Joe Thank you.
Yes I agree. I've got PVC insulator arms that I've already bought fittings for them that will allow me to create a three wire cage spaced any distance I'd like. I presume the cage should be similar in width as the Skyneedle. Say 10" to 12" width. Thanks and I'll keep u posted. Carl AG6X Sent from my iPhone > On Feb 14, 2014, at 3:44 PM, "Joe Subich, W4TV" <[email protected]> wrote: > > > > Is the single 14AWG too thin causing goofy readings? > > Absolutely! Treating the Sky Needle and the #12 wire as a folded > dipole and using 8" for the diameter of the tower, you have a 16:1 > step-up with the single #14 wire. > > If you made a cage of 4 or 6 wires with a 6 to 8" diameter, back of > the envelope calculations say the impedance with the 67' tap point > would be much closer to 50 Ohms *and* the bandwidth would be much > wider. Even three parallel wires spaced 12" or so would have a much > greater effective diameter and would reduce the step-up you see by > a great deal. > > Of course, if all you can do is a single #14 wire, use an Omega > match or an L-network to bring the impedance down to 50 Ohms. > > 73, > > ... Joe, W4TV > > >> On 2/14/2014 6:14 PM, Carl Braun wrote: >> List >> >> Some of you may have followed my efforts in trying to shunt feed my >> 90' Tri-Ex Skyneedle with 20 meter yagi at 93'. I'm still unable to >> find any sort of resonance point on the tower. To refresh everyone's >> memory here are the specifics: >> >> 90' Skyneedle that is 12" round at the base and 4" round at the top >> >> 13' of mast out the top >> >> 5 element Telrex 20M monobander mounted at the 93' level. No other >> antennas on the tower >> >> 1 ½" copper pipe as a radial ring that surrounds the concrete base >> that measures 4' x 8' rectangle. Three 8' ground rods are connected >> to the radial ring via 1" copper strap that is .125 thick. >> >> Currently I have 27 14AWG insulated wire radials. Most of the >> radials are 20' to 50' long with three at 90 to 120' long and four of >> them connected to my 40M vertical array which have 100 count radials >> 50' to 100' each. >> >> The tower is grounded to each ground rod via 1" copper strap .125" >> thick and, as mentioned above, the ground rods are connected to the >> radial ring with the same strap with copper clad stainless screws. >> >> When I bolted the gamma arm to the tower at the 90' height I dropped >> a single 14AWG wire to the ground where my FLUKE meter read ZERO ohms >> between the radial ring and the end of the gamma wire with no >> fluctuations so I'm confident that I have good continuity throughout >> the tower. >> >> Here are the readings that I saw on the MFJ analyzer with the gamma >> arm mounted at the (4) points on the tower that are available... >> >> With the gamma arm mounted at 90' and 36" spacing I saw 425 ohms at >> the end of the drop wire on the MFJ >> >> With the gamma arm mounted at 67' and 36" spacing I saw 380 ohms at >> the end of the drop wire on the MFJ >> >> With the gamma arm mounted at 46' and 36" spacing I saw 240 ohms at >> the end of the drop wire on the MFJ >> >> With the gamma arm mounted at 28' and 36" spacing I saw 120 ohms at >> the end of the drop wire on the MFJ >> >> At all of these points I was able to knock down the R with my honkin' >> 1050pf cap to some resonance sort of resonance at 1.825 MHz but, as >> most everyone has indicated, I should be able to find a 50 ohm tap >> somewhere on the tower. I can't find it. >> >> When I had the gamma arm mounted at the 90' level. I was able to put >> my baby variable 160pf inline to bring the 425 ohm impedance down to >> about 60 ohms and the antenna heard very well; especially on the 1700 >> KHz broadcast band, with a 2.4:1 Vswr. Similar results could be seen >> at the other levels too as long as I brought the R down with a >> variable cap. Yesterday, with the gamma arm at the 46' level (and >> 240 ohms on the MFJ) I was able to put the big variable inline to >> bring the reading to 24 ohms with a TRUE X=0. With a 22 ohm to 50 >> ohm UNUN, I saw 1.3:1 Vswr on the output of the UNUN. I worked a W2 >> in NJ and a W4 in Florida with just the 1000D. BUT...again...I'm >> bringing the R down with the capacitor...not finding 50 ohms anywhere >> on the tower. >> >> Is my radial field so poor that I'm seeing these goofy readings? >> >> Is the single 14AWG too thin causing goofy readings? >> >> I'm back to scratching my head. >> >> Comments from the list? >> >> >> >> Carl AG6X >> >> _________________ Topband Reflector Archives - >> http://www.contesting.com/_topband > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
