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Imax 2000

Discussion in 'CB Antennas' started by husk269, Jan 1, 1970.

  1. husk269

    husk269 Guest

    Getting ready to install a beam on 40 foot tower and wanting to put imax above beam. How far would Imax have to be above beam to work properly? Thanks Husk 269<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/pimp.gif ALT=":hat">


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  2. Jay in the Mojave

    Jay in the Mojave Active Member

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    Hello Husk 269:



    You didn't say if the beam was going to be mounted Horz or Vertical, or what type of beam?



    For a Horz mounted yagi beam I don't think it would matter to much. I would try to get the I Max 2000 at least 9 feet above the beam, since it uses the out side of the coax shield as the other half of the antenna. And the I Max 2000 doesn't have a lot of antenna square footage. Might not be too hard to do.



    If its a Yagi Beam mounted verticaly, then again I would want the I Max 2000 at least 9 feet or higher above the Boom. It may just work fine mounted closer to the Boom also. But in this case may effect the beams performance.



    You could install the beam first without the I Max 2000 and measure the beams gain and rejection to known local stations and document it. Then install the I Max 2000 and do the same measurements and see if there any significant changes.



    www.a1antennas.com



    Jay in the Mojave


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  3. Jay in the Mojave

    Jay in the Mojave Active Member

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    Hello Marconi 390:



    Yes i tried to make a I-10K without out ground plane radials, as a customer wanted a few. After seeing the results, the SWR was dependent on the mast length, and tunning was erritic. So after measuring all this I never looked back, the ground plane radials work to well to trade off for the convience of putting up a I-10K in a tall tree. This testing also reveled some neat to know stuff about the matching circuits.



    This reminded me, many years ago trying to install a Sigma 4, 3/4 wavelength antenna. I had it tuned to low SWR but when I raised it to the operating heigth, the SWR went nutzoid into the Red on the SWR meter. And the Gamma Matching hardware had to be modified to get it to work, it had a intermittent connection. That was a real charm to have a intermittent connection in the antenna tuning section after it was raised up and all the guy wires where secured. I got the SWR down to a reasonable level by reducing the mast heigth, to what looked like a 3rd Mulitable length of 9 feet, how wounderful, that wasn't in the instructions. Boy did I want to choke somebody over all that!



    Oh by the way I have several Sigma 4 Antennas in the aluminum scrape barrel, maybe I need to post a picture of this, on the web site. Everytime I walk by the barrel, I smile knowing that some poor soul will NOT have a hair pulling contest with them.



    If you look at the manufactures diagram of the Impedance Matching circuit of these fiberglass sticks, how else would you think the energy doesn't use the outside of the coax as a counterpoise, or the other half of the antenna. The manufacture pamplet says a 1/2 wavelength over a 1/4 wavelength.



    By insulating the mast will not change anything, due to again the coax is the counterpoise. Now if you installed the fiberglass stick

    so that the mast was insulated, from the mast and the coax was placed inside the metal mast as to shield the coax, that might be a good antenna comparison test to do.



    One other thing that I have helped with these none ground plane antennas was to add a Toroid Core 2.4 inches ( Amidon FT240-77 avialable at www.amidoncorp.com/aai_ferritecores.htm ) with about 15 turns of coax around the core, and taped into place. This choked was placed at 102 to 104 inches below the antenna connector, on the coax itself. The coax was RG8X so it could wound around the core without exceding the bend radials spec I think. This showed some increase in antenna performance, per the user. I have not tested this myself. As I am pretty maxed out for time.



    I have been asked to build a 4 element yagi beam antenna that was designed to be mounted Horz, with a I-10K Antenna, using the 4 elememt yagi beam, Boom and Elements as the ground plane radilas. Now thats a grerat idea I think, and maybe some day I'll try that design.



    Jay in the Mojave



    www.a1antennas.com


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    Redbeard U812 likes this.
  4. Peddler 356

    Peddler 356 Guest

    I have and have had for 3 years, an A99 mounted 4ft above a M104c on the flat side...no noticable affect on either antenna.


    The Peddler...

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  5. freecell

    freecell BANNED

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    "Personally I don't think an Imax/A99 will have much if any affect on a horizontal yagi styled beam even if they are mounted right at the boom to mast plate or anywhere 1'-9' higher. One thing placing them at 9' will do is put a lot of lateral stress on the mast, beam, and rotor, below as it is not very likely one can guy the vertical AT."



    you're absolutely right marconi........the base or the feedpoint of the imax should be just above where the boom intersects with the element that composes the center of the boom in a balanced design, (3, 5, 7 elements, etc..) ideally from a balanced construction standpoint



    the worst interaction i have ever seen can be mitigated beforehand by simply tuning both antennas into the lower end of the band slightly to offset the distributed capacitances created between the imax and the boom and elements in the yagi immediately underneath. as a result of the capacitance both antennas are effectively shortened, (the resonant frequency of the antennas increases) and both antennas will tune slightly longer than they normally do when used at more separated distances.



    it is also much more beneficial for the performance of the imax if the counterpoise or the ground plane is placed immediately at the base for best results. for those of you who would rather extend them further up, remember this. aside of the pros and cons from the standpoint of managability, the support mast is usually quite a bit larger and thicker metal diameter than the wire conductors on the inside of these glass sticks. and you're talking about a longer overall run, antenna and all. both of these criteria will increase the values of distributed capacitance i mentioned earlier, making them more difficult to properly tune, especially the beam.




    </p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=freecell>freecell</A> at: 5/24/04 12:51 am
     
  6. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Bump Bump this very short thread with good discussions

    Who was FreeCell?
     
    Redbeard U812 likes this.
  7. bob85

    bob85 Supporting Member

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    which one?
    There was more than one guy ( jack ) posting on that account.
     
  8. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Bob, I remembered the handle, but I don't recall anything about there being more than one guy posting on that account.

    Is that like me posting as Grampa and Marconi sometimes?
     

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