On Jul 18, 2007, at 8:36 AM, KC4HW wrote:
> Take a look at this link: http://www.epanorama.net/documents/
> wiring/coaxcable.html it
> contains information regarding coaxial cable. The chart displays
> sort of screwy, but pay
> particular attention to the capacitance/ft values of the different
> coax. Notice that RG213 has
> a 30.8pf/ft value. This would be approximately 71.5 feet to equal
> 2200pf.
One thing to consider is that any length of coax doesn't just act as
a capacitor, it also acts as a transmission line, and that will have
an effect on the resulting capacitance.
W8JI wrote about this on his page on coaxial traps:
http://www.w8ji.com/traps.htm
"Coaxial capacitors are really open stubs, and should be treated that
way once they are more than a few degrees long."
71.5 feet of coax is about 96 degrees on 1.850 MHz, so this probably
isn't a good way to get 2200 pF.
> For the inductor, I would try to find a wrecked Butternut veritical
> and use those coils.
>
> However, here is an article that I found on physical construction
> of inductors that I thought
> was very interesting... http://www.arrl.org/tis/info/pdf/9708033.pdf
If you look on the internet, you can find a number of useful web
pages that have electronic calculators.
For example, if you can measure the antenna impedance, you can figure
out an L-network to match it: http://www.daycounter.com/Calculators/L-
Matching-Network-Calculator.phtml
If you want to design an air-wound coil, here's an inductance
calculator:
http://www.technick.net/public/code/cp_dpage.php?
aiocp_dp=util_inductance_calculator
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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