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 >>> Houston, TX 77036 >> >> >> >> -- >> Rick Hiller >> e-mail: [email protected] >> Cell: 832-474-3713 >> Physical: 9031 Troulon Drive >> Houston, TX 77036 > > > > -- > Rick Hiller > e-mail: [email protected] > Cell: 832-474-3713 > Physical: 9031 Troulon Drive > Houston, TX 77036 > ________________________________________________ > 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]/
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