Slightly off-center feed point will make it work on other bands. On Thu, Jul 14, 2022 at 6:24 PM Rick Hiller <[email protected]> wrote:
> Don’t see why not. 3/4 wl long and coil has 3 x Xl of 40 mx. > 3rd band’s free. > RH > > Sent from my i-Thingamajig > > On Jul 14, 2022, at 3:51 PM, Jeff Greer <[email protected]> wrote: > > It might work on 15, too... > ------------------------------ > *From:* BVARC <[email protected]> on behalf of Rick Hiller via > BVARC <[email protected]> > *Sent:* Thursday, July 14, 2022 3:30 PM > *To:* Larry K5LJ <[email protected]> > *Cc:* Rick Hiller <[email protected]>; BRAZOS VALLEY AMATEUR RADIO > CLUB <[email protected]>; TDXS List <[email protected]> > *Subject:* Re: [BVARC] Seeking Antenna Design Info > > Very cool to see a real world example of what I was researching. > Tnx. Larry.....Rick. W5RH > > Sent from my i-Thingamajig > > On Jul 14, 2022, at 2:18 PM, Larry K5LJ <[email protected]> wrote: > > Now and then we all have these “DUH” moments. Over 20 years ago I made a > loaded 160M vertical with the loading coil at 33’ (the length of 2” > aluminum pipe I had available at the time) and a whip on top for another > 18’ (total height ~52’). Inductance was chosen to resonant the whole system > at the low end of 160m. Works like a champ. Then I discovered that the > antenna worked great on 40M as well. The “DUH” moment: 33’ is a quarter > wave on 40M. The inductance was sufficient to isolate the lower 33’ > section. Serendipity is a wonderful thing! > Larry K5LJ > > *From:* Rick Hiller via BVARC > *Sent:* Sunday, July 10, 2022 6:17 PM > *To:* BRAZOS VALLEY AMATEUR RADIO CLUB ; TDXS List > *Cc:* Rick Hiller > *Subject:* Re: [BVARC] Seeking Antenna Design Info > > Short answer to my design dilemma or "how to kill a hot Sunday > afternoon" > > Focus is -- Shortened dual band dipoles that use a coil for loading a > lowband wire and using the same coil to "trap" RF into the higher band, > inner portion of the wire. [I was wondering how this worked, as JP had > sent me a EFHW design using a single coil using this trick] > > The dual band antenna consists of a higher band antenna wire (i.e. 40 > meters) with coils at the ends of this portion of the wire. Short end > wires are added on the outside of the coils to get final resonance on the > lower band. The coils play the part of low band loading coils and the > part of "traps" for the higher band RF. Why? > > The coils are positioned at the ends of the center, 1/2 wl, higher band > wire portion, which is a standing wave high voltage point and the XL of the > coil is designed to be quite high to stop any high band RF flowing outside > the high band inner wire...making a resonant dipole for 40 mx. When > using the antenna as the longer 80 meter wire, the coil has less XL (XL = > 2PI F L), and since the coil is within the standing wave sinusoidal curve, > it acts as a loading coil. RF will continue to flow out to the very end > of the antenna wire thus providing resonance at the lower frequency. The > antenna, of course, has the benefit (to some) of being shorter, physically, > due to the loading effect of the coils. > > The coils must have sufficient windings to produce the correct XL for each > band and they must be positioned properly within the wire for this dual > band system to work. > > References: --Alpha Delta' DX-CC and EE antennas use this design with > their ISO-RES coils. > --In Bill Orr''s Antenna Handbook 1979, he gives 2 example antennas -- > 20/80 and 40/80, which I modeled and they work out just great -- nice dual > band wires. Orr also comments that this dual function coil trick was first > referenced in 1926 by the Bureau of Standards, but I could not find any > such publication about it. > --In Pop Com Feb 1988, W9INN built a 160 and 80 sloper vertical using this > trick (thanks to Matt, KM5VI). > So.......y'all probably knew all this, but I am still learning. Thanks > for reading or deleting. I've had fun! Time for dinner..... 73...RH > > > On Sun, Jul 10, 2022 at 11:38 AM Rick Hiller <[email protected]> > wrote: > > I appreciate everyone's comments and direction. I knew if I pondered the > question long enough and with the help of a few antenna craftsmen the > answer has come to me. It's nice to have knowledgeable and interested > friends. > > For others, discovery is a light going off or a bell dinging when you get > the answer you seek. For me, most of the time, it is either a Homer > Simpson "DUH" or a 2 x 4 to the side of the head. It's was no different > this time. The answer to be told soon after a few EZNEC runs. > > Thanks for all of your comments. > > Regards...Rick W5RH > > On Sat, Jul 9, 2022 at 8:57 PM Rick Hiller <[email protected]> wrote: > > Loading coils used also as traps are my focus. Alpha Delta uses what they > call an Iso-Res Isolation (trap) and Resonator (loading coil) in their > antennas. Bill Orr mentions a few antennas in his books that use them, > but they are cookbook examples for building and nothing on the design of > the dual function coil. > > Can any one provide me with a book reference or a URL etc. that might > provide clues as to the design, building and measurement of such devices? > > I realize that certain coils have a self-resonance and I can find info on > that, but there are no references that apply this self-resonance to an > antenna design. > > Contact me direct, if you wish. [email protected] > > > More detail if you wish to read about it..............JP sent me a design > of a shortened EFHW for 80 and 40 that uses a 110 uH coil near the end of > the antenna wire that provides loading for 80 MX and traps 40 MX energy, > thus making the antenna dual band. I modeled it in EZNEC based on the > basic design, and lo and behold the antenna when doing an SWR sweep does > indeed resonant on 80 and 40. Displaying the currents on the wire show > that it is used at full length on 80 and stops at the coil on 40. > I think I am missing something in my research. TNX for reading....any > help appreciated. > > TNX ES 73....W5RH > Rick Hiller > *e-mail: [email protected] choke * > *Cell: 832-474-3713* > *Physical: 9031 Troulon Drive > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g>* > > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g> > * Houston, TX 77036 > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g>* > > > > -- > Rick Hiller > *e-mail: [email protected]* > *Cell: 832-474-3713* > *Physical: 9031 Troulon Drive > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g>* > > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g> > * Houston, TX 77036 > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g>* > > > > -- > Rick Hiller > *e-mail: [email protected]* > *Cell: 832-474-3713* > *Physical: 9031 Troulon Drive > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g>* > > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g> > * Houston, TX 77036 > <https://www.google.com/maps/search/9031+Troulon+Drive+%0D%0A+Houston,+TX+77036?entry=gmail&source=g>* > > ------------------------------ > ________________________________________________ > Brazos Valley Amateur Radio Club > > BVARC mailing list > [email protected] > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > Publicly available archives are available here: > https://www.mail-archive.com/[email protected]/ > > _________________________________________________________________ > To unsubscribe or modify your subscription options, please visit: > https://lists.tdxs.net/mailman/options/tdxs-list/mullani%40tlite.com >
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