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[TowerTalk] R-7 HELP

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Subject: [TowerTalk] R-7 HELP
From: (Kimo C. Chun)
Date: Sun, 20 Jul 1997 14:36:53 -1000 (HST)
Dear Fabio:

On Sunday, 20 Jul 1997 you wrote:

>I am looking  for some help about an secon hand R7 antenna.
>Just assembling the antenna to checkout any problems before
>leaving Italy for my Expedition to 5H1 next week i have
> found  that I have a spare tube of  17.8" instead of a 14" tube
>marked AF in the manual. This tube is a tube between the 20 and 17
>traps, but the disatance from these traps is 16" and with a 17.8" tube
>it's sound difficult. I observed also that the 20 m traps  is different
>from the figure. Probable who has selled me the antenna had a
>wrong manual.

  My R-7 is from about 4 years ago. The manual is dated 11/92.
  I found that you need to follow the picture drawing for proper
  orientation of the traps. They frequently mismarked the traps
  on the wrong end with label indicating UP. I have seen this on
  more than one R-7.

  My manual does not list an AF tubing piece but rather two AE
  pieces of 1" x 14". Between the 20 and 30 mtr traps and between
  the 17 and 20 mtr traps. I just went out and verified this by
  measuring it. The manual goes from AE to AG and skips AF.

  I cannot comment on why you have that 17.8" tube. Maybe they
  redesigned the 20 mtr. trap and compensated with the tubing
  length change.

  Upon completion of mine I was fortunate to be able to sweep test
  the antenna with a return loss bridge and found all resonances
  to be pretty much as expected. A friends' new R-7, when swept after
  construction, showed the 20 mtr and below resonances to disappear
  intermittently. It was a bad trap which Cushcraft promptly replaced.

>Any advise?? Is the manual wrong or may be are there two version
>of  the antenna not notified ???

  It would not surprise me that there may be more than one version
  of the antenna. The ones from my production era were poorly designed
  at the fibreglas insulator. Not enough fasteners holding it to the
  tubing. I heard they had made some change some time after I bought
  mine. My plastic balun box cracked from the misalignment stress of
  its mounting brackets.

  Also, due to normal 10 - 25 mph trade winds here in my valley the
  tubing piece AC just below the lower X-hat developed a permanent
  bend in it causing  a tilt from vertical of most of my antenna.
  Again, under-engineering in my opinion.

  Other than that, I used it for a couple of years and was quite
  happy with its performance. I had no other antennas to compare it
  with but it did a job for me. It is most critical to keep all
  other antennas and metal objects as far away from it as possible.

  Good luck, DX


  Kimo Chun, KH7U

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