1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice

My 9:1 un-un has developed a dead short.. ughh

Discussion in 'Amateur Radio Antennas' started by PA770, Aug 18, 2018.

  1. PA770

    PA770 W9WDX Member

    Joined:
    Jun 29, 2016
    Messages:
    569
    Likes Received:
    237
    I have a 9:1 I bought on EB about a year ago and I guess it got moisture in it.. I got a dead short at the SO-239..



    This sucks and I only.found when running new coax to the new shack.. and yes I tested the coax 3 times before I realized and tested the 9:1.. ughh.. glad my meter has a tone on it..

    IMG_20180715_112557153.jpg
     

  2. The DB

    The DB Sr. Member

    Joined:
    Aug 14, 2011
    Messages:
    1,702
    Likes Received:
    795
    Depending on the design, many if not most 9:1 ununs have a DC short between all connections. This is not necessarily a problem as RF is not DC and does not follow DC rules.


    The DB
     
    Captain Kilowatt likes this.
  3. PA770

    PA770 W9WDX Member

    Joined:
    Jun 29, 2016
    Messages:
    569
    Likes Received:
    237
    So your saying I may be ok??

    How would I know?? I mean I get a short on the opposing sides of the unit as well.. one on the antenna side and one on the counterpoise lug as well..

    I can't open it's sealed.
     
  4. The DB

    The DB Sr. Member

    Joined:
    Aug 14, 2011
    Messages:
    1,702
    Likes Received:
    795
    The first thing I would do is put a 450 ohm resistor across the antenna side of the unun and then see how well it matches up with an SWR meter. This is essentially putting a dummy load across the output of said unun matched for what the unun is supposed to convert the impedance to. I doubt SWR will be a perfect 1:1 for various reasons, but it should still be close. Just don't exceed the power of the resistor by to much during this test.


    The DB
     
  5. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    1,911
    Likes Received:
    1,336
    Your'e measuring DC resistance.

    The impedance of a balun only applies to the RF signals that pass through it.

    Not the same thing. It's a transformer, of a sort. And DC measurements of a transformer winding can tell you only one thing. That none of the internal connections inside it are broken.

    That's a good thing, right?

    Takes an RF instrument like a SWR meter or antenna analyzer to see what it is or isn't doing.

    73
     
  6. 543_Dallas

    543_Dallas Sr. Member

    Joined:
    Jul 25, 2011
    Messages:
    1,668
    Likes Received:
    1,689
    The 450 ohm resistor test will show you if something is wrong with it. Your new a99 antenna also has a dead short. ;)
     
    Captain Kilowatt likes this.
  7. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    1,911
    Likes Received:
    1,336
    For DC measurement, but not for RF.

    You hope.

    73
     
  8. 543_Dallas

    543_Dallas Sr. Member

    Joined:
    Jul 25, 2011
    Messages:
    1,668
    Likes Received:
    1,689
    Yes. Thanks for clearing that up again.
     
  9. PA770

    PA770 W9WDX Member

    Joined:
    Jun 29, 2016
    Messages:
    569
    Likes Received:
    237
    Ok. After some thought I thru the coax back on and fired up the HF.. all is well.. the deadshort thing I guess was what you folks said.. a DC thing, not RF. Got my normal SWR tunings for 80/40/20m bands.

    Thanks to all
     
    The DB likes this.
  10. PA770

    PA770 W9WDX Member

    Joined:
    Jun 29, 2016
    Messages:
    569
    Likes Received:
    237

    Just checked.. yes A99 has dead short using an ohm metee.. so guessing that is normal??
     
  11. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

    Joined:
    Aug 25, 2015
    Messages:
    736
    Likes Received:
    572
    Yes. It’s normal. Mine showed the same thing before I put it up, was fine when I checked it with the analyzer though.
     
    PA770 likes this.
  12. PA770

    PA770 W9WDX Member

    Joined:
    Jun 29, 2016
    Messages:
    569
    Likes Received:
    237
    All is well. Just checked swr.. thanks
     
  13. M0GVZ

    M0GVZ Sr. Member

    Joined:
    Oct 18, 2011
    Messages:
    1,380
    Likes Received:
    735
    And on the Imax 2000 there's a capacitor in the middle section so testing with an ohm meter it shows open circuit. There are a lot of people who have needlessly thrown away a perfectly working Imax 2000 or bought a replacement middle section because they just went on the fact the multimeter showed no connection between the ends. However if you used an analogue meter and knew what you were looking at it would be immediately obvious there was a capacitor there as you saw the needle spike on initial contact.
     
    Shadetree Mechanic and The DB like this.

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!