"Great Quality" RG6 coax

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by NM7G, Nov 24, 2020.

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  1. KB1CKT

    KB1CKT Ham Member QRZ Page

    Forgot to mention that, I had heard of that problem. I would think cost would imply thicker copper, but that probably isn't a safe assumption (per usual). I know some of those satellite installs pass power to the dishes so thicker copper would be better, ergo the assumption. Might not be valid (steel does carry current and all).

    Not so easy finding data. I found a datasheet for the Southwire stuff I have, but it gives nadda for loss nor copper thickness. Will have to keep digging around for better coax. [I'm not against 50ohm by any means, just a cheapskate at the moment!] Not sure if just searching for "solid copper" will skip over the CCS stuff or not; quick look does find hits.
     
  2. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Southwire is probably ok in CCS as they are a major supplier. They also have the bare copper version .

    I can never get their spec links to work. I suppose you could contact their customer service and have them send it to you.

    Be cautious and check product numbers if you buy at a big box store. They have a habit of negotiating cheaper unique products for their stores that will have a different number.
     
  3. NM7G

    NM7G Ham Member QRZ Page

    Thank you, Steve. This is the crux of the matter for me.

    There's nothing magic about 50 Ohms! It was selected as a workable compromise impedance. It is by no means the only impedance hams might successfully use. I've used 93 Ohm, 75 Ohm, and 50 Ohm cables with no problems, and used open-wire line when it was the best choice. Check this for useful coax history: https://www.microwaves101.com/encyclopedias/why-fifty-ohms. I wouldn't normally look for coax at a Kroger store either, but I've dissected enough raw cable and installed enough connectors to sink a tugboat. We typically want to know what we're buying. The cable has the appearance of quality construction. Marketing it without quantified technical data doesn't surprise me for sale in a consumer focused store, but "inquiring minds want to know.....".
     
    K0UO likes this.
  4. W9GB

    W9GB Ham Member QRZ Page

    Gary,
    Much of the “Cheap, bargain bin” CATV/satellite TV coax is manufactured in East Asia (especially Philippines). Large satellite TV market in that part of globe (>2 billion population).
    1970s CB craze had same issues, due to copper shortages (high cost), some real JUNK coax was manufactured in that decade. Anyone remember Columbia? mfg. in East Asia?

    Appearance of Quality is increasingly difficult (today, you have to discriminate for little misses).
    Steve, WIK pointed out the other issue: Cladding type/thickness over Steel center conductor.

    * Actually 100% copper? You will never know, Copper expensive, cut costs.
    * Thickness? Another great area to cut costs (consumer/buyer will never check).
    For TV usage, scratch off that cladding ... and it’s like a cable break (attenuation).

    * Impurities in steel or copper based cladding. Easy to do ... and becoming common.
     
    Last edited: Nov 24, 2020
  5. KB1CKT

    KB1CKT Ham Member QRZ Page

    So in my basement I have a length of 100' of... not sure what vendor RG6, but I only need 40'. So I bought a 500' spool to fix the problem... More of the Southwire stuff available at Home Depot.

    So I'm trying to measure return loss with 500' on the spool; looking how to do that with the nanoVNA but first tool is the MFJ-259. Reading Duffy's blog he mentions using an integer number of half wavelengths so as to get around the 50 to 75 ohm mismatch. Easiest way to do that is to spin the VFO until no reactance, unless if I'm mistaken. I crimped an F on one end and left the other end open. At 1.29MHz I measured 27j9 for 1.9:1 and at 2.06MHz I measured 29j9 at 1.8:1. [Note the '259 does not show sign, this was "as good as it gets".]

    But I'm at a loss (no pun intended) at the moment as to how measure or read these results.

    Oh--those 29ohm points, that is where I see the open at the line, but transformed into a short. [Not a short because of loss.] So at 1.29MHz I have an odd integer number of quarter waves, and again at 2.06MHz. So if I spin the knob to 1.67MHz I get 198j70 for an SWR of 4.6:1--that is worst SWR so I'm assuming the worst open. I'm not find where j goes to zero, but watching the display very carefully, I think it might be very sharp through zero. 1.29MHz is a wavelength of 233 meters, and the spool is 152.4m (not measured), so...? 2.06MHz is 115 meters. 1.29MHz must be where it's 3 quarter waves, and 2.06MHz is where it's 1.25 wavelengths--no, math works out to be 1.75 wavelengths and 76% Vf. Which doesn't check with 1.29MHz data. Hrm.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    100% copper wouldn't work well with "F" connectors that rely on the center conductor to be very straight and strong as it mates with the female.

    There was real "RG-6/U" mil-spec cable that did have a solid copper center conductor and all that jazz, but the TV industry never uses that and I don't even know if it's still manufactured.:p

    I don't worry much about cable Zo either, as I can accommodate 50 or 70/75 Ohm cable just fine in most applications. Sometimes I use it as a linear matching transformer, and then its electrical length is critical; since TV cable has V.F. that varies quite a lot depending how much gas they inject into the dielectric and other factors, for "matching" I'll use real (mil-spec origin) RG-11/U which has a pretty consistent 0.66 V.F.

    Years ago (back in the late 80s!) I actually measured the V.F. of a lot of "foam" dielectric cables and they varied quite a bit from about 0.78 to 0.84 so if I need a specific electrical length and don't want to set up to measure that, I just use real RG-11/U.:)
     
  7. KB1CKT

    KB1CKT Ham Member QRZ Page

    Ok, I found this page:
    https://owenduffy.net/calc/MllFromRin.htm
    and then the explanation page
    https://owenduffy.net/blog/?p=310
    which indicates 0.7dB per 100' on 160m for this Southwire stuff.

    At 500' of the stuff I can see why my band noise seems so low...
     
  8. KB1CKT

    KB1CKT Ham Member QRZ Page

    For the heck of it: at 145MHz I measure 62j10 at 1.3:1 SWR. I could only get to about 78 ohms for max R. That indicates either 2dB or 3.4dB per 100' on 2m.
     
  9. AK5B

    AK5B Ham Member QRZ Page

    Yeah, but the Kroger stuff is more edible than all the other brands (or so say the squirrels and gophers).

    For the OP: Amphenol is the way to go with RG-6; it's in the bright orange jacket and has gel floodant for direct bury---what all the cable companies use.

    If you cut it multiples of half-wave lengths for a given band you can repeat the impedance seen at the feedpoint. Remember to account for the velocity factor when computing length, as I recall it is 85% but I could be off a bit.

    Search the "KC8VWM Method" in this forum on how to attach PL-259s without an adapter (if interested).

    73,

    Jeff
     
  10. N3DT

    N3DT Ham Member QRZ Page

    I used to get 200' of RG11 which is even better than RG6 for loss, for about $50. I notice the shipping prices have now gone through the roof. I use the stuff for my single band antennas at 1/2WL's with F connectors (and adapters) and haven't had any issues with it up to 1KW. The trouble with it at 6M and up is the R factor tends to always move towards 75Ω the longer you make it. So even half wavelenghts still end up being 75Ω if they're more than a couple wavelengths at VHF/UHF, but the stuff has loss like 1/2" hardline.
     
    AK5B likes this.

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