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using an unun and a current balun on the same feed line?

Discussion in 'Home Brew' started by Rusty_831, Jul 27, 2020.

  1. Rusty_831

    Rusty_831 Member

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    hi I was hoping to get some advice from the group on how to impedance match my mobile setup and also use a current balun to mitigate any common mode current. according to my rig expert at resonance my 1/4 wave vertical measures z= 60 j+.01 and id like to wind an unun to match the coax to the antenna but I also want to wind a choke to take care of any common mode current present. can this be done in one enclosure or on a single torrid or does it need to be one separated from the other in series before the feed point . id like to use a single box to accomplish this and mount it at the feed point but im in uncharted territory again and need some assistance please.


     
    Slowmover likes this.

  2. sp5it

    sp5it Master of puppets

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    Z=60 don't bother impedance matching.
    Mike
     
    Slowmover and midnight special like this.
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Z=60 is an SWR of 1.2:1 No need to match it. Leave it alone.
     
    Slowmover, sp5it and BJ radionut like this.
  4. Rusty_831

    Rusty_831 Member

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    great will just use the 1:1 current balun and call it good. thanks for the advice and taking time to reply.
     
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  5. datsun66

    datsun66 Active Member

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    I have the same setup. 4 to 1 balun with an unun on my ocf and talking the world.
     
  6. Slowmover

    Slowmover Elmer

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    I also prefer ununs on my cheeseburgers.
     
    binrat and fourstringburn like this.
  7. TheBlaster

    TheBlaster Active Member

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    I can add a little to this. I am using a 1/4 wave GPA with a 1:1 balun (not strictly necessary but nice robust element/radial connections via eyelets and butterfly wing nut connector on it) as the connection point for driven element and 4 x roughly 45 degree sloping radials, seems to work fine and SWR circa 1.4:1 and could probably trim it up to be better yet if I wished.

    A new semi DIY project I have on when the parts arrive is making a 1/2 wave near ground mounted antenna. So I have a unun 1:64 on its way, to which I will add a 1/2 wave driven element.. the coupler has a counterpoise terminal so I plan to make a ground radial system of 32 x thin wires, fairly short and manageable and should make it quite efficient without being too impractical.

    I am getting a bit tired of the GPA radials impracticality (takes up space restricting some portable locations) so want to opt for something improved whilst keeping the current centre in the same place above the ground which the 1/2 wave should do.

    I will let you know how I get on with it once built and tested.

    This video inspired me...(although I am going to forego the stub match) I am hoping to get an ok match by just adjusting/trimming the radiating element against the ground plane radials..

     
    #7 TheBlaster, Dec 4, 2020
    Last edited: Dec 4, 2020
  8. TheBlaster

    TheBlaster Active Member

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    I can confirm my 1/2 wave works nicely.

    SWR is 1.2 - 1.4:1 across band of interest.

    I made a 2 x 3,500 mile contacts using 10 Watts radiated, and many other 800 - 1,500 mile contacts. I cannot conclusively say it is better than the GPA but it is at least as good and is easier to erect. I am satisfied with it.
     
  9. binrat

    binrat WDX Club Coordinator
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    I use EFHW portable all the time as my primary SOTA antenna, no radials. Very fast to setup and works well. Early Nov I had 24 contacts in 17 minutes, 9 EU stations with about 50 watts. Normally run 10-12 watts depending on the battery voltage with consistent contacts.
    Attached a map with my activation last week.
    idlewilde contacts.png
     
  10. TheBlaster

    TheBlaster Active Member

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    Nice, yes worked a fair chunk or Europe from the U.K. (Moscow and Greece being my 2 most distant contacts) and my first contacts outside of the continent today. It is a decent start. No such luck for me with many contacts in a short time, 2-3 per outing seem typical so far, the only 2 contacts today to Canada (New Brunswick and Ontario). Had my foundation licence for about 6 weeks now, most contacts made on 20m.
     
    #10 TheBlaster, Dec 15, 2020
    Last edited: Dec 15, 2020

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