Using 75 ohm RG6 Quad???

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI6BCX, Feb 18, 2011.

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  1. KI6BCX

    KI6BCX Ham Member QRZ Page

    Hello Friends,

    I found out I can stick it to the HOA and hang a multi-band dipole, but it will take a +/- 400 foot coax run to a hillside outside their boundary. I can fairly easily lay a PVC conduit line to the site, but the cost of RG8/U is presently out of my budget.

    I've heard about Emcoms making use of 75 ohm TV coax during Katrina and in Haiti, but was wondering just how it would work for everyday use?

    I was thinking of shorting the cables to provide more conductor to handle my max 100 watts and use 1:1 Baluns at each end to connect to the 50 ohm SO-239 connections at the tuner and antenna.

    So, will this affordable way work at 400'? Will it get me on the air for 20-80 meters until I can afford the RG8/U? Or am I way off the charts on this idea?

    Thanks to all in advance!

    P.S.; And yes, I've talked to the hillside owner and have full permission for the antenna. He also likes the idea of beating the HOA.
  2. VK1OD

    VK1OD Ham Member QRZ Page

    If the line is operated at low VSWR, losses are probably manageable. For example, with a 50 ohm load (so VSWR=1.5), loss is about 50% at 20m, better at lower frequencies.

    You said a multiband dipole. If that means operating the coax at high or worse VSWR, the picture gets worse.

    Paralleling the coax reduces Zo, but matched line loss is the same.

    I would make sure that the coax used uses a solid copper inner conductor for best loss below 10MHz.

    Last edited: Feb 18, 2011
  3. KI6BCX

    KI6BCX Ham Member QRZ Page

    I have the option of buying a 500' roll of twin lead as opposed to the 1000' run of single. Shounds like I should go for it. And I'll check on the inner conductor.

    I was thinking about going with a 10m-80m G5RV. I'm open to alternitive suggestions and comments.


  4. VK1OD

    VK1OD Ham Member QRZ Page

    This is not very clear to me. Twin lead can mean so many things. Is it twin RG6? If so, why is it more suitable than single RG6?

    G5RV with the hybrid open wire / coax feed arrangement operates the coax at very high VSWR on some bands, and I have already suggested that will have high losses. Have you researched the G5RV at all?

    If you are to use RG6 as you proposed, you will achieve higher system efficiency if you operate at low VSWR, so you should consider multiband antennas that have low VSWR on each band (eg fan dipoles, trapped antennas etc).

    You will probably still need an ATU to mop up impedance transformation at the tx end of the line.

  5. VK1OD

    VK1OD Ham Member QRZ Page

    I should have mentioned that under the same conditions, efficiency of RG213 (or RG8) would be around 52%, about 1.5% higher. That might temper your desire to purchase RG213.

  6. K9KJM

    K9KJM Ham Member QRZ Page

    About the best low cost way to run 400 feet would be to locate some surplus cable TV "Trunk line" Or "feeder" hardline coax of at least 1/2", Or better 3/4" diameter. Find a local cable TV construction crew, Offer them a bag of donuts and you should be able to get lots of it. (Called spool ends) While you are at it, Ask for a few common cable TV "Pin" type connectors... Ask for the ones the splicer cut the pins too short on.... They adapt directly to a PL 259 type connector. (Usually you will have much better luck finding a construction crew, Going through the cable TV front office sometimes does not work so well) This "hardline" is smooth sided, 75 ohm, Aluminum, And being filled with foam dielectric, Has close to zero scrap value. Most companies are very happy just to get rid of it. IF you get really lucky you might even find some that is "jacketed" for direct burial. Buy the crew a case of soda or beer besides the donuts if you do!
  7. W0BTU

    W0BTU Ham Member QRZ Page
  8. KI6BCX

    KI6BCX Ham Member QRZ Page

    I would like to address this myth right now... Here in CA, all bringing donuts and sodas to cable construction crews will get you is fat crews!

    OK, such tactics may work in the midwest and eastern states where such crews are friendlier, union and one dosen't need advanced foreign language skills to explain your need. But here in SoCal all you get are funny looks from the foreman and angry looks from the crew who long prior called dibbs on any scrap they can possibly salvage the slightest amount of copper or aluminum from!

    If anyone has scored in this manner, my hats off to them!

  9. KI6BCX

    KI6BCX Ham Member QRZ Page

    Sorry for the confusion... Some call it "shotgun" because it's side by side. The rolls I've seen at the mega store all say "Twin" so that's what I called it.

  10. KM1H

    KM1H Subscriber QRZ Page

    I also use CATV hardline for TX runs up to 450' and out to 750' for Beverages for receive only. Even on 6M a 450' run of 3/4" and larger has very low attenuation to a matced antenna. With a typical 10M G5RV VSWR in the 2:1 range the total loss should be under 2dB 24/7 unlike open wire line or transmitting twin lead. While the loss will be negligible on RX unless you are working at the noise level it could impact your TX being good copy at times. Heck today the MUF is above 30MHz and 10M is wide open to SA and some Pacific islands; signals are pounding in.

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