Cushcraft X-7 SWR Problems...

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

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  1. KB1ZQ

    KB1ZQ XML Subscriber QRZ Page

    Hi, I have an older Cushcraft X-7 / X-740 antenna I am having problems with. This antenna is a 10-15-20M beam with a 40M dipole added as an extra element. Over the years the antenna has proved its value as a great performer for me and it withstands the Oklahoma weather great.

    My problem is that I have developed an SWR problem on 20M and cannot seem to narrow it down. When dry all is great. When it rains I get a very bad level of SWR and it gets progressively worse as the wetter it gets. Example: yesterday I was flat across the band, it rained last night and now I am at 3:1 and should it rain further it will drop to unusable... this problem ONLY presents itself on 20M; 10 and 15 are NOT affected. The antenna only has one feed point for all three bands. 40M is fed separately.

    This antenna is large and heavy, in my current location a crane will be needed to lower the antenna for any maintenance. So any thing I can come up with prior to going that route would be helpful.

    Any assistance would be helpful.

    Thanks

    Hal, KB1ZQ
    OKC, OK
     
    IK2WSO likes this.
  2. KM1H

    KM1H Ham Member QRZ Page

    Id suspect the driven element such as a loose clamp. Since the Element 7 is right at the mast it is an easy removal.

    If it is the tip of Element 7 that antenna is still small enough to tip the boom so it can also be removed without a crane.

    Carl
     
  3. E73M

    E73M Ham Member QRZ Page

    You will need to get it down and check the traps for bugs nest accumulation. That is a common problem with traps made with tube covers.
    [​IMG]
     
  4. KB1ZQ

    KB1ZQ XML Subscriber QRZ Page

    Carl, KM1H - when you refer to Element 7, you are referring to the Driven Element for 20M... I ask as the X-7 has 4 Driven elements all tied together with a phasing network fed with a Balun....

    Dan, E73M - the only traps in this antenna are the ones (10M & 15M) on the un-powered Director on the very front element of the antenna...




    upload_2017-10-15_17-48-13.png
     
  5. E73M

    E73M Ham Member QRZ Page

    :) Yes, I know where the traps are, but any change in traps will affect 20m SWR.

    Of course, it could be something else like the bad connection on tip EN tubes on the longest driven element but if 15M looks good when it is wet and SWR raise on 20m, likely the log-cell is OK.

    From my experience, the director makes most impact on feed point impedance and likely could be some connection problem at the transition from coil to tip tube on Trap T6 because in that case the 15 and 10m will not be affected.

    In any case, you will likely need to take it down for a checkup...

    BTW I designed the X7 and spend a lot of time perfecting it on the range by adjusting the traps and director resonant frequency to get the best compromise between overall SWR and Gain/FB values across the three bands.

    At that time my callsign was T93M, hence I named the traps T9 and T6 :)

    73 Danny E73M
     
  6. KB1ZQ

    KB1ZQ XML Subscriber QRZ Page

    Danny, thank you for the information... I love the antenna, I live in Oklahoma and it handles the weather here in a fantastic manner. From the Winter ice storms to the Winds it takes it without a hitch... I had a HyGain Th11Dx prior to this and lost it in the May 3, 1999 tornado - went from a good antenna to $17 worth of scrap aluminum in minutes...

    I put the the X-7 / X740 up to replace that antenna and it has performed super since. This is the only problem I have had with it, and to be honest, it has been in the air since August 1999. My big problem is I live in a residential area and have no place to put the antenna when I take it down without dismantling it to work on it... So maybe it is time to take it down and go thru it to see if I can get another 20 yrs out of it...

    I do have one other question for you, looking at the antenna measurements for the antenna, there is one set of dimensions for the antenna dated 8/98 and the recent manual shows a different set of measurements... can you explain this... or does it really matter... looks like they lowered the freqs by expanding the elements...

    Thanks for a fantastic antenna...

    Hal, KB1ZQ
     
  7. E73M

    E73M Ham Member QRZ Page

    Thanks, Hal,

    Regarding the manuals, the last time I have assembled X7 with 8/98 manual was in 2004 at E71EZC, you can see me in picture inspecting it before CQWW WPX contest.
    Two more X7s are assembled by my friends in Bosnia and all work fine.
    I left Cushcraft in August 2000 and do not know what happened after that especially when amateur antenna division was sold to MFJ by Liard Corp.

    I have performed "customer service" for X7, X9, and MA5Bs very often for the past 17 years when people decide to seek help from me after they do not get support from the manufacturer.

    BTW if you take down the antenna, change the BALUN to real 4:1 Current-type wound on two separate cores.

    Best 73 Danny

    [​IMG]
     
  8. KM1H

    KM1H Ham Member QRZ Page

    The answer is right on that manual page you posted which is why I used those numbers.

    Hint: Danny's head is almost touching Element 3:D

    Carl
     
  9. KB1ZQ

    KB1ZQ XML Subscriber QRZ Page

    I am going to see about getting the antenna to the ground in the next few weeks and go thru it... I used NOALOX on all the tubing connections and figure it would be good to clean everything up and go from there. I have ordered new caps for the traps. So a tower party is due.

    I do have one other question, does the X-740 (40M add on) work directional when mounted on the X-7... I have the full set up and am asking to be sure... it seems to but not positive...

    Oh, BTW ; I sent an email to MFJ and asked about the differences in the measurements and go "I don't know, we did not own Cushcraft then"... so much for customer assistance from them...

    Thanks
     
  10. KB1ZQ

    KB1ZQ XML Subscriber QRZ Page

    Update - Got looking at antenna and have figured out (I hope) why antenna acts up during the rain... On the front of the antenna are the traps that tune to certain bands... there are 4 traps with 2 covers each on them... total of 8 covers well 6 of the covers are missing... Luckily I have 10 replacements available in my possession. So if all goes well the antenna comes down and gets repaired now and then goes right back up... Bad thing is it is in the upper 40's and is wet with dew... but that is what they make heat guns for... HI HI HI... Also have new coax ready to go onto the antenna as a precaution. Going to be a long day in the air... Got antenna down and was ready to do rapid repairs and ran into a snafu, the caps I bought would not fit... Found out later they needed to be heated and then installed as they expand when heated... Got all 4 traps repaired and ready to reinstall.... checked inside and all is well there. Went thru the Baluns and found the one for the 10-15-20 portion of the antenna was bad (the Toroid was broken), ordered an new one from the Danny should be here by Thursday at latest. So with luck antenna will go back up on Friday...
     

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