Cushcraft R7- help required

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by VE6XMX, May 14, 2020.

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  1. VE6XMX

    VE6XMX Ham Member QRZ Page

    Hi friends!
    The bottom most radiator tube found slightly bent from the bottom end (held in fiberglass-f/g-base) in an old R7 vertical antenna. The hole in the tube used to secure the tube with f/g base was only 1" from the end of the tube. I have cut the bent part and now ready to drill the hole. My question is do I have to drill the hole at 1"? I am tempted to insert the tube more into f/g base so that it forms a stronger joint. If I insert more, I see that it stops at the pre-installed rivet protruding inside the f/g base. When inserted more, it will go down inside the f/g base beyond the ground plane clamps mounted on the f/g base.; would this be ok?

    Appreciate if someone can advise what I should do. Many thanks en 73, Praveen VE6XMX,
  2. AA5MT

    AA5MT Ham Member QRZ Page

    If you go too far, you could see a capacitor forming, where the tubes overlap. It will probably drop the voltage rating too.

  3. W9GB

    W9GB Ham Member QRZ Page

    KF6A likes this.
  4. VE6XMX

    VE6XMX Ham Member QRZ Page

    Thanks Tom and Greg. Just for test, I inserted the bottom radiator far down inside the f/g base to rest on the rivet inside and checked was not good. Lowest SWR for 10m was observed at the low end of the band making me think that 10 tube section is longer than 123". I measured it and it is only 121". I think the capacitance formed due to more insertion caused this de-tuning, as Tom pointed out. I will avoid the temptation to make a more secure joint with the f/g base.

    Greg, PA0FRI notes are great, thanks for pointing me to his page. There seems to be more wealth of information which I may explore later. Pass on my gratitude to him.

    I will post an update on how it finally concludes with my R7.
    73, Praveen
  5. VA3QY

    VA3QY Ham Member QRZ Page

    Hi Praveen, send me a message as well. I am also doing a complete refurbishment of R7 as well. we can connect.
  6. VU2XMX

    VU2XMX Ham Member QRZ Page

    sent you an email, Sajid.
  7. W9GB

    W9GB Ham Member QRZ Page

    Vincent, F4CVQ (France) produced a document to outline the production differences of the Cushcraft R7 antenna. Trap measurements & tubing sections shown.
    There are at least two versions (1991, 1994), and three different manuals (dates). The R5 and R7 was discontinued ~1995/1996. The R4 was discontinued, shortly after 17 meters (WARC-79) was opened in North America (1989).

    F5DQK Rebuilding the Cushcraft R7 (Bad Condition) R7 reparation_eng.pdf
    Last edited: May 19, 2020
    KD0CAC likes this.
  8. VE6XMX

    VE6XMX Ham Member QRZ Page

    Thanks Greg for the additional info. I tried but no satisfactory outcome. Fed up a bit :( I think I am not going to put this on roof. In stead planning a delta loop. VA3QY has some great ideas. Thinking of using the same spiderbeam f/g mast to support mutiband vertical. I currently use this installed at ground level and works quite well.

    I very much appreciate your help and form other on this topic.
    Many thanks and 73,
  9. W9GB

    W9GB Ham Member QRZ Page

    Used Antenna Repairs are Easier (and you save $$) — When you have “Basic Shop Skills” and
    DIY Ability to Build most of the commercial antennas on the market.
    These Skills are Best Learned — HANDS ON Instruction (Reading & Videos fall short).

    The Cushcraft R4, R5, R7, and AP-8(A) ARE Repairable — BUT LABOR (Time) Required.
    The web sites provided show you the effort it MAY take for Full Restoration.

    The problems with Used Antennas (Tri-band beam’s with traps, various verticals) are:
    Outdoor Weathering (Age, UV, hot/cold cycling) and Owner/Operator Abuse (Can not read instructions, poor storage conditions, taking frustration out on antenna)
    KD0CAC likes this.
  10. KD0CAC

    KD0CAC Ham Member QRZ Page

    Do not forget materials , I did a few R5 & R7's .
    And a lot of that was to thanks W9GB's links ;)
    After a few of each , I did one for one of the multiple clubs I have belonged to , the club shack , back when we had one , the Mining club - leaving out what political what-ever stuff , the club shack R7 , they went to one of the other , no name company locations to get ahold of double layer , adhesive lined - heat-shrink .
    At retail value was about $75 for one antenna , this was for all capacitors & inductors , so multiple sizes .
    Again that is just the heat-shrink , and no other parts , supplies and labor .
    Added info with these links from W9GB , adding to my stash of info for repair ;)
    Thanks again .

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