Date: Wed, 11 Oct 2017 17:10:04 -0700
From: "Richard (Rick) Karlquist" <richard@karlquist.com>
To: Jim Thomson <jim.thom@telus.net>, towertalk@contesting.com
Subject: Re: [TowerTalk] 80 Meter yagi question
On 10/11/2017 10:11 AM, Jim Thomson wrote:
> ## Aluminum only conducts 60% as good as copper. .25 inch OD copper =
> .417 inch OD aluminum.
> Jim VE7RF
>
<That is only true at frequencies below which skin effect is
<significant. For RF frequencies, you need to take the
<square root of 60% which comes out to 77%.
<1/4 inch copper = 5/16 inch aluminum.
<Rick N6RK
## are u sure about that ? K6STI coil software doesnt depict that effect.
Nor does other software.... unless they
are both wrong. I also used Termans equations..and did it by hand. They all
concur. This was calculating ESR.
That was done at 7.1 mhz. I was only interested in 40M at the time...so did
not try higher freqs. I did try 80m,
and got the same results. Al vs CU. In this case, the AL tubing had to be
aprx .642 OD to equal the ESR of
.375 CU tubing. Closest thing to that is .625..which is readily available.
## I also tried removing the cu tubing tank coil in one of my amps..and
replacing it with an AL tubing coil... and both are the
same .25 OD, and aprx the same wall thickness. Uh was identical, as was the
turns, spacing between turns, and also OD
and ID of new AL tank coil. Did not have to touch the tune and load either,
dead on. Aluminum coil ran hot..... go figure.
Those tank coil tests were all done on 15M.
## alumoweld wire..and also copper clad or copper bonded steel is another
issue.... but I have not done any exhaustive tests on those..yet.
I did notice that stuff like RG-303 with its silver plating, which is over
the copper bonding..which is over the steel core..... on software,
appears to flat line about 9.2 mhz and below... power wise. My guess is, the
skin depth is deep enough such that the current is now into the steel core.
RG-400 doesnt have that issue, nor does RG-142. RG-304 also has a steel
core..same issues.
## But what the heck do I know,.. I just experiment. Besides, copper tuning
is cheap at any home depot or supply house. Then I silver plate it
with the cool-amp goop...just so it looks nice. Bare copper drives me nuts, I
lose sleep over it, looks un finished to me.
Later.... Jim VE7RF
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