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RG-8/U Mini Foam 16AWG Stranded - Power?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K4AVL, Jul 30, 2010.

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  1. K4AVL

    K4AVL Ham Member QRZ Page

    I found some conflicting info on this, and am just looking for an opinion on whether this cable will work.
    I have a reel of probably close to 300' of RG-8/U coax... the wire itself is labeled Tandy Wire & Cable E111378A Type RG-8/U MINI FOAM 16 AWG "CL2" 75C "(UL)"
    It's wound on an original metal Belden "Made in USA - Chicago" blue & white reel, looks like no one would have gone to the trouble to re-wind it onto that from another reel, so I'm thinking (that my guess of its age is from the 70's) that at that time perhaps Tandy actually had it manufactured by Belden.
    It actually seems to be the RG-8X type (about 1/4" diameter), with copper shield and 7-strand 16 gauge bare copper core.
    I've used lengths of it before with great results for Field Day on 20 meters running 100 watts.
    My question is: can I use a full 100' length of it into a 20 meter vertical using power (up to a KW SSB on peaks from an Ameritron AL-80B).
    I read on eham that one gentleman said he ran full legal limit in FL using RG-8X with no ill effect. I would just be using it for mainly SSB, not RTTY at that power by any means. I see though that some specs limit the power to around 700 watts. On CW, the AL-80B is only rated at around 800 watts. The line voltage here where I live in PA now is only 117, not 125 as I had before, so I wouldn't be pushing the power by any means.
    Is anyone familiar with this cable type and if it is actually an 8X cable?
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Yes, it's actually RG8X cable.

    I doubt Belden made it, though, or it would carry their brand on the cable itself.

    I re-spool cables all the time, using a motor-driven cable spooling machine in my garage (which I've had for 20 years, and it was old then!). Re-spooling 1000' of RG8X onto a spool takes maybe 2 minutes, maybe a bit less and the machine wind lays it in perfect layers.

    Distributors often do this, and just grab whatever spool they have laying around.

    As for its robustness, with a matched load (VSWR = 1.0) RG8X can handle a kilowatt easily. The only "issue" is if the load is very mismatched. Under some mismatch conditions the voltage across the cable (center to outer conductor) can be very high and break down the dielectric. I've had this happen, but it takes a mismatch or a fault to do it.

    If your antenna is well matched on the frequencies where you use it, you shouldn't have a problem.
  3. K9XR

    K9XR Ham Member QRZ Page

    I'm not sure about that exact coax, but it sure sounds like 8X to me. I think it should handle the power as long as the SWR is within reason.

  4. G3TXQ

    G3TXQ Ham Member QRZ Page

    I'm not familiar with RG8X but I see that the Times Microwave site quotes 520W average power handling capability at 14MHz. You should divide that by the worst case VSWR; then you can factor it back up according to the transmission mode peak/mean value.

    Steve G3TXQ
  5. K4AVL

    K4AVL Ham Member QRZ Page

    Thanks, I'm actually putting up the antenna as we speak, taking a 10 min break right now. Since it's going to stay up all winter, will silicone the joints and the SO-239 connector. It's going on the garage roof, we have a 4-car garage with a flat roof, 20' x 40'. Hopefully if I am able to run the coax to the house & drill a hole through the wall, I may be on the air tonight (finally) from the new QTH.
    From another thread, it's a 20 meter vertical made from 1/2" steel electrical conduit. Used it with great luck for 2 field days in NC, but now since we moved to PA will make it my main antenna for now (also put up a 2 meter J-pole a few weeks ago). We've just hit the 30 day mark at our new home and the going is slow. Made a new QSL card today.
    View attachment 42053
    Quick question: if the dielectric is breached (arcs) a few times, will the coax degrade quickly or over time? I'm carefully putting it up also to avoid any kinks while installing to compromise the foam.
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    If it's a 20m vertical, is it about 16' tall (1/4-wavelength), or how tall is it?

    If you arc through the dielectric just once, you have made a carbon path that will continuously break down from that point forward. So the answer to the last question is: Yes, and it won't just degrade over time, it will be immediately degraded.

    But if you have a 1/4-wave 20m vertical and radials, and use it only on 20m, your "match" should be great and I doubt this will happen.
  7. K4AVL

    K4AVL Ham Member QRZ Page

    Yes, thanks, it's the exact correct size. So should be ok if I tune to 1:1 before applying power. It's up now, just have to cut the cable, route the run along the eaves and across to the garage roof, then solder on the PL-259's at each end.
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What kind (and how many) radials are you using?
  9. K4AVL

    K4AVL Ham Member QRZ Page

    Four elevated radials, 5% longer than the radiating element with the ends about a foot or so above the roof level, and the main element's base is on a pedestal 5' above that, and the radials connect to it (within an inch or so) at that point using separate electrical ground blocks connected to the SO-239.
    Here's a view of the connection when I first built the antenna about 3 years ago.
    Of course now it's getting weatherproofed. Always worked like a charm in the past, and it should help being on top of the 14' or so tall garage.
    I'm going to be real curious to see what countries I pull in here in N.E. PA as compared to the mountains of NC. There I was at 2800' elevation and favored S. America & Southern/Eastern Europe. Even Ducie Island was a snap on 3 bands I had antennas for. Here I'm at about 650' and have ridges on each side of the valley. Actually, too, I'm on one of the higher spots on a hill in the city.
  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Should work fine. On HF, elevation above sea level is pretty meaningless since the propagation's all ionospheric, anyway.

    The only thing that matters is a reasonably clear horizon, preferably not a "positive" horizon, but either a fairly flat or negative one. That can be achieved at the beach at 0 feet ASL, or in a Kansas cornfield. Being "in the mountains" is usually a bad thing, unless you're on top of one, in which case you have the same advantage as being at the beach or being in that Kansas cornfield.

    Just don't try to use the 20m vertical on a different band! THAT will cause problems with the coax.
  11. K4AVL

    K4AVL Ham Member QRZ Page

    Got it finished this morning, good reception but did not try for any contacts.
    Being that the roof of the garage is 11' above ground, the feedpoint (bottom feed on the main vertical elecment) would be about 16' up, and the top at about 32 1/2'.
    Will try to make a few contacts very shortly.
    I did notice that I can tune it to a 1:1 SWR on 40, 15 and 10 as well and get 100 watts out on my 756 Pro III using my Drake MN-2000 matcher. (only 2:1 on 17 and just 50 watts). I can't find the website where I saw it graphically at one point, but how much loss using coax can I expect on 100 watts on these other bands? I've gotten a bit rusty on how to figure this out, so if anyone has the time, please let me know. Couldn't find it on the Cebik site. It seems it won't be 5/8 wave or any other favorable length for any of these other bands, if I'm not mistaken.
    Of course I will only try using power on 20. I did finally find my box with the 100' length of the heavy Columbia 01109 RG 8/U foam (3/8" dia. approx - legal limit), so I could wire it with that at some point soon.
    Someone on another thread posted that I could easily make a base-mounted loading coil to switch in manually and get it to work fine on 40 meters without loss. I finally found this site:
    and from what I gather from playing with the figures, if my main element is about 16.5', I would need to make a 10 microhenry inductor and that should do the trick. Does this seem correct?
    Anyway, will see if I can make a few QSO's now.
    Thanks to all who have replied.
    Last edited: Jul 31, 2010
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