[NCARC] Ideas on HF vertical problem

[James Cizek]

  Hi all,

  I have been racking my brain on this one for 2 weeks now and am giving in to
  ask for assistance here.

  I have a very old Cushcraft R7 multiband vertical that I normally use on HF.  The other
  day, something happened and now several bands won't tune.  I had one issue that I knew
  about for sure, the 20 meter trap capacitor cover sun rotted and fell off, the trombone
  style capacitor got water in it.  I carefully disassembled it, cleaned it, dried it, and 
  reassembled / re-heat shrinked it.  Other than that, there is no visible damage to any 
  other components.  

  The matching network is dry, everything is tight, and shows no signs of arcing.  I have 
  measured DC resistance to verify that all connections are mechnically tight. I disassembled
  the entire antenna this weekend and cleaned ALL the tubing with steel wool to clean up
  any dirt/oxidation.

  The first and foremost problem is that it will not tune on 10 meters,  since this band
  is the highest frequency band of the antenna, I am not even worrying about the rest until
  I can get 10 meters working (though, some of the bands will tune, even though none of them
  seem to be natviely resonant anymore) 
  It's supposed to have a 2 MHZ bandwidth on 10 meters with under 1.5 : 1 SWR.   
  Right now, I see 18:1 in the middle of the band.  The MFJ 269B is showing
  a very narrow (5 khz) wide window where the antenna is measuring 50 ohms, but still has a 
  very high SWR.
  I do see a 1.7:1 spot in the band, but it's currently very narrow and sitting at 26 mhz.
  Since 1" of tubing change = 50~100 khz freq change, that would be between 20 and 30 inches
  I'd have to shorten the antenna.  Something else is fundamentally wrong (plus, I can't 
  shorten it that much without removing large sections of tubing)

  I took the 10 meter trap off of the antenna and tried to couple to it using a grid dip
  meter, but found that my grid dipper is now longer working, so no luck there. 

  The couterpoise is clean, and electrically sound, both between the 2 radial systems
  and the matching network.  I also put a 50 ohm terminator on the coax outside and 
  measured it inside (to make sure it wasn't the coax!) It's flat as a pancake reading
  1:1 and 50 ohms on all bands. (The antenna measurements at the antenna seem to match
  the ones taken in the shack also...)

  So, I am hoping that someone will be able to offer any suggestions on what to try
  next, or what to look for.  This has been very frustrating!   I have followed the
  great advide offered here: http://www.qsl.net/ei7ba/r7_vertical.htm 
  to no avail.  Anyone got any ideas?

  Thanks for your time. -James   KI0KN