Having trouble with the Flex 6500 antenna tuner/memory system on 40 m band

  • 1
  • Question
  • Updated 2 years ago
  • Answered
Measured SWR on 40 meter end fed dipole (with 9:1 unun at fed end and 1:1 unun at ground level) ranges from 7.5 to 8.3.  Sometimes the tuner does not reach "Success" and just shows Mem but tuned swr is 2-2.5.  When I return to a successfully tuned frequency, sometimes the swr is above 3 (pegged on flex SWR meter) and I have to retune.  My coax is grounded at a grounding rod before passing through a conduit to the basement shack.  Length is about 18 ft from fed end 9:1 unun to 1:1 unun.  1:1 unun is to curb rf on coax shield since it is the counterpoise for the antenna.  Also about 18 ft from the 1:1 unun and ground rod to the radio.  Cannot reduce the last 18 ft any more.  Any thoughts on cause/cure?  System tunes up well on other bands which have lower SWR for this end fed antenna.  Coax switch serves as ground point for station. Thanks for any comments!
Photo of Keith - KE4TH

Keith - KE4TH

  • 18 Posts
  • 1 Reply Like

Posted 2 years ago

  • 1
Photo of Keith - KE4TH

Keith - KE4TH

  • 18 Posts
  • 1 Reply Like
Official Response
Update - I was checking resistances and found a 100+ ohm resistance between the 1:1 unun and the lightning arrestor/ground rod on the coax braid side. This same jumper was 0.2 ohm previously. Found the coax ring was about two turns loose on the bottom of the unun! This loose connection may account for the sudden swings in SWR. All symptoms are better now, so I will open another thread if RF on the PC or tuning issues crop up again. Thanks for the interest and comments. Should have checked all the connectors first thing!