[TowerTalk] OT: Inductor Calculator

[Jim Thomson]

From: jimlux <jimlux at earthlink.net>
To: towertalk at 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 at karlquist.com> wrote:
>>
>>
>> This may be helpful:
>>
>> http://hamwaves.com/antennas/inductance.html
>>
>> Rick N6RK
>>