[TowerTalk] solid THHN vs jacketed copperweld

[Steve Maki]

Thank you. Very interesting. I never ran across on the google what the 
ideal antenna true R should be for the commercial 4 square black boxes. 
Everything seems to assume that one is using a 1/4 wave vertical with 
*some sort of* good ground system.

My modeling skill hadn't progressed enough to confidently figure all 
that out.

I was measuring through a calibrated test line. I was fairly amazed at 
how long the antenna wanted to be a 70 ohm antenna until I got close to 
the 90° *apex* angle at the center insulator.

It kind of jumps to 50 ohms all of a sudden.

-Steve K8LX


On 9/19/2022 6:41 PM, Gary NA6O via TowerTalk wrote:
> Actually 50 ohms (resistance, at resonance) at the feedpoint is perfect. The 1/4-wave, 75-ohm phasing line transforms that to 100 ohms. Then pairs of elements are paralleled to yield 50 ohms. Finally, a 90-degree hybrid combiner drives the two pairs in proper phase.
> 
> Difference between the two *insulated* wires should be very small. That assumes the copperweld has at least thick enough copper that it doesn’t start looking like a resistor…
> 
> -Gary NA6O
> 
>> On Sep 19, 2022, at 2:57 PM, towertalk-request at contesting.com wrote:
>>
>> From: Steve Maki <lists at oakcom.org <mailto:lists at oakcom.org>>
>> Subject: [TowerTalk] solid THHN vs jacketed copperweld
>>
>>
>> Wondering whether there is any substantial difference between #12 solid
>> THHN and #12 PVC jacketed copperweld (steel) in terms of cutting a
>> dipole to length.
>>
>> I'm in the process of installing a K8UR style 80M four square. I trimmed
>> the first element to length using THHN. Then I decided that I should use
>> steel wire for at least the top half of the elements because of the high
>> wire tension I ended up with after pulling the feed-point out far enough
>> from the array center. It's an issue with not enough acreage around the
>> tower.
>>
>> Even so I ended up with a 50 ohm antenna rather than the desired 30-40
>> ohm antenna per the DXE instruction manual. But that's an entirely
>> difference issue (though I'd appreciate any comments on that as well).
>>
>> Should I expect the steel wire lengths to be pretty close to the THHN
>> lengths, or should I re-do the initial step of carefully cutting the
>> first element in isolation?
>>
>> TIA!
>>
>> -Steve K8LX
> 
> 
> 
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