[Lowfer] Al Loop Conductor?

K2ORS k2ors at verizon.net
Mon Nov 7 20:04:37 EST 2011 

Bill,
      I received the following comment from Rik Strobbe:
"Hi Warren,

aluminium has a higher resistivity (28x10^-9 Ohmmeter) than copper (17x10^-9 
Ohmmeter) but it has a larger skin depth (Al = 260 um, Cu = 210 um at 
100kHz).
That makes an Al wire only 33% worse than a Cu wire of the same diameter.
Regarding mechanical strength it might be a good idea to inforce this by a 
steel wire support.

73, Rik  ON7YD - OR7T"

----- Original Message ----- 
From: "Bill Ashlock" <ashlockw at hotmail.com>
To: <lowfer at mailman.qth.net>
Sent: Monday, November 07, 2011 7:58 PM
Subject: Re: [Lowfer] Al Loop Conductor?


>
> Hi again Scott,
>
> Thank you for the positive comments on my loop experiments. I am looking 
> forward to doing a similar study of loop performance variables at 500K, 
> particularly with loops supported and in full contact with trees.
>
> I got to thinking about your use of #2 ga Aluminum and checked out my Loop 
> Article #2 which has a comparison of various conductors types (185K). I 
> show the Rac of #2 copper to be close to that of RG-8 and was wondering if 
> you or anyone else has had the chance to compare these Racs. I would think 
> that just the difference in Cu vs Al would amount to a 1.7X increase in 
> Rac for the #2 Aluminum...But considering you are running an incredible 50 
> Amps I realize this is a totally different ball game. Maybe it should be 
> called "The Battle of the Loop Conductor Meltdowns" :)
>
> Best regards,
>
> Bill
>
>> Date: Sun, 6 Nov 2011 18:05:49 -0800
>> From: sthed475 at telus.net
>> To: lowfer at mailman.qth.net
>> Subject: Re: [Lowfer] Al Loop Conductor?
>>
>> Greetings Bill
>>
>> I have only built one single conductor (#2AWG AL) loop thus far and it
>> works very well and have no data to offer comment on Rac of CU vs AL...
>> Thanks to your efforts much of my design effort was based on your very
>> good papers on the topic and designing a tuner that could handle in
>> excess of 50A key down.
>>
>> Using indirect means of approximately determining the impedance of my
>> loop revealed a better than expected performance when compared to
>> modeled solid circular conductor.  I'm making an educated guess
>> (hypothesis) that this is related to the greater surface area of the
>> stranded conductor itself.  Perhaps this is something you care to study
>> in greater detail?
>>
>> My qualitative opinion of this being the 'perfect' loop conductor was
>> based on my wallet not being greatly lightened to purchase the conductor
>> and my back not overly strained to carry it away and install.  I believe
>> this is an engineering compromise that I feel favours the sensibilities
>> of most operators (price and weight vs a slight compromise on the
>> performance CU would provide.)  As I have alittle more leeway on 2200m
>> compared to the Lowfer band this compromise MAY amount to something
>> negligible and be overwhelmed by the other advantages.  Maybe not so on
>> Lowfer?
>>
>> During operation, it appeared to perform well enough that for me there
>> was no interest in delving into the nuisances as JA7NI awaited...
>> Particularly since I could achieve my 1W EIRP with ease now.
>>
>> Is my overall hypothesis correct? I'll leave that to the experts such as
>> yourself to explore and explain.
>>
>> 73 Scott
>>
>>
>>
>> On 11/6/2011 5:06 PM, Bill Ashlock wrote:
>> > Hi Scott,
>> >
>> > Considering the exchange of info on this topic I conclude we have the 
>> > density and DC resistivity of Cu vs Al pretty well in hand but what 
>> > about the Rac of Cu vs Al? Has anyone measured the Rac of aluminum 
>> > conductors... and at different frequencies? Also we shouldn't forget 
>> > the 'proximity effect' and the 'skin effect' when using large diameter 
>> > conductors. I proved at 185K that the reduction in Rac was quite small 
>> > when the conductor diameter was increased. Even separate insulated 
>> > conductors twisted together netted little improvement over a single 
>> > conductor and only when the spacing was approximately 1" was there a 
>> > worth-wide improvement. Twisted, insulated, conductors do not define 
>> > Litz cable. The interweaving needed is much more complex than this.
>> >
>> > Bill
>> >
>> >> Date: Fri, 4 Nov 2011 21:07:43 -0700
>> >> From: sthed475 at telus.net
>> >> To: lowfer at mailman.qth.net
>> >> Subject: Re: [Lowfer] Al Loop Conductor?
>> >>
>> >> Hi Warren
>> >>
>> >> My 100m perimeter LF loop is constructed of similar AL wire.  You'll
>> >> find it the PERFECT loop conductor as it's much lighter and cheaper 
>> >> than
>> >> copper.  The conductivity issue is not that big of a deal as my
>> >> conductor had much better conductivity than calculated.  I figure this
>> >> is due to the increased surface area based on the stranded nature of 
>> >> its
>> >> construction.
>> >>
>> >> Another nice feature of neutral supported cable type conductor is the
>> >> insulation is tough and will have been tested by UL/CSA or similar to
>> >> have a dielectric withstand in excess of 3KV.  No arcing here ever.
>> >>
>> >> Just ensure you use a suitable compound on any joints to mitigate 
>> >> oxidation.
>> >>
>> >> 73 Scott
>> >> VE7TIL
>> >>
>> >>
>> >> On 11/4/2011 5:29 PM, K2ORS wrote:
>> >>> Hi,
>> >>>       I am considering using Aluminum service drop wire (3/0 gauge) 
>> >>> as a
>> >>> conductor for an LF transmitting loop. I know that the conductivity 
>> >>> is not
>> >>> as good as copper but it weighs so much less that I can use a larger
>> >>> diameter conductor.
>> >>> Has anyone tried this? How would it hold up when flexed by the wind ? 
>> >>> Other
>> >>> thoughts?
>> >>>
>> >>> 73 K2ORS
>> >>>
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