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3816Re: Tranmitting Loop for 6m & 10m

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  • Len Warner
    Aug 1 2:16 PM
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      At 1:21 pm ((PDT)) Tue Jul 31, 2007, in Digest 882, W2XJ wrote:

      >I agree that the loop is too large. The circumference needs to be less
      >than 1/4 wave.

      Only if it is to be a "small" receiving loop: it is marginal as
      a "small" transmitting loop; and there is no restriction on
      (approx) multiple half-wavelengths being used in a large loop.

      For example, see "The Loop Skywire" and the following
      "7-MHz Loop" in ARRL Antenna Book chapter 5, both of
      which have multiple modes above their fundamental (and
      the Skywire as a top-hat loaded vertical too).

      >With 47 cm diameter, you are right at 1/4 wave length
      >before you consider velocity and loading.

      Both MLOOP31 and RJELOOP1 say it should tune 50MHz
      and work with good efficiency with a 25mm conductor...

      >If you go to a diameter
      >slightly less than 40 CM, it should tune on 6 M and be about 60 %
      >efficient on 10 M if you use around 1 inch (25mm) tubing. Also, your
      >capacitor is to large. You need about 26 pf for 10 m and half that on 6.

      ... with about 8pF or 9pF respectively, though we know
      this value must be marginal for Dexter's variable capacitor.

      (RJELOOP1 says only 4.4pF with a 1mm conductor.)

      For 10MHz, RJELOOP1 predicts 29.3pF.

      > With a capacitor 10 times too large, tuning at the bottom of the range
      >could be difficult. What kind of match are you using - gamma match or
      >loop coupling? How much power do you plan to use?

      There are many specific details Dexter hasn't given us,
      (though I see there are some later in this Digest)
      probably because he doesn't understand them himself yet
      or have enough information to reach a decision.

      I suggest it is time for Dexter to do his own legwork and at least
      play with RJELOOP1 (or MLOOP31) until he gets a feel for the
      numbers and preferably also read chapter 5 of ARRL Antenna Book
      to get a handle on the theory and some specific designs.

      And would contributors please _not_ quote most of the history
      of this thread into their messages - especially top-posted into
      reverse or higgledy-piggledy order. I can't easily follow much
      of the quote in your message and I see I wrote most of it!

      Quotes should give _context_ - and they need to be come before
      the reply to do that - not _history_ - we have an Archive for that.


      Regards, LenW
      --
      If you are sending a reply to a message... be sure you summarize the
      original at the top of the message, or include just enough text of
      the original to give a context. This will make sure readers under-
      stand when they start to read your response.... Giving context helps
      everyone. But do not include the entire original! (rfc1855)
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