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Conduit dipole swr issues

Discussion in 'CB Antennas' started by ron103067, Jan 25, 2009.

  1. ron103067

    ron103067 Active Member

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    I built a Conduit dipole cut the poles to 8 foot 7 1/2 inches and cant get the swr down on channel 23 it 2.5-1 on channel 1 it is 2.2 to 1 on 12 it is 2.5 to 1 am i doing some thing wrong I can't figure it out help


     
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    Last edited: Jan 25, 2009
  2. Marconi

    Marconi Supporting Member

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    I think it is too long for that large of element. Try setting radio down in frequency, below channel 1, and see if you can find where it is resonant. Go as low as you have to in order to find a good SWR and that will be the place to start.

    How did you determine your original length?
     
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  3. ron103067

    ron103067 Active Member

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    I went to the dipole calculator should I measure the whole thing with the dowel included or not since it is an insulator. If I run it at channel 20 and set the length for that with equal amounts of the pipe on each side might that help
     
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  4. Robb

    Robb Yup

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    Isn't each leg of the dipole supposed to be 102-108"?
    Maybe you should make each leg 108" by adding 4 1/2" and work back shorter from there. I would use Ch 20 as the guage - too. Is it horizontal or an inverted 'V'? How high is it off of the ground to where the coax hooks in? Minimal is 9 ft; and optimal is 18 ft - as I recall.
    That is what I would do.
    Just two cents worth...
     
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  5. Beetle

    Beetle Well-Known Member

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    Don't forget to include the lengths of the coax (braid and center conductor) when calculating dipole lengths. Start measuring right where they separate, not just to the connection points.
     
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  6. ron103067

    ron103067 Active Member

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    Ok I think I figured it out my antenna is way to long I never took into consideration the coax. Also the connection is 11 foot off the ground it is vertical and the coax is at a ninety degree to the antenna I have the bottom of the antenna 2 1/2 foot off the ground. I have it mounted to a tree trunk could this cause reflection. the tree is only on the ground side of the antenna. Plus about three feet from a shed. Just looking I lke building my own antennas and want to learn to do it right
     
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  7. Marconi

    Marconi Supporting Member

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    Good point Beetle, and remember Ron is using conduit and it is much larger that these wire diople calculators consider when they use a thin piece of wire as a radiator.

    This antenna may surprise you as to how well it will work on the horizontal side with DX. If you get it set a bit closer and can rotate it---it should serve you well. I made mine using a suitable square piece of poly cutting board found in mother's kitchen. Try to keep the feed ends around 2"-3" apart so the pig-tail coax connection is kept short as Beetle notes. This part is where the antenna starts to radiate and should be a part of the physical measurement for your record. My notes are not clear on measurements, but I think our 1/2" conduit length was around 104 1/4 to 101 5/8" for 27.205 up to about 27.505 mHz, using 2 1/8" spacing at the feed point ends of the tubing.
     
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    Last edited: Jan 26, 2009
  8. ron103067

    ron103067 Active Member

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    Thanks for the info will be doing that as soon as I can. 1 more question the dowel I used is wood is there some thing stronger to use
     
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  9. Robb

    Robb Yup

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    Depends how heavy it is - of course. A solid piece of plastic or hardwood - like maple - would be ideal. You may want to consider what the effects of rain water would do, as far as seepage and drainage are concerned.
    Do you have any pictures you can post - that would help a lot.
    Let's see what you got going there.
    Just a couple of thoughts.
     
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  10. ron103067

    ron103067 Active Member

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    I'll try to get them up tomorrow if i get home early enough
     
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  11. Moleculo

    Moleculo Administrator Staff Member

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    Use fiberglass if you want it stronger and more weather resistant. You can get fiberglass rods in various diameters from here: MAX-GAIN SYSTEMS, INC.
     
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  12. ron103067

    ron103067 Active Member

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    Thank you I will deffinatly be ordering from them
     
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  13. ron103067

    ron103067 Active Member

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    Well the weather here isnt cooperating with me to get a pic just wondering would copper be a better material to make this antenna out of just trying to figure out the best way to make this. I really like making my own antennas and would like to try and make more. I wouldn't even mind trying to take a crack at making a mobile antenna.
     
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  14. Marconi

    Marconi Supporting Member

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    Ron, all vertical antennas are adversly affected by the earth and it can really be significant if the voltage end of the antenna is close to just about anything. Much power to a vertical dipole only 2-3 feet above the earth will show heavy losses as heat in the soil. Horizontal polarization is much better in this regard, but it too likes to work high above the soil. The fact that the top of the dipole is above the tree top is of little importance, the bottom is the issue and it may show as much current flowing as does the top. The height and vertical polarization you mention are not serving you well. Your dipole will work, but you may not compare well with other stations nearby and other vertical antennas manufactured for CB that are mounted well in the clear.

    You need the bottom to be maybe 10'-20' high for minimal results with a vertical dipole and that makes all the other requirements for location more difficult. A center fed dipole needs the feedline to exit the antenna perpendicular to the plane of the antenna for some considerable distance in order to avoid the worst kind of pattern distortions and that is straight up. Of course the tree and the shed are effecting you pattern in the worst way. If you have to work your vertical near the ground at your location, it is even more important that you be in the clear for at least a wavelength or more in all other directions.

    It appears to me that you may be doing you antenna building and comparison work in the worst conditions possible.
     
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  15. ron103067

    ron103067 Active Member

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    I will have to move the antenna. I'm just right now testing the swr and trying to see if I have done a good job. I'm always trying to figure out where I can put this antenna. I've got a lot of trees and stuff around, my hope is that this tree I'm using is just a trunk that is approximatley 10 foot tall and want to attach antenna to the top which is higher than the shed. I'm just worried cause the wood dowel I use is a hardwood but it breaks easily. So I'm trying to get something I can use to connect the two sections that is strong enough to handle the weight
     
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