uses for 75 ohm coax in Amateur Radio

Discussion in 'General Technical Questions and Answers' started by KJ4GXU, Sep 5, 2009.

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  1. KJ4ODU

    KJ4ODU Ham Member QRZ Page

    most TV/RG-6 cable and othe r75ohm is like from 50MHz to 3Gigs, that what we used in installing satellites.
  2. KD0CAC

    KD0CAC Ham Member QRZ Page

    I do not know from experience but from reading , that latter line is better for HF , lower frequencies , and that coax is for higher .
    Then when using latter line with HF , it is now part of the antenna , and should be factored in when designing .
    Just like the length of the antenna wire , the latter line should have certain lengths to use , and lengths to avoid , for specific frequencies .
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    The primary use for ladder line (not "latter" line) is to allow multiple bands to be operated from a single antenna. By using some sort of "antenna tuner" the transmitter can be made to be "happy" with the impedance presented to it by the "antenna tuner". Therefore, the antenna can be operated on several bands.

    Coaxial cable is generally used with resonant antennas and when used with such antennas the attenuation is considerably less than when coaxial cable is used with non-resonant antennas (thus, the use of ladder line for many multi-band antennas). Coaxial cable is considerably easier to "work with" than ladder line, twinlead, "open wire" line, etc. in the fact that it can come in contact with other items, can be buried, and so forth.

    You will find that very few of the top contest stations and other serious operators use ladder line. There are probably a few, but, for the most part, coaxial cable is pretty much the "standard" for such operations.

    Glen, K9STH
  4. N2RJ

    N2RJ Ham Member QRZ Page

    I don't think your fiber provider brings fiber all the way to your TV.

    In most FiOS installs I've seen, the fiber terminates at the ONT in the basement or the side of the house and the rest is Cat5 or Coax.
  5. W2VW

    W2VW XML Subscriber QRZ Page

  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    There are relatively few installations that are "fiber to the desktop", even in high end commercial applications.

    Here in Richardson, Texas, AT&T has "fiber to the brick", which means that there is fiber to the side of the house, building, etc. There is a conversion unit on the outside of the house which converts the signal to Category 5 cable for the Internet and television. The same unit converts the telephone to POTS ("plain old telephone service) 2-wire copper. The Internet/television comes from the conversion unit by Category 5 to a modem (in my house it sits right next to the main computer). The modem then converts the television signal to coaxial cable for distribution to the various television sets. The modem also contains a wireless router that can provide Internet connections to other computers in the house.

    Fortunately, for me, the wireless router had problems with my then Windows 98 computer out in the radio shack. Therefore, AT&T ran a Category 5 cable out to that computer. I don't like the idea of a wireless connection when I am running close to the legal power. Several months ago I purchased a new computer and took the old one out to the shack. It is running XP. However, since I have the hardwire connection I definitely am not going to change anything!

    Glen, K9STH
  7. AG3Y

    AG3Y Guest

    Jim, for NTSC broadcast setups, 75 ohm cable was used to send the video signals from camera to switcher, etc. The reason for this was that all the video amplifiers, and processors, etc. were designed with 75 ohm unbalanced inputs and outputs. Much more 75 ohm coax was used for the transfer of video signals in a studio situation, than were used for the transmission of RF !

    In a Television Transmitter site, most coax is of such a dimension that you would not even recognize the stuff as being RF "cable". I am talking about cast tubing at least a couple of inches in diameter, up to nearly a foot in diameter ! In fact, the center conductor of broadcast coax would make a pretty substantial water pipe !

    Look at this page, for an example !

    73, Jim
  8. KD0CAC

    KD0CAC Ham Member QRZ Page

    I will not take the blame , I blame my computer for bad spelling , also that post was before my 1st cup of coffee !
    That's just one of the things I like about this hobby , is there can be many reasons why , how something is done .
    Thanks for more info .

  9. K9KXW

    K9KXW Ham Member QRZ Page


    Jim: you are completely right, I would have NEVER thought that BC Stations would use COAX to that extreme. That stuff that they use looks almost like sewer lines under city streets or something.

    Thanks for the info AND the website, that's neat stuff. I think I'm understanding now SO AGAIN THANKS.

    73 Jim
  10. K9RPR

    K9RPR Ham Member QRZ Page

    RG6 as a feedline for 2m/70cm

    I have a large amount of RG6 Quad leftover after installing satellite tv in a new house. Can I use it for a feedline to my antenna for 2m/70cm, and is there any thing I need to install to make it match well with my 50ohm rig?
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