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Coax question

Discussion in 'Amateur Radio Antennas' started by Peter Walker, Apr 2, 2011.

  1. Peter Walker

    Peter Walker W9WDX Amateur Radio Club Member

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    What affect do two coax lines running beside each other have on the other or does it really matter?


     

  2. depark

    depark W9WDX Amateur Radio Club Member

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    Dosen't really matter. Both cables are sheilded. I have 2 RG-213 cables running about 40 feet in the same raceway and haven't had any problems.:D
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    They should have no effect whatsoever. They are shielded cables and as such shield themselves from each other. Now having said that, if common mode currents are present on either of the lines due to improper feeding of the antenna such as feeding a balanced antenna directly with coax cable, then any grounded conductor (like the coax shield) can indeed have an effect on things. Probably in about 99.9% of the cases you can run as many cables in a bundle as you want too. Even separate receive only lines will not pick up the transmitted signal from the cables nearly as much as the antennas themselves will pick it up. The key is to ground all coax cables in a bundle. I have run a half dozen coax cables as well as rotor cables and DC control lines in the same bundle without any hint of trouble.
     
  4. Peter Walker

    Peter Walker W9WDX Amateur Radio Club Member

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    Thanks for the replies. Reason I was asking is because I was looking to mount the J-Pole I'm building up on the roof near my other antenna and the coaxes for both would run beside each other at some point. What is the minimum distance I can put two antenna's next to each other? They are both verticals.
     
  5. C2

    C2 Sr. Member

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    I would guess a couple wavelengths...4 being ideal
     
  6. Beetle

    Beetle Sr. Member

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    For what frequencies? Very important.
     
  7. KM3F

    KM3F Active Member

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    The simple answer to the question as posed is it has no effect.
    There are other circumstances where there can be interaction.
    When these other circumstance prevail, there is a problem with common mode current on the outside of one or both of the feedlines that should not be there.
    This can be from mismatch at the antennas' ends of one or both feedlines.
    More than you ask but you get you monies worth from this reply.
    Good luck.
     
  8. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    a FEW questions are understandable,............ don't ya think you are kinda overdoing it?

    Dit Dit
     
  9. W5LZ

    W5LZ Crotchety Old Bastard

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    How close can two antennas be mounted? It sounds like a simple question but it has a few 'catches' that aren't all that simple, so the answer is going to depends on several things (one of them being the frequencies of use). The only 'simple' answer I can think of is that they should be as far apart as is practical. If the two antennas are 'close' in frequency, they should be further apart than if they aren't.
    I think it'd be safe to assume that one of those antennas would be for 2 meters. So, one 'ball-park' figure for distance would be the length of that antenna. That's just a very rough estimate, nothing significant about it otherwise. If both antennas are for the same general band, then further apart is 'better' than not. There's always some interaction between antennas, the idea is to minimize that interaction as much as you can.
    I honestly think that there isn't any 'set' distance for antenna separation. It's whatever you can manage and still 'live' with the results.
    - 'Doc
     
  10. C2

    C2 Sr. Member

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    I was considering worst case scenario where you have two identical antennas, and co-phasing effects. At one wave separation, you will have considerable effects, not so much at two waves separation. I know that four waves separation for identical antennas did not seem to have any appreciable effect. I'd still want to put my 2-meter antenna at least two waves separation from an 11-meter vertical (at least 12 feet), but here you may experience some effect on the 11-meter system. Just avoid multiples like a 1/4 or 1/2 wave from the 11-meter system and you'll probably be better off.
     
  11. Peter Walker

    Peter Walker W9WDX Amateur Radio Club Member

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    The main Antenna is an Antron 99 which I will be using for 10 Meter to 40 Meter and the 2nd Antenna will be the Cactus Super J-Pole I'm in the process of building. It will be 2 Meter and 70cm. Given what everyone has posted and with a bit of further confusion, I think what I may wind up doing is probably mounting the J-Pole on the back deck which will make it lower than the Antron but far enough away to count for 2 lengths I think. I just gotta figure out how I'm going to run the coax for the J-Pole.
     
  12. Peter Walker

    Peter Walker W9WDX Amateur Radio Club Member

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    How do you mean "overdoing it"?
     
  13. ranger56528

    ranger56528 Member

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    I was told it doesn't effect a thing,When my 25ft RG8 coax gets here tomorrow i will be running 2 RG8 coax cables side by side for 20ft,one coax is for my 40m-10m dipole and the other RG8 is 50 ft long and will be hooked up to my 80/40/20/15/10/6/2/70m Vertical witch i still need to tune for 80-6 grrrrrr :headbang.......
     

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