Cushcraft R7 Vertical Problem

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by VE2CY, Aug 31, 2019.

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  1. VE2CY

    VE2CY Ham Member QRZ Page

    Hello, I got an R7 from a SK's estate, and have verified the measurements and re-erected it.

    It works on most bands, except it has an extremely high SWR on 30 and 40 meters (according to my ICOM).

    Yesterday it poured with rain, and I tried it both during and for a time after the rain had stopped, and the SWR was in a workable range (2.0-3.0!!).

    Today, it is back to very high SWR (in the red, according to my Icom 7300).

    Would this be due to a leaky trap ? Why would the rain "fix" it ? When I assembled it, I could not see anything wrong with the traps.

  2. W9GB

    W9GB Ham Member QRZ Page


    The Cushcraft R-7 is a multi-band HF vertical that covers 10,12,15,17,20,30, and 40 meters.
    IF the antenna works fine on the five shorter-wavelength bands (10 -20m),
    THEN the Traps (L-C) on lower portion of antenna are OKAY.

    Your issue is at the Upper Part of the Antenna, TV4 and TV5 Traps & Capacity X-Hat.
    Inductors (coil on fiberglass) within adhesive heat-shrink; Trombone capacitors;
    OR the top X-Hat .

    The “Rain Water” suggests a Bad Electrical connection (corrosion, loose mast).

    1. Traps improperly installed.
    During a Field Day ten years ago, a group of New Radio Amateurs installed all the R7 traps Upside Down.
    They had a Sharp, Clean paper copy of Cushcraft R7 assembly instructions.
    They could not follow the written instructions.

    2. Compression clamps (there are many on the R7 antenna).
    Loose (not tightened), Corrosion, etc.
    Use Burndy Penetrox A®; Jet-Lube SS-30; or Ideal Noalox® on the Telescoping mast section areas,
    that are compression clamped (prevent corrosion and GALLING)

    BD21723A-E2DF-4974-9BCB-78419BF76899.jpeg F445070E-31E2-4C8D-95D0-E636319337D9.jpeg C220F573-7D55-4AE0-B07A-ACA26A78499F.png
    Last edited: Aug 31, 2019
    K6CLS likes this.
  3. KI7HSB

    KI7HSB Ham Member QRZ Page

    I second W9GB's response. You are most likely having an issue of electrical connections between elements. A connection may be loose, but if there is corrosion on the mating surfaces, tightening the joint is futile. Make sure that all metal to metal contact points are clean, free of corrosion and it's always a good idea to apply the appropriate amount of NOALOX or other suitable anti-oxidizing compound to the connection points. Use only as directed...
  4. VE2CY

    VE2CY Ham Member QRZ Page

    Thank you gentlemen - I will be pulling it down to move to a permanent location, and will check out the top section then ! Cheers & 73

  5. W9GB

    W9GB Ham Member QRZ Page

    Cleaning of Telescoping Aluminum Tube Sections.

    3M Scotch Brite pads are made from nylon/polyester fibers,
    coated with an aluminum oxide abrasive.

    3M Scotch-Brite General Purpose Scouring Pad, 08293, Green.
    3M Scotch-Brite General Purpose Hand Pad, 07447, Maroon.
    Mr. Clean's Magic Erasers are made from expanded melamine foam,
    which is extremely abrasive on a micro level.
    It will tear up your skin as well as your knife blades.
    They appear to be soft and squishy - but don't let that fool you.
    The melamine resin has jagged edge profile, at the micro level.
  6. VE2CY

    VE2CY Ham Member QRZ Page

    W9GB - thank you for the info - I was using a cream "Mothers Mag & Aluminun Polish" and it also, like the products above, does a good job on the exposed metal, which turned out to be quite dirty when I separated the sections. However, this brings me to the question - would not the outer tube also be dirty? I could not get the polish inside, and it would be the same problem for the 3m pads or magic erasers. I put back clean shiny tubes, with "Ox-Guard" anti-oxidant on them, into a potentially equally dirty outer tube. I think I still have the same problem, although there was a small improvement. (and are the anti-oxident compounds capable of conducting RF, or did I just actually "insulate" the antenna sections?).
  7. WA6SW

    WA6SW Ham Member QRZ Page

    KI7HSB likes this.
  8. VE2CY

    VE2CY Ham Member QRZ Page

    Wow, I didn't know that existed! The Home depot stores in Canada don't carry those, but I see one listed on the Canadian Tire website - I will go get it tomorrow, thanks for the suggestion!.
  9. WA6SW

    WA6SW Ham Member QRZ Page

    Greg has posted the older instruction manual. Attached is a new version that you may what to check. The 40 meter trap was changed along with the upper dimensions. It sounds that you may have another issue with the rain but this version may be good to have.
  10. VE2CY

    VE2CY Ham Member QRZ Page

    Yes, thank you. I did find that one online at a place that saves manuals, but it is a much more fuzzy copy and hard to read the measurements - this one you have is clear - super - now I can clean the insides of the tubing, and set it up for correct operation. Thanks again.

    Joe, VE2CY
    WA6SW likes this.

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