Cushcraft X-7 SWR Problems...

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB1ZQ, Oct 15, 2017.

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  1. W9GB

    W9GB Ham Member QRZ Page

    Hal -
    The issue with furniture caps and readily available “look-alikes” —
    Ultra-Violet light (sunlight) eventually destroys them (cracks, breakage).
    I switched to DX Engineering tubing caps — no failures yet.
    I noted the MFJ switched to adhesive heat shrink tubing
    with 2:1 or 3:1 shrinkage for Cushcraft trap “cap” replacement (R-7000).


    BTW, I stopped using black UV-ties ... and switched to using either:
    stainless-steel worm clamps or 3M friction tape (just like Andrew, dB, and Motorola used in 1950s).
    The Mobile “Cell-Site” installers switched to stainless during last 4G/LTE upgrade/build-outs.
    They noted that about 1/2 of plastic UV ties from 3G installs had failed
     
  2. KB1ZQ

    KB1ZQ XML Subscriber QRZ Page

    GB,

    The caps were what failed here... well aware of the tie wrap problem. I use 3M Rubber tape (130C) and seems to last forever...

    Know all about the Cell side of the business, been a Cell Tech with (SWB, Cingular, AT&T for the last 23 years - USAF 20 yrs - 10 as an installer prior to Cell work)... Antenna is up and all I need to do is cut to length the coaxes and put connectors on them...

    Hal, KB1ZQ
     
  3. W9GB

    W9GB Ham Member QRZ Page

    It actually does.
    The original 1957 install on my father’s tower still had the rubber and friction tape,
    when we took it down in 2002. The Andrew coaxial cable swept clean, as well.
     
  4. VE7NZ

    VE7NZ XML Subscriber QRZ Page

    I am hoping Danny or an X7 user can help with this. I installed a new X7 this summer and was really happy with it. Great design both mechanically and electrically.

    SWR was as expected on 10/15/20 and could be tuned with my icom internal tuner on 6/12/17. However, after a week, I noticed that the SWR was now high on 20m. It was closer to 2.5:1 instead of the normal 1.5 or less. The resonant point had moved up frequency. Without explanation, it would return to normal after a while but would also go high SWR on me once in a while too. I then started having the same problem on 15m. Sometimes 15 is acting up, sometimes 20, sometimes both. 10m has never had a problem.

    Here are some factors:

    1. Transmitting while rotating the antenna does not change the condition - meaning it is not appearing as if it is a loose joint somewhere.
    2. Rain and temperature seem to make no difference. I even used the garden hose to soak the antenna as a severe test and it made no difference.
    3. Before I installed it, I tested all traps for DC continuity and found two with issues. I took them apart, tightened the loose screws and then they tested fine.
    4. Of particular note - on 20m, if my SWR is 1.5:1 or better and I start increasing power from 100W to 1kW, at some point the SWR jumps to 2.5:1.

    It's not easy to take the antenna down but I will do what I need to in order to fix this. However, I welcome suggestions as to where to start looking. Could it be the traps on the director or does the test in #4 suggest it is more likely a driven element issue?

    Thx. Adrian. VE7NZ
     
  5. VE7NZ

    VE7NZ XML Subscriber QRZ Page

    I don't see a way to edit or delete my original msg. I found a questionable SO-239 in the output of my amplifier. I may have resolved this! Testing will continue. Sorry for the distraction. If it reoccurs, I will provide an update.

     
    WA4SIX likes this.

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