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Re: [Smartuners] Ballun?

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  • Christopher E. Brown
    ... Change the length by a few feet at a time, likely the feedpoint happens to be at a very low or high point. In general, at the output is a very high stress
    Message 1 of 3 , Feb 28, 2010
      On Mon, 1 Mar 2010, Mike Miranda W4DXL wrote:

      > For those who put with my rambling about my RF problems with the SGC 237 and FT-950 I want to say thanks. The truth is the problem was me. A bad shield on a PL259 of all things.
      >
      > I'm using a loop made of 300 feet of #18 speaker wire treetop high in
      > most places, a little lower around the house. The signals seem to just
      > jump out now. I can't get it to tune on 17 meters but it will tune
      > above 1950 on 160 meters! I have to be careful on the modulation, too
      > loud and the burglar alarm yelps!
      >
      > Talking to a fellow on 160 he claimed I should ground the SGC-237 and
      > put a balun on the antenna side of it. From what I have read the SGC
      > manual says not to do this. Still I am intrigued, has anyone here ever
      > tried it?
      >
      > 73,
      > Mike W4DXL


      Change the length by a few feet at a time, likely the feedpoint happens to
      be at a very low or high point.



      In general, at the output is a very high stress location for a balun.
      High voltages, and mismatch.


      If you are loading an antenna that falls into the reasonable range, no big
      deal, but one of the reasons people use things like the SGCs is the
      ability to match more extreme cases.


      A balun, to be more specific a RF choke or "choke balun" is almost always
      a good thing to have on the *input* of the autocoupler.



      Consider the autocoupler to be part of the antenna, and put the choke
      before it.


      Without a stiff choke (think thousansd of ohms across the used bands) the
      control/power and coax shield can become part of the antenna.

      Is it a big win in every case? No, but it does not hurt. I have several
      237s and a 235, have been playing with them for better than 2 years now.
      In almost every case the choke helped. Reduced conducted noise from the
      house or stopped RF from coming back into the house on the shield, etc...
    • Jerome Sodus
      Hello, The topic of baluns (and ununs) has intrigued me for almost two years now and is the object of continued study on my part. I ve not tried the suggested
      Message 2 of 3 , Mar 1, 2010

        Hello,

        The topic of baluns (and ununs) has intrigued me for almost two years now and is the object of continued study on my part.

        I’ve not tried the suggested idea but, from what I think I’ve learned about baluns, it would depend on the feedpoint-impedance of your antenna and the balun’s impedance.

        If the feedpoint-impedance is too high relative to the balun-impedance, the balun gets fatally damaged.

        For some numbers, say for a 50-ohm choke-balun, I’d be concerned if the feedpoint-impedance would be approaching 200-ohms.

        I’m sure that others may disagree; they may know more than I’ve learned so far.

        73 Jerry KM3K


        From: Smartuners@yahoogroups.com [mailto: Smartuners@yahoogroups.com ] On Behalf Of Mike Miranda W4DXL
        Sent: Sunday, February 28, 2010 11:32 PM
        To: Smartuners@yahoogroups.com
        Subject: [Smartuners] Ballun?

         

         

        For those who put with my rambling about my RF problems with the SGC 237 and FT-950 I want to say thanks. The truth is the problem was me. A bad shield on a PL259 of all things.

        I'm using a loop made of 300 feet of #18 speaker wire treetop high in most places, a little lower around the house. The signals seem to just jump out now. I can't get it to tune on 17 meters but it will tune above 1950 on 160 meters! I have to be careful on the modulation, too loud and the burglar alarm yelps!

        Talking to a fellow on 160 he claimed I should ground the SGC-237 and put a balun on the antenna side of it. From what I have read the SGC manual says not to do this. Still I am intrigued, has anyone here ever tried it?

        73,
        Mike W4DXL

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