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Need Antenna Help

Discussion in 'Amateur Radio Antennas' started by De_Wildfire, Sep 5, 2009.

  1. De_Wildfire

    De_Wildfire Member

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    I have two antennas up 25 feet, one is a G5RV on the right side of the house which is tuned to 14.6 mhz and an inverted L which is on the left side of the house which is tuned to 3.2 mhz. I use a tuner. I tried running two antennas at the same time but I am not sure if one is just canceling the other one out. When I tied the two antennas together using a T connector, the swr is flat down on 3.9 mhz and I don't need a tuner. Signals are stronger on 75 and 40 meters and I talked to a few VK stations. The problem that I am having is if I test each antenna individually, I have to re-tune it which takes a little time and propagation could change and that can mess up my signal checks on the other end. I've also noticed that stations are weaker closer but at the same time stations are stronger from long distances just by tuning the receive.

    Other information- The G5RV is coax fed and when it gets to the outside of the house, it changes over to 450 ladder line which runs to the center connector.
    It is up 25 in an inverted V configuration. The center point is on the chimney going down to two 20 foot poles in the back yard.

    The inverted L is on the other side of the house and runs from the peak of the house to the ground. The other leg goes to a 20 foot stake in the yard. I have five ground radials burried in the yard which ranges from 75 feet and it goes down to 25 feet.



    My question is, is this thing actually working or is one antenna canceling the other one out? Am I wasting my time? I did notice though that the VK stations are readable now compared to before when they were barely readable. Maybe I am only receiving more since I am putting more wire out there and my transmit is only as good as one of my antennas if they were separate? Anyone have some antenna model program to help me have a better understanding?
     

  2. RickC.

    RickC. Hopeless antenna junkie

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    Now that's interesting. Feeding two non-resonant antennas (or at least they sound non-resonant, the low VSWR point does not always indicate resonance), likely out of phase, each with both vertical and horizontal components.

    A couple of questions-

    Have you had the chance to hook an analyzer or noise bridge to each antenna individually, and then when you have them hooked together?

    What are the lengths of the feedlines to each antenna?

    As an old buddy of mine would say, "Ahm mo hafta thank bout that there".
     
  3. De_Wildfire

    De_Wildfire Member

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    I haven't had a chance to hook up the analyzer or noise bridge yet. On the G5RV, I have about 35 feet of coax which switches over to 450 ohm ladder line.
    On the inverted L, I have about 15 feet of coax to the ground point outside where all the ground radials and and the radiator meet. One thing I did notice though, I must have popped open my garage door even when the transmitter was locked out. I am guessing the radiation pattern changed and I was getting into the wire between the button and the wall and the unit on the ceiling. I know I closed the door. I put everything back to the way it was and now using the switch box on the two antennas. Even though I made stronger contact with a few VK stations last night, something is not right.
     
  4. W5LZ

    W5LZ Crotchety Old Bastard

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    It sounds like the two antennas are 'cooperating' to make a directional antenna. As you've found out, that can be both good and bad. Any time you feed two or more antennas in some 'phase' or another, you will change the overall radiation pattern. Exactly how the radiation pattern changes is predictable, but only by measurements of some type, or by computer program.
    If you do the information collection and plot figuring, I'll certainly run it through 'EZNEC' for you, but I can't do that collecting for you (besides, I'm too lazy). those two antennas are not exactly the most common to be used in that manner, but I don't see why they couldn't be.
    - 'Doc


    Wanna make the thing 'better'? Raise the whole mess another 40 feet! :)
     
  5. N5IT

    N5IT W9WDX Amateur Radio Club Member

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    I would operate these antennas separately using a good coaxial switch and a second tuner if you can afford one. That would likely provide a more predictable radiation pattern for the chosen band of operation. It would certainly solve your testing problem...

    73, Dave
     
  6. freecell

    freecell BANNED

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    antennas are ac circuits. when they are in close proximity to one another they have the ability to couple energy back and forth between them and will continue to do so until they are separated by at least one wavelength from each other at the lowest operating frequency of either of the two antennas.

    also be aware that if the antennas are in close proximity to the house ac wiring that this constitutes additional unwanted coupling and only serves to further complicate the problem.
     
  7. 6 Meters Rules

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    Antenna's Are Certainly NOT AC Circuts !:LOL:They are fed with DC Shure tell you didn't pay attention in class if its True !!!!!! Hook up an Antenna & If it works Great its Called Experimenting , Of Course What Would an Engineer Know They only read it out of a Book & Thats only if they Didn't have MOMMY & DADDY BUY THERE DEGREE FOR THEM!!!!:LOL::laugh::blink::LOL::rolleyes::rolleyes::rolleyes:
     
  8. frankenstein 320

    frankenstein 320 frankenstein 320

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    any new info

    I have read that fore a yagie the best proforments ocours when the driven element is .15 away from the reflector and the directors should be about .20 wavelength away from driver.This was out of a old book. I wanted to know if this sounds right to you or what do you think. I have yagie programs but everyone of them are diferent values or distents from one onother.THANKS.
     

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