HFU HF Underground
Technical Topics => Equipment => Topic started by: NJQA on November 03, 2019, 1438 UTC
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Owen Duffy points out that Copper Clad Steel (CCS) or Copper Clad Aluminum (CCA) RG6, RG11, and CAT6 cable are becoming more prevalent. I’ve also noticed that the only 450 ohm ladder line I can find anywhere is CCS.
Owen says that there are no specs on the thickness of the copper layer, and there are increased losses on these cables at lower frequencies compared to pure copper conductors. He notes that losses of .03 dB/m at 1 MHz have been seen. If you have a 100 meter run, this could be significant.
Is this really a problem? The numbers seem to indicate it is something to pay attention to.
https://owenduffy.net/blog/?p=15974
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Thanks for posting this, definitely something to keep in mind.
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I think I lost an hour of sleep over that last night... 8)
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Attenuation due to the copper over steel may be an issue, but I am not sure that I have seen a difference in my long feeds to NDB antennas.
What is possibly a bigger issue is this: these cables tend to have a higher DC resistance per kM than pure copper constructions. If you try to power an active antenna which draws appreciable current - say 60 to 100 mA - over the cable, the DC voltage drop may be an issue.
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An issue often found with the clad stuff is the copper flakes or cracks and a diode junction forms, and you get the results in your rx, or emit a spurious cloud if used to tx. Try not to handle it too much or pull it too tight. The steel stuffs likely not going to stretch much but the loominium surely will.
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Could not find a spec concerning depth of copper plating on RG6. However, for power conductors,
according to one source, the plating can be from 6 to 10% of the conductor diameter (depending on the
conductivity... usually around 30 to 40% of pure copper).
So, at say 6%, (without going through all the math) the depth of plating on a typical 18 awg RG6 CCS center conductor
would be sufficient to allow all the current at 10 mcs. to flow on the copper. However, by the time you get down
to the AM broadcast band, only about half of the current would be flowing on the copper.
The above is based on an assumption of plating and some quick calculations, but you get the idea.
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The stuff works pretty good at 2.4ghz. That's why they make RP-SMA to F adapters.
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An update from Owen, this time looking at ladder line. Maybe not as bad as previously thought, but still something to be aware of.
https://owenduffy.net/blog/?p=16920
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More from Duffy. One ham bought RG6 that started to see performance drop offs below 85 MHz.
https://owenduffy.net/blog/?p=17599
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Thanks, interesting and I'd not considered skin depth in rg6 on hf, will have to reevaluate the coax runs now.
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All RG6 probably not created equal. My hunch is that the name brand made in USA coax sold only through electrical wholesalers may be higher quality than the offshore produced stuff sold at the dollar store. This is only a guess because the problem is trying to find specs for the thickness of the copper clad.
Anyway, my 40/10 meter dipole is fed with RG6 while my 80-10 meter vertical is fed with RG213. Some days the vertical seems to perform better than the dipole while other days the dipole has the advantage. My VHF ground plane is fed with RG58 while my discone is fed with RG6 but no apparent performance difference between the two. My 100' wire antenna fed with RG6 has received many DX NDBs. The RG6 in use on all antennas is supposedly quality material obtained at the electrical supply house. Admittedly none of this is very scientific but just some actual observations.
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I agree with Pinto...not all RG6 is of equal quality. You have to separate out problems caused by poor quality off-shore RG6 from those caused by the use of CCS at the lower frequencies.
In addition, for those sending DC power up the coax, you have to consider whether the additional resistance of steel has an impact on the DC power available at the distant end. That would be easy enough to measure.
What I would like to see is a measurement of matched load line loss of a 1000 ft of CCS RG6 vs 1000 ft of pure copper RG6, of equal quality construction, at 100 kHz, 1 MHz, 10 MHz, and 30 MHz. That would tell me whether this is a real problem or not.
Also, it is becoming harder to find solid copper too. I can’t find ladder line cable anymore that isn’t CCS.
I set up a 1000 foot loop-on-the-ground antenna this Fall, using CAT5 UTP. The cable I bought was Copper Clad Aluminum (CCA). The DC resistance on each conductor was twice what copper wire would have been. I have no idea if this impacted the antenna. I heard plenty of DX on it. Maybe I would have heard more on a pure copper antenna... maybe not.