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Thread: 300 ohm TV twin lead ?

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  1. #1
    Join Date
    Aug 2008
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    Mpls. , MN.
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    Default 300 ohm TV twin lead ?

    Got my ticket about the same time they got rid of 300 ohm TV twin lead , heard on the local repeater that the local big-box was selling out all , I stopped by and all they had left were a couple of 50' packages for .99 took them both and figured that I might make some pocket J-poles or ?
    Well a couple of weeks ago I ended up with some commercial [ much heavier than what I ever saw in hardware stores ] spools of this , maybe 500' each .
    I have been looking to see what kind of HF antenna designs there were .
    Haven't found much so , that's the question here , some ideas on building some HF antennas ?
    Thanks
    John

  2. #2

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    Quote Originally Posted by KD0CAC View Post
    Haven't found much so , that's the question here , some ideas on building some HF antennas ?
    Thanks
    John
    You can use 300 ohm TV line instead of 450 ohm ladder line for feeding an antenna. It works fine. I have a portable antenna at my Summer lake cabin that uses 300 ohm Tv feedline and have used it for years. It is ok for 100 watt radios.

    A few years ago I made an inverted L out of 300 ohm tv line. I just shorted the TV line at the far end of the L. I used a Dx Engineering choke to feed it. It worked better than using a single wire. I ran legal limit thru it without issue.

  3. #3
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    A simple dipole.

    Just use the wire as is and strip the 2 wires out of theinsulation to the required length would be the easiest.

    There is a lot of information on lengths for differentstiles and bands, the g5rv and the like.

    I had a 120 foot dipole fed with twin lead to a tuner andliked it. I now use twin lead to feed a loop and it is the best- all round-antenna I have.

    If you want something a bit stronger you can use a centerinsulator and heavier wire for the elements but for most applications what youhave will work fine.

    I aim not sure of the power handling capabilities of 300 ohmTV type and will leave that open to the experts but I am sure up to a couple ofhundred watts it works fine.

    TV twin lead ischeap, low loss, easy to work with and works great!

    Joe

  4. #4

    Default

    One thing you might try is to build a DCTL antenna:

    http://ve3gam.webqth.com/?p=555

    With the amount of twin lead you have on hand, maybe you could go into business selling DCTLs!

  5. #5
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    St. Mary's County Md since 2000
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    Default

    I use twinlead for feeding portable antennas like loops and dipoles, as well as for experimenting.

    Other uses might be Folded Dipoles, and bi-directional Beverage antennas.
    "RF gotta go somewhere!"

  6. #6
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    Default

    Well what I was looking for was to use as antenna , not feed-line [ or possible as both ] but to focus on using for antenna .
    Looking at how a collinear is made [ opened up a 2m base antenna ] taking advantage of the pair of wires & insulation , I've seem something with coax done also .

  7. #7

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    Quote Originally Posted by KD0CAC View Post
    Well what I was looking for was to use as antenna , not feed-line [ or possible as both ] but to focus on using for antenna .
    Looking at how a collinear is made [ opened up a 2m base antenna ] taking advantage of the pair of wires & insulation , I've seem something with coax done also .
    The best way to take advantage of your bargain is to use it as a feed line. Feeding a doublet with a higher z line, like 300 ohm twinlead will (in most cases) result in less loss than a lower impedance transmission line like coax. Or, you could make a full wavelength long wire dipole for 20m, and use a section of the twinlead to match it to 50 ohm coax. It will have gain over halfwave dipole. You could also make a G5RV.

    The only purely twinlead antenna I can think of would be a folded dipole. Cut about 1/2 wavelength, short it on each end, cut one of the wires in the center and feed it right there with any convenient length of twinlead back to the shack, where you will need to match 300 ohms to 50 ohms. Well within range of most tuners. (you'll want to use a current balun between the tuner and the transmission line for that one)

    There are j pole designs on the Internet that use TV twinlead. I tried a few and never thought they worked that great, but some people like them.

    You could also Google Franklin Array for some other ideas on antennas, and uses for your twin lead as a phasing element, or tuning stub. Your vertical antenna would use the twinlead sticking out perpendicular to the antenna to create the phase shift. Probably an electrical 1/4 wave with a s/c at one end in the right spot. But you'll need to do some research on that.
    Last edited by K1DNR; 08-16-2012 at 02:42 AM.
    Charley K1DNR

  8. #8
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    I have made a number of folded dipoles for the various bands over the years. The center feed point of a folded dipole made of 300 ohm twinlead is very close to 300 Ohms. You can then use either link coupling or tune the feeders. (On low power I used to put a #47 dial light in each leg and tune for equal brilliance -hi
    (that was running about 10W.
    Have fun and keep an eye out for some RF Ammeters. 73 BTW yes I know a balun could be used but I LIKE tuned feeders for the very low loss factor.
    Dick

  9. #9
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    Thanks getting some ideas to play with .
    One of these yrs. , I hope antenna modeling [ in my mind ] will be 2nd nature , at least for coming up with things to try , would have helped to get into ham radio back in the 60s when I was handed a Heathkit catalog , instead of about 5 yrs. ago , when learning seems to take more effort .

  10. #10
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    I made several HF band antennas out of twinlead.
    Folded dipoles and feedline made from 300 ohm TV twinlead. This worked out well as a lightweight , easily put up and taken down set of antennas for 20/30/40M for travel when on vacations.
    A roll of heavy string taped to each end worked for hoisting into tree branches.
    Used the bal line input on a MFJ tuner where the sig went thru a 4:1 balun.


    Quote Originally Posted by KD0CAC View Post
    Well what I was looking for was to use as antenna , not feed-line [ or possible as both ] but to focus on using for antenna .
    Looking at how a collinear is made [ opened up a 2m base antenna ] taking advantage of the pair of wires & insulation , I've seem something with coax done also .
    73.....JD, FISTS #3853,cc 455,SKCC # 1395,tribune #12,
    Official US Taxpayer

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