From: jimlux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] OT: Inductor Calculator
< And how to get something silver plated once out of high school
<chemistry class I don't know?
< Silver plating doesn't affect the RF resistance very much unless the
<silver is VERY thick - particularly at 2 MHz.
<Copper skin depth at 2 MHz is 1.82 mils (46.1 microns)
<Silver skin depth at 2 Mhz is 1.77 mils (44.9 micron)
<Resistivity is 1.59 for silver, 1.68 for copper
<QQ-S-365, ASTM B700 silver plating thickness is .05 mil, 13 microns
<Complicating this is there's usually a nickel flash/strike plate under
<the silver, to prevent silver/copper migration, and nickel is magnetic
<and lossy.
<But for low frequencies, you're probably better off just making your
<conductor 6% bigger in diameter and that will provide lower overall AC
<resistance.
## personally, I hate the look of bare copper, drives me nuts...so I silver
plate all my cu strap, coils, etc, etc.... with the ..cool amp goop from the
cool amp company in Ore. I also use it on brass machine screws like
10-32, and .25-20, and also phosphor bronze etc. Also used it on contactors
and relays, fuse holders etc, and dc resistance drops like a rock.
## 44.9 microns = 0.001767717 inches. Im sure I can pile on at least
.001 inch..or more of silver plating..esp with multiple applications.
## what about freqs higher than 2 mhz ?? A .25 inch OD tubing coil
will handle
41 % more current, due to skin effect, on 7 mhz... vs the same .25 inch OD
tubing coil
on 14 mhz. The same .25 inch OD tubing coil on 1.8 mhz will handle a
whopping 2.82
X more current... vs the same .25 inch OD tubing coil on 14.350 mhz.....again
due to
skin effect. It goes to the sq rt of the ratio of the freqs.
## re Aluminum vs copper. You require 58-60 % more cross sectional
surface area
if Aluminum is used vs copper. Again, taking skin effect into account,
the tubing used
could be paper thin...like aprx .00176 inches thick..on 2 mhz. The only
way to increase the
puny cross sectional surface area of the tubing is to increase its
circumference by 58-60 %.
And since circumference is directly proportional to diameter, the diameter has
to be
increased by 58-60 %. IE instead of say using .25 cu tubing, you would
have to use .4
Al tubing. Closet thing to that would be .375 al tubing. If instead of
using say .375 cu tubing,
you would have to use .6 inch Al tubing. Closest thing to that would be
.625 Al tubing.
You can also do similar calcs for solid copper wire vs solid AL wire.
Same deal, the AL wire
has to have its diameter increased by 58-60%.
## I have run loads of tests to verify the above over the last 10 years, and
also again recently.
But you also dont want to lose it all by using lousy connections to the given
coil...or using puny gauge
wire to make taps on a tubing coil. I use cu strap for connections to
tubing coils..or other RF
connections and terminations. Strap is unique in that it conducts RF current
on both sides of the strap.
Tubing only conducts RF on the outside. .375 wide cu strap is aprx the eq
of .25 tubing.
## On my seco systems.. Tornado drive, I had them use .25 inch OD plastic
coated Cu...instead
of their .25 inch plastic coated Al. Seco used 12 gauge flex weave wire
to terminate the extreme
ends of their tornado drive coils. This is done since each coil can range
from turns squashed
together.. to coils stretched out, with huge gaps between turns. On a side
note the max to min
uh range is always 2:1 . Each coil on my 80D unit goes from 6.25
uh....up to 12.5 uh. He can make
the coils any size you want, but you still end up with 2:1 max to min ratio.
I did not like the idea of using
a single 12 gauge pvc coated, fine stranded wire to terminate the extreme
outer ends of the .25 cu tubing coils,
so had them modify a standard unit, and use 2 x 12 gauge flex weaves on each
side of the tubing ends. IE:
4 x flex weaves instead of just 1. The idea here is, if 1 x 12 gauge
flex weave handles XXX current on 75m, then
4 of em in parallel should handle 4 times the current. Problem solved.
Jim VE7RF
>
> Just a thought or two.
>
> Terry
> KI7M
>> On February 27, 2019 at 7:26 AM "Richard (Rick) Karlquist"
>> <richard@karlquist.com> wrote:
>>
>>
>> This may be helpful:
>>
>> http://hamwaves.com/antennas/inductance.html
>>
>> Rick N6RK
>>
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