Using RG-6 / U as a feedline?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KK4NSF, Jul 26, 2021.

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  1. K8DO

    K8DO Ham Member QRZ Page

    I use 81% as the VF for my generic RG-6. When using the VNA to locate a fault even at 300 feet down the line I find the damage within a couple of feet of the VNA called out distance. (working farm and steel blades pulled behind a 20,000 pound tractor don't even notice RG-6 when someone forgets to pick up the tool at the edge of the field)
    Now, there are lots of opinions on this topic. Some seem more based on hearsay as opposed to simple testing. As far as fancy testing methods I have always found that a drum of coax on my bench and the use of an oscilloscope to measure voltage at both ends with a 5 watt, or so, input signal gives me good enough results for the real world. The NanoVNA has made that type of quick check much faster and easier.
     
    Last edited: Jul 27, 2021
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  2. SWL37632

    SWL37632 QRZ Member

    Thanks Glenn this backfills a lot.
     
  3. SWL37632

    SWL37632 QRZ Member

    Agree.

    I do not enjoy 'hearsay' either.

    Based on my testing a dozen years ago, explained in my post earlier this morning (post # 45), this CCS matter seems to not be that significant.....of course the caveat is my test 'experiment' measurement error, and I wasn't looking for copper vs CCS differences....and also, I might have lucked out in getting some heavy thickness copper cladding on my CCS RG6.

    As for Duffy's test method, I understand now what his methodology is.

    However, it seems to me that performing a S21 VNA sweep would have been easier to perform and easier to compare...at least with my VNA you can, as well as do a delta (difference) calculated resultant graphic. Not being familiar with Duffy's instrument, perhaps he had equipment limitations.

    Now, if someone could conjure up a few hundred feet of non-clad steel inner core coax.....
     
  4. K7JOE

    K7JOE Subscriber QRZ Page

    the coax that i always find / buy at the surplus place in 1000 foot rolls is either belden or commscope. I'm sure there is some unbranded coax out there made with chinesium that is probably cladded with less thickness but I am certain the stuff from belden and commscope works great on HF.... even on 160M... based on a decade of using it ! I would like to see what any testing shows... put 100W in...what do you get out the other end... then compare the same to the 50 ohm expensive stuff... no hearsay ..just actual results.

    Good discussion all, as usual !
     
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  5. KM1H

    KM1H Ham Member QRZ Page


    Ditto, mostly surplus from system rebuilds or storm scrapped CATV 75 Ohm hardline up to 1" in diameter, CATV foam version of RG-11 around rotators and pigtails on various wires. RG-6 feeds the various 500-750' Beverages to antenna switches and then 1/2" CATV hardline for ~500' runs back to the house.

    Been that way since the early 80's at two locations and covers 1.8 MHz up to 1296 MHz
     
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  6. W9IQ

    W9IQ Ham Member QRZ Page

    In ham radio, it seems that everything "works".

    Keep in mind that the RG6 style cables are geared for use primarily in the cable TV industry these days. They don't use frequencies much below 30 MHz so don't view the copper coating thickness, as it relates to ham radio use, to be a quality problem. It is simply designed to be fit for intended use.

    But as you say, it would be nice to have some real measurements. I have a fully equipped, commercial RF engineering lab but unfortunately I don't have any of the cable in question. If someone would like to send me several feet, I would be happy to perform the loss measurements using a commercial VNA and compare this to a nanoVNA sweep. Otherwise, I will pick some up at the next swapfest and report the results if someone doesn't beat me to it.

    I am anxious to try out and contrast our latest equipment addition - a Rigol RSA3015N.

    - Glenn W9IQ
     
    Last edited: Jul 28, 2021
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  7. KP4SX

    KP4SX Premium Subscriber QRZ Page

    They use down to 5 MHz and the modern cable is specced for that. The loss is already so low at such frequencies, or even 1 MHz, any difference in the loss curve really isn't relevant.
     
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  8. KM1H

    KM1H Ham Member QRZ Page

    The only measured and reported loss by several is due to thin copper coating is at 160 and below where typical ham lengths are too small to become a problem. Many contractors using RG-6 buy reels from HD or other box stores which is Commscope or an other quality company, they cant afford to use junk.

    Carl
     
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  9. SWL37632

    SWL37632 QRZ Member

    As I recall, in my prior (post # 45) power testing using CCS 75 ohm coax, I juiced the cable up with the maximum power that the IC-735 could put out which is minimum 100 W...more likely about 110W to 120 W, at 160m.

    No 'loss of power' pop-outs recalled.
     
  10. SWL37632

    SWL37632 QRZ Member

    If you can find some junque RG6 and do the tests that would be Great !

    I'd sure like to know, either confirm or dispel this CCS cladding claim.
     

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