[Lowfer] Al Loop Conductor?

Scott Tilley sthed475 at telus.net
Mon Nov 7 20:53:54 EST 2011 

Hi Bill/Warren

I accounted for the difference in skin depth for CU and AL when making 
my initial mathematical models to compare to operational results and my 
numbers agree with Rik's.  In fact, I used Rik's article(s) as the 
reference.  This is where my claim that there is for some reason better 
than expected results with my system, which I believe is related to 
greater surface area of the stranded conductor...

If you care to delve further into my loop's characteristics the Q is 
measurable by viewing Grabber 2.  I may have crunched the numbers but 
its not obvious in my notebook on the topic as the a quick look reveals 
a decent Q value as I likely didn't dwell on it then as other priorities 
dominated...

73 Scott




On 11/7/2011 5:04 PM, K2ORS wrote:
> 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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