Jim,
On Sun, Apr 27, 2014 at 2:00 AM, Jim Brown <jim@audiosystemsgroup.com>wrote:
> On 4/26/2014 8:21 PM, Mike Waters wrote:
>
>> You're right about the loss being all in the copper center conductor, Jim.
>>
>
> AND in the shield. ... It's important to realize that "RG6" and "RG213"
> are no longer specifications for the cable that we buy. ...
>
Yes, and all coax with the same label is not created equal.
And what I meant to say above is that dielectric losses are negligible at 2
MHz.
I forget the details, but before I installed over well over 1000' of
Commscope flooded quad-shield CCS F-6 (for both Beverages and the 160m
inverted-L), I took a close look at its loss at 2 MHz. There was only
slightly more loss --0.3 dB max-- in the CCS coax I have vs. solid center
conductor RG-6.
I haven't seen Owen's charts, but there's a good chance they're out of date
> in that respect.
>
His graph showed almost identical, overlapping loss curves for "RG-6/U" and
"RG-213/U" from 1 MHz to almost 100 MHz. I'm 99% sure that Owen's RG-6 had
a solid copper center conductor, and it was something he obtained there in
Australia. I don't know what the shield material was.
Here's what Owen said:
"The graphs are total loss... so copper loss is in both conductors, but if
you examine the geometry of most coax cables, most of the loss is in the
centre conductor (typically around 70-85%).
"For a start, it is 75 ohms... so you have less current, and the ohmic loss
(I^2) is 50/75... that is a good start.
"Remember that ohmic loss in the centre conductor is proportional to
diameter, not diameter^2 as it is at DC.
"All that said, RG6 with CCS centre conductor is not a good choice for low
loss on 160m... there isn't enough copper thickness for that frequency...
you want 150µm cladding thickness for copper like performance."
No critters have ever gnawed on my F-6 here, but it's taken quite a beating
(horse hooves, tractors, trucks, and falling trees) in a few places; some
right through the outer jacket down to the first foil shield. But nothing
that an overwrap of electrical tape couldn't fix. I'm not sure that
hardline lying on the ground --like much of this coax is-- would have held
up as well here.
73, Mike
www.w0btu.com
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