVARC mailing list > BVARC@bvarc.org > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > > ________________________________________________ > Brazos Valley Amateur Radio Club > Get on the air - 146.94 Repeater > Volunteer now for the Houston Hamfest > > BVARC mailing list > BVARC@bvarc.org > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org >
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