Static charge on my EFHW?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0EP, May 24, 2019.

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  1. W5LZ

    W5LZ Ham Member QRZ Page

    If SWR changes with power level you got a problem somewhere. SWR is a 'ratio' and it doesn't change because of how much power is being run through the antenna system. If there is a change then there's a change in the "R" in the impedance. A resistance change can be from a very large number of things, heating of a part of that antenna system (including feed lines) is the most common reason, probably. (You may substitute impedance/reactance
    for resistance if you want, its a matter of your understanding.)
    One source of this kind'a thing is the meter. Recalibrate the thing after a 10 - 20 percent power change. That power change percentage depends on the meter, they ain't all made the same. Another source is in any transformer used in matching impedances, they can get hot and really cause problems in accuracy. Which brings up something else that's interesting! Just how much importance do YOU place on a "perfect" SWR?...
  2. KE0EP

    KE0EP XML Subscriber QRZ Page

    It seems logical that any antenna system requiring unwanted energy to be dissipated through grounding is less efficient than one that radiates this energy. I've always come back to balanced antennas after trying other designs--I would imagine this has a lot to do with it.
  3. AA5CT

    AA5CT Ham Member QRZ Page

    Too much reliance on 'magic transformers' wound on lossy cores that also can be magnetically saturated; what's not to like?

    That, and to your point, I run balanced forms of antennas here too, and have less EMI/RFI effects and can easily run legal limit power at will as well.

    Realizing though, not everybody can, or, more importantly, some impose artificial limits on themselves OR are not aware of just what IS possible, even on no-tree and small property.
  4. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Yes. Reading these posts will demonstrate that this is quite common.
  5. K6BRN

    K6BRN XML Subscriber QRZ Page

    The SWR changes only happen when the matching transformer cores overheat and their characteristics change; read up the thread. And in the EFHW-8010-2K, this takes substantial sustained, average power to do. The cores generate some heat when driven hard; more on the lower frequenct bands and when the antenna height is low. That heat is trapped in the plastic box housing them, which makes a decent insulator. On SSB, this is no problem at all. On RTTY at 1 KW, it can be a problem.

    Moral of the story: 1. Get the highest power version of the antenna, 2. "Know the limitations of ALL your gear". For example, My big Mosley Yagi is limited to 600W on RTTY because of its TRAPS. Very common to have power limitations in amplifiers, exciters, antennas, baluns and coax.

    Are traps magic, too? Nothing magic about EFHW antenna technology; it's been around since the Hindenburg. The matching transformer cores are not saturating - they are overheating, unless you believe the initial heating is due to saturation, which I do not.

    It continually amazes me how so many people reject ideas that are new to them without giving them at least a try. Not Invented Here Syndrome? Pretty silly. But that's how people work, sometimes. More complex than antennas. :)

    Brian - K6BRN
  6. AI3V

    AI3V Ham Member QRZ Page

    Is there any issue with your antenna where the solution isnt to buy something else from you?

    AA5CT likes this.
  7. AI3V

    AI3V Ham Member QRZ Page

    Interesting sales tecnique, comparing your antennas overheating problem to the most famous aviation conflagration in history.

    AA5CT likes this.
  8. AH7I

    AH7I Ham Member QRZ Page

    I did not catch the band this is happening on.
    First thing I would do is take it down and visually inspect everything.
    Check: connections; for signs of heat stress; cold solder joint; arcing; cracked compensating cap; ....
    If you don't find a problem by inspection, then consider occult failure.
    Assumption can cost time and money. Whoa, my cars not running right. "You need a new catalytic converter son". Damn, it was just a loose vacuum hose.

    73, -Bob
  9. AA5CT

    AA5CT Ham Member QRZ Page

    re: "It continually amazes me how so many people reject ideas that are new to them without giving them at least a try."

    Look who isn't trying (can't try?) link coupling, a technique lost on the present generation.

    Embrace the power of resonance as employed in a link-coupled matching circuit.

    I think this is a real problem, we have moved away from tried and true technology to 'a weak substitute' that has definite 'hard' limits as we have forgotten our past and ignored the hard realities of physics (like the Curie point in magnetics).

    We've ventured away from what used to be standard practice in RF coupling circuits (link coupling using magnetic fields) in the last 30 yrs relying now instead on what appear to be 'simpler' circuits with wire wrapped around a donut-shaped ferrite core.
    K2XT likes this.
  10. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hmmmm. Not sure what the complaint really is. Different products with different designers take different approaches. No big deal. If you feel you know of a neglected, excellent approach that would yield a better product that appeals to the customer base, it's an open opportunity for you to exploit and perhaps you should go for it. But know the needs of your market before you do. Because (as I've said many times before) the market votes with its wallet, and that is a harsh and fickle vote indeed.

    Brian - K6BRN

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