Thanks.... So, these numbers are for BARE copper, right? Using insulated wire changes things a bunch....
For instance 18 GA THHN/THWN has an approx. dc of 2.35, XLPE has a dc of 5 or so.... As the dielectric constant gets larger, things get real.... fast. 18 GA THHN/THWN... (dc = 2.35 approx.) To get the same 464 Ohms, the Center to center distance must increase to 7.52 inches or so... The impedance with the quoted 1, 2, and 3 inch "D": 1" = 305-306 Ohms 2" = 359-360 Ohms 3" = 391-392 Ohms I use 300 Ohm, 18 GA copper twin-lead with foam over wires and some hard plastic over that.... It's close to true 300 Ohm... I'll have to go calculate the min size safe against various power levels... The separation distances get big fast with increase in the conductor diameter, too. 73, PS - there is an argument to be made for NOT using bare wire.... if anything MIGHT touch the feedline... and wet wire.... wet wire changes performance a lot... built with insulated wire, the changes are MUCH smaller with wet wire... ______________________ Clay Autery, KY5G MONTAC Enterprises (318) 518-1389 On 4/15/2017 4:56 PM, Matt Zilmer wrote: > Very true! > > Got back in front of my desktop 'puter and made an Excel worksheet to > calculate the characteristic impedance at various spacings and wire > sizes. The real variable is the ratio of spacing divided by wire > diameter (only the ratio matters). Everything else in the formula is a > constant for our purposes. > > 16 AWG, 1 inchspacing: Zc = 436 ohms > > 16 AWG, 2 inchspacing: Zc= 519 ohms > > 16 AWG, 3 inch spacing: Zc= 567 ohms > > 18 AWG, 1 inch sp: Zc = 464 ohms > > 18 AWG, 2 inch sp: Zc = 547 ohms > > 18 AWG, 3 inch sp: Zc = 595 ohms > > Or for you QRO ops: 3/0 AWG, 9 inch spacing: Zc = 450 ohms. 3/0 > (three-aught) is quite hefty, being 0.4" in diameter. Probably > overkill for the average Joe Ham. > > The commercial ladder line I use is 18 AWG with about 0.9" spacing > (hard to measure), giving 451 ohms. I think there is a lot of this > type in use. > > Anyway, for the wire sizes and spacings we would normally use, the Zc > is nearly the same value, which is all I was saying before. > > The formulas for all this are pretty well documented at > http://hamwaves.com/zc.circular/en/index.html. > > 73, > > matt W6NIA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
