Posted by
Matt Zilmer-3 on
Apr 15, 2017; 9:56pm
URL: http://elecraft.85.s1.nabble.com/OT-Feedline-question-tp7629317p7629332.html
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
On 4/15/2017 10:52 AM, Lynn W. Taylor, WB6UUT wrote:
--
"A delay is better than a disaster."
-- unknonwn
Matt Zilmer, W6NIA
[Shiraz]
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