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 >> 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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