Hi Gary: I don¹t mind your 25 cents.
What I figured out was a way to actually measure the Zo. I use an Oscope and a signal generator and about 3m of line under test. I terminate the line with a 10-turn pot. I bang a 1MHz square wave into one end and watch the scope while carefully adjusting the pot. When it¹s matched, the square wave is not distorted and the amplitude is at the same ratio as the change in impedance from 50 ohms! The scope is In high-Z mode. The interesting thing is how the values are close to the calculated. The lines in the 9:1 are calculated roughly 200 ohms, but measure 190. Jerry Sevick told us his experimental results, but didn¹t tell us how to make a balun. Yes, he added a tremendous amount of knowledge to the art, but I¹m making up the backend of how one actually builds it. Sadly, the photographs in the publications are such poor quality as to only give an idea of the fabrication of the test jigs he made. Lots of really good analysis, but I¹d love to see his raw data. B Bill Crowell, N4HPG Pearland, TX Text messaging one-handed since 1982 From: BVARC <[email protected]> on behalf of BVARC <[email protected]> Reply-To: BVARC <[email protected]> Date: Wednesday, December 23, 2015 at 9:59 AM To: BVARC <[email protected]> Cc: Gary Sitton <[email protected]> Subject: Re: [BVARC] TTFD Part Deux Bill: I'm sticking my neck out here, but here's an idea for window line transmission lines. Use the weighted average of the dielectric constant (dc) for air and the feed line spacer/insulator. In the case of real ladder line, the dc is very close to that of air or approximately a vacuum. The window line I use has 14 AWG wire and is actually spected at closer to 400 Ohms than the 450 Ohms usually associated with window lines using 18 AWG wire. Line losses go up as the ohmic dielectric losses in the separator material is more dense, e.g. solid twin lead is the worst. Another consideration is velocity factor. True air spaced ladder line is about 0.99 whereas ladder lines are more like 0.95. This is all mainly dependent on the dc as the permeability of most dielectric materials is that of air or a vacuum. Again, pardon my 1.5 cents worth on this Bill. 73, Gary K5AMH On 12/23/2015 08:55, Bill Crowell via BVARC wrote: > > All, > > > > > I¹ve received a number of emails from you and I¹ll send out a reply to the > group. > > > > > This is an on-going experiment that I hope to have wrapped up in a few weeks. > I¹m waiting on some material to arrive from eBay. > > > > > Action items: > > 1. Using the PVC box instead of an aluminum box necessitates using a feed line > choke. The material is coax to wind to make the choke. > 2. Testing with a 500 ohm terminator. I¹m fabricating a test jig that will let > me use jumpers to select the values for further testing. > 3. Some have asked for detailed build instructions instead of paying me > <grin>. Of course. I dislike it when people hide the designs as patented and > proprietary when it comes to ham radio. > 4. Some have asked me to do a presentation at a club meeting or 3. My health > has been slowly improving so that¹s possible after the holidaze. > > > > > Since the article was written, I¹ve developed a way to actually test the > characteristic impedance of the flat transmission lines. If you look at the > formula, it is a function of the diameter of the wires, the spacing and the > dielectric constant of the material fine when you have a solid piece of > material such as a TV twin-lead, less so when you have some other material. > > > > > > > > One very important item was left out of the article and will be in the revised > article. Grounding. There is provision for a ground lead on the balun; > however, I¹ve not installed a ground yet. The antenna, being balanced, does > NOT require a ground for operation. This is especially important on 160-40m. A > vertical needs a lot of ground plane for efficiency. > > > > > Grounding at the balun is important for SAFETY. With a wire up 50¹ in the air, > lightning happens. > > > > > Any volunteer to help me install 2 ground rods? One at the antenna and one for > the main station ground. > > > > > 73! > > > > > Bill > > > > > > > > > > > > Bill Crowell, N4HPG > > Pearland, TX > > Text messaging one-handed since 1982 > > > > > _______________________________________________ > BVARC mailing list > [email protected]http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > _______________________________________________ BVARC mailing list [email protected] http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org
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