Sudden high SWR and no resonance on any frequency?!

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K4TF, Apr 28, 2018.

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  1. K4TF

    K4TF XML Subscriber QRZ Page

    Hi all,

    I have a 200 foot run of Heliax LDF4 which runs up a pole 78 feet in the air in the trees and the N-Male connector plugs into a N-F to PL-259 Male ADAPTOR which plugs into a Balun.

    Then I have homebrew 12 wires set up in a multiband inverted vee configuration coming off the balun down to the trees.

    This Antenna was resonant on all of the 6 bands I had it cut to (using a antenna tuner to fine tune the SWR but the MFJ antenna analyzer showed it was resonant by itself ) and was working GREAT until one day all of a sudden it stopped working.
    We did have 2 days of blustery wind conditions. That’s possibly what caused something to break but visually using binoculars to look it looks fine and still intact.
    Now using the antenna analyzer the SWR is greater than 3 to 1 on all frequencies and as I change Frequency the impedance goes from 0 up past 50 back to 0. The antenna is still receiving just fine. Please. Any ideas??? DE K4TF. Bill

    PS: The other problem I have is that access to the antenna is only accessible with cherry picker which I have a company that is a tree company that comes over $200. :-(

    | K4TF |**|**||"___.
    "(@)'(@)" "(@)(@)"****(@)"
  2. AK5B

    AK5B Ham Member QRZ Page

    Time to call the cherry picker and re-do the connector. Ouch!
    K4TF and K7TRF like this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    If you do a wideband sweep with your antenna analyzer, not just in the ham bands but across the HF spectrum, do you see the SWR dropping to a good match (e.g. less than 2:1) anywhere? IOW, if the antenna still has distinct SWR dips but perhaps they've shifted down in frequency and no longer fall in the ham bands. That can happen after a big wind event if the antenna wires have stretched depending on how the antenna is mounted and how much you've allowed for things like tree sway.

    If there's no distinct SWR dips anywhere then perhaps the antenna elements on one side of the balun no longer make a good electrical connection. It's not too hard to receive signals on half an antenna that's up nearly 80' in the air even if the match is terrible but very hard to load a transmitter into something like that. I'd start by suspecting wire stretch after your wind event or something like tree limbs sitting on the wires but you'd probably see that from the ground.
    K4TF and AK5B like this.
  4. NK7Z

    NK7Z XML Subscriber QRZ Page

    I'd look for a broken connection someplace... Wind shakes things around, shaken things oft break. I don't think all the wires would stretch out of resonance enough to cause a total loss of resonance on all ham bands at one, unless you had serious winds, which "blustery" might encompass.
    K4TF, AK5B, ND6M and 1 other person like this.
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    Most likely: connector at top open. Second most likely: Connector at bottom open. Third most likely, a short due to water ingress.

    It would take me about 1min to figure out which is the case using my RigExpert AA-600 by doing a SWR and then a R+-jX sweep from 1MHz to 30MHz.

    Even an Ohmmeter between center pin and shield at the shack end might be instructive.
    K4TF, K7JOE, WB5YUZ and 2 others like this.
  6. KD0CAC

    KD0CAC Ham Member QRZ Page

    I would start over , if the only thing to access working with antenna is " a $200 cherry picker " then something else is called for , to my mind / budget .
    Unless you have a know - in the trees antenna design , almost any in the tree wires break , sooner or later .
    Do not get some of your post , too many adapters and what is N-F - hopefully not a 75Ohm TV connector ?
    It doesn't matter at this point , but " all 6 bands " ?
    K4TF likes this.
  7. ND6M

    ND6M Ham Member QRZ Page

    Dunno what analyzer you have, but most will tell you where any defect is located in the feedline.
    AK5B likes this.
  8. KA5ROW

    KA5ROW Ham Member QRZ Page

    Always put dipoles and such on a pulley system. makes it easy to do repair, and you can lower it ahead of time for a major ice storm.
    WA8FOZ and K4TF like this.
  9. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Good advice. I suspect his heliax run all the way up the pole makes lowering the antenna tough.

    Heliax for a 200' HF run is crazy overkill but heck if you've got the cable.... The OP might consider terminating the heliax run near the base of the pole and running coax up to the feed point. That would allow for some kind of pulley lowering system for maintenance as the flexible coax could easily be lowered.
    K4TF, WB5YUZ and KA0HCP like this.
  10. K4TF

    K4TF XML Subscriber QRZ Page

    First, you’re advice is good. I agree that a better way to access the feedpoint other than $200 ( after reviewing my notes I noticed that he only charged me 150 last time still that’s a lot ) cherry picker but the OL was adamant that the wires be hidden from view of our beautiful wooded backyard so I really did a perfect job of hiding the wires. You can barely see anything. Even the pole is camaflouge green army 4’ aluminum poles. Your q: that’s my Adaptor. The heliax is terminated with a N Male connector. The balun of course has a PL-239 Female connector so I used an Amphenol brand N Female to PL-239 Male Adaptor.

    Thank you for writing. I appreciate the advice. 73’s Bill

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