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DIY 6' parabolic, cloned!

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  • DIY 6' parabolic, cloned!

    I built a clone of the Channel Master 4250, the 6' brother of the 7' model, the 4251. Every knows the CM parabolics were discontinued around 2000 and IF anyone has one which they have refurbished and have put up for sale, it will cost you your life savings or you go to the bank for a loan to buy it. There are some ridiculous prices on fleaBay or CraigsList for refurbished 4251's. And if you decide to go the professional CATV parabolic route, you can go to Wade Electronics and purchase one of their models. You will probably break the bank buying one of theirs also.

    Just for kicks, I wanted to see if I could build a similar design parabolic and what kind of performance I would get. I researched this project diligently for about one month, along the way collecting tons of pictures found on the internet. I then spent one week designing this antenna in professional design software, attempting to match the measurements for the 4250. So now - the antenna has been built. It took me the better part of 4 days to build this antenna. And now I really would like to know how it performs. BUT - I have been waiting for any type of DX to show up here in southwest Missouri, quaintly known as the *Tropo Black Hole of the Midwest." Its hard to tell if the parabolic will have any kind of respectable performance during a really good tropo opening, since I'm still waiting. The antenna has been complete for about 30 days.

    In the pictures below, I have it mounted on a temporary tilt-over mast, anchored to a concrete slab. I've tested it for one week, facing due south (my best DX direction), with the antenna sitting as seen in the pictures. There is about two feet below the parabolic to the ground. During the one week test, (not counting my locals), the antenna was receiving two stations signals almost 24/7 in sub-decode (no decode), during virtually no DXable weather conditions:

    KAFT 9/13 Fayetteville Arkansas @ 106.14 miles;
    KFSM 18/5 Fayetteville Arkansas @ 107.78 miles.

    These two stations would occasionally get strong enough to fully decode, but most of the time the DX conditions were almost non-existent, yet the signals for those two stations were there almost constantly.


    General specs of the parabolic:


    6' radius parabola X 11" depth at center;
    X3 10' pieces of 1/2" rigid PVC to construct perimeter of parabola (third piece cut to finish length to complete 6' radius);
    x2 10' pieces of 1/2" rigid PVC (cut to 6' pieces for vertical support);
    1/2" galvanized hardware screen in center as extra duty reflector;
    Several pieces of antenna aluminum rod, placed horizontally at 8" spacing;
    x2 bay driven antenna array from recycled 4 bay CM UHF antenna, spaced at 32" in front of the rear center of the parabola.

    An observation about the PVC support arm for the antenna array - from the U-bolt clamp on the mast, the support arm bows some due to the weight of the antenna array. I haven't figured out yet what to do to *straighten* the PVC curve, without adding any extra weight on the support arm.

    Pictures:

    Channel Master 4251, the 7' model;
    x3 pictures of my DIY 6' parabolic with 2 bay antenna array.

    I would like to have comments and opinions about taking on a project like this. This is my third antenna design to complete.
    Attached Files
    Jim Thomas
    Springfield, MO EM37

    "Let's just plop them in front of the TV. I was raised in front of the TV and I turned out TV." - Homer Simpson


    Fall & Winter 2019 dx equipment
    Antennas - Antennacraft MXU59 UHF antenna & home-brew version of Antennacraft VHF Y-10-7-13 antenna @ 25'. Both antennas fed through a Channel Master 7777 30dB pre-amp.
    Tuners - Zenith DTT901 converter box; AirSpy HF+ sdr; Silicon Dust HD Homerun Dual ATSC tuner, using Rabbitears autologger support.

  • #2
    That's cool, Jim.

    You might consider using some Fiberglas pieces, in place of PVC, where sagging is an issue.

    Eventually, my P-7 is gonna have to come down to fix all the damage from the March 1st storm. When I do this, I'll put the tape measure to the antenna and get all of it's dimensions for you. I found the paperwork, from when I modified / restored it but, there are so many numbers scribbled down I'm not sure which ones I finally landed on. :-(

    73, Ed NN2E
    Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds
    "You Might Be a Redneck If...
    Your TV is on 24/7.
    Your TV has been permanently on for over a decade.
    The only time your TV is off is during a power outage.
    Your TV gets 512 channels, but you go outside to use the bathroom.
    Your new TV is sitting on top of your old TV.
    Your TV costs more than all of your other furniture.
    Your deer-stand has a TV antenna on it.
    Your cable provider has no idea that you exist."
    Jeff Foxworthy

    Comment


    • #3
      "........southwest Missouri, quaintly known as the *Tropo Black Hole of the Midwest."

      LOL!!!!

      Comment


      • #4
        If your antenna turns out to be successful you could start your own business. There is a market for a parabolic uhf antenna that isn’t a wallet buster. I would pay $250 for a 4250 style antenna.

        Comment


        • #5
          I see someone is using my picture of the parabolic antenna.

          Comment


          • #6
            PCTools, whatever your name is....are you the one last fall that was advertising a refurbished one for sale on Craigslist? That's where I found that picture and a couple more.
            Jim Thomas
            Springfield, MO EM37

            "Let's just plop them in front of the TV. I was raised in front of the TV and I turned out TV." - Homer Simpson


            Fall & Winter 2019 dx equipment
            Antennas - Antennacraft MXU59 UHF antenna & home-brew version of Antennacraft VHF Y-10-7-13 antenna @ 25'. Both antennas fed through a Channel Master 7777 30dB pre-amp.
            Tuners - Zenith DTT901 converter box; AirSpy HF+ sdr; Silicon Dust HD Homerun Dual ATSC tuner, using Rabbitears autologger support.

            Comment


            • #7
              First significant DTV dx with this antenna

              http://forums.wtfda.org/showthread.p...6023#post46023

              It was *marginal* to say the best, because I don't think my area was suppose to be in on this tropo event, which was mostly centered over the Gulf states, more so over Texas. I finally managed to get to the Houston market, at 545 miles.
              Jim Thomas
              Springfield, MO EM37

              "Let's just plop them in front of the TV. I was raised in front of the TV and I turned out TV." - Homer Simpson


              Fall & Winter 2019 dx equipment
              Antennas - Antennacraft MXU59 UHF antenna & home-brew version of Antennacraft VHF Y-10-7-13 antenna @ 25'. Both antennas fed through a Channel Master 7777 30dB pre-amp.
              Tuners - Zenith DTT901 converter box; AirSpy HF+ sdr; Silicon Dust HD Homerun Dual ATSC tuner, using Rabbitears autologger support.

              Comment


              • #8
                Jim, that is outstanding work.
                Danny
                Shreveport, LA
                Mexico/Latin America TV DX ID Tips http://www.tvdxtips.com
                Submit and read DTV Stats http://www.tvdxexpo.com/dtvdxrecords.html
                TV and DTV DX Photographs http://www.tvdxexpo.com
                My Photographs of 100 Mexico TV DX Local IDs http://www.tvdxexpo.com/100mexicotvids.html
                More than 1,100 TV logs since 1994

                Comment

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