EFHW antenna and balun/unun/transformer questions

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KO4HJL, Sep 27, 2020.

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  1. KO4HJL

    KO4HJL Ham Member QRZ Page

    I am a new ham, passed my Technician and General.

    I would like say the words of wisdom, "I am in over my head"

    Before I got my license I purchased an antenna for shortwave listening. I have an 133' wire, 9:1 balun and coax into the house. The person I purchased it from said it should work on transmit when I get my license.

    I purchased a Yaesu FT-890AT yesterday and performed some tests. The internal antenna tuner seemed to work but I don't think I was transmitting with any usable power. Another run of the internal antenna tuner returned Hi-SWR, So I stopped there.
    My NanoVNA also shows effectively infinite SWR. (Tested on 80, 40, and 10 meters)

    So now the question:
    I have been reading about EFHW antennas, seems like I should get a 49:1 transformer to replace the 9:1 balun.
    Am I on the right track?

    Thanks for any advice.
     
    KF5KWO likes this.
  2. KC3PBI

    KC3PBI XML Subscriber QRZ Page

    You've described a bunch of pieces that can be expected to work, but since they don't appear to be working at the moment, I'll suggest that a detail has been missed somewhere.

    The way I understand matching an EFHW is that a 9:1 is a compromise that will get you close enough for the average internal tuner to handle the rest when you are targeting multiple bands. I use one myself on a 147' wire and I think I have acceptable results: the internal tuner struggles on a couple of bands and not at all on others but I get a safe and useful SWR everywhere eventually.

    Have you got that nanovna calibrated and hooked up directly to the unun?
     
    N8ZL, WB5YUZ and KF5KWO like this.
  3. K2WPM

    K2WPM XML Subscriber QRZ Page

    Might be confusing two different antennas.
    An end fed half wave uses 49:1 balun.
    https://elginradio.wordpress.com/2017/10/17/end-fed-half-wave-antennas/
    Your 9:1 balun would be better suited for end fed "random wire."
    Here are some recommended lengths that might give you better SWR
    http://www.webclass.org/k5ijb/antennas/End-fed-multiband-antenna-BalunDesigns.htm
    Also, if you use the "search" function above right, "end fed" will give you lots of prior discussions here. About five pages of threads, some great ideas and info.
    Let us know what you try!
     
    N8ZL, N8TGQ and KC3PBI like this.
  4. WA7ARK

    WA7ARK Ham Member QRZ Page

    Hi David,

    First thing is to understand the difference between two different types of "end fed" antennas. My previous post, here, explains the difference.

    You can make what you have work, but first you have to understand that the "end-fed antenna" you bought is basically a Marconi vertical antenna (expects to be driven against earth) and requires an electrical connection to an extensive "ground system" which just the piece of coax between the transformer and rig is totally inadequate for... The vendor lied, or at least glossed over this requirement!

    The "ideal" ground system for your antenna is a minimum of four radial wires, each ~1/8wl (31ft on 80m, yes, that is 123ft of wire), placed near the earth under the transformer. Electrically, the ground system would be connected to the shield of the coax at the transformer end.

    Lacking that required ground system, in your installation, there is an accidental connection to earth ground through the chassis of your FT890, to the DC supply, out its AC line cord, into the wall outlet and through the house wiring to the electric utility ground. The moment you disconnect the coax from the FT890 and connect it to the VNA, you have radically changed your entire antenna system, and what the VNA sees is nothing like what your FT890 tuner sees...

    So, the ball is in your court. Do you want to fix what you have, or start over????
     
    G6YYN, SM6CJB, KC2IEB and 2 others like this.
  5. KU3X

    KU3X Ham Member QRZ Page

    New ham......congratulations !

    You are also off to a good start. "You are on track !" Yes, replace your 9 to 1 UnUn with a 49 to 1 UnUn. Your antenna is a half wave on 80 meters, full wave on 40 meters and so on. So your feed point impedance will be very high on the antenna's harmonic frequencies.
    A 9 to 1 is mostly used on a non resonant antenna, as stated in the above post.

    Barry, KU3X
     
    N8ZL, WB5YUZ, N8TGQ and 1 other person like this.
  6. KF5KWO

    KF5KWO Premium Subscriber QRZ Page

    It could be that your balun is shot, or that the coax has a short or is otherwise damaged. But yes, from what I’ve read (I want to use an EFHW for 75m), you do need the 49:1 transformer, technically an UNUN and not a BALUN. I would recommend inspecting and testing your coax with a little multimeter, and also inspecting the balun. If it’s enclosed in a little box, just open it up and see what’s in there, could be something is loose, could be it’s just not the right component for your EFHW. The 49:1 transformer is easy to build, or you can find them available for purchase.

    Facebook has a number of groups devoted to ham radio. The “End Fed Half Wave Antennas” group is an excellent resource for EFHW information, plenty of files available there to read, and plenty of encouragement. Check it out! :)

    73 de Jeff, KF5KWO
     
  7. KO4HJL

    KO4HJL Ham Member QRZ Page

    Thanks to all for the responses,

    I lowered the antenna and connected the NanoVNA directly to the 9:1 unun. (raised it back up a bit to run tests)
    SWR off the graph so I need to dig into that.
    The NanoVNA is calibrated and I performed tests on an VHF/UHF antenna so the NanoVNA is reporting good SWR on that.

    The existing unun is in a glued PVC pipe so I will need to cut it open. Additionally, I am going to buy or build a 49:1 unun.

    I have more reading to do. I will follow up when I have my parts and can do some more testing.
     
    KF5KWO likes this.
  8. KF5KWO

    KF5KWO Premium Subscriber QRZ Page

    Looks like you've got some great trees for plenty of antennas. :)
     
  9. KO4HJL

    KO4HJL Ham Member QRZ Page

    Actually I think I do. My existing antenna is fed from the back peak of my house, then to a tall oak in the back corner of the yard. I take about a 100 degree turn to take up the remaining length to my shed.

    I hate ladders...and my kids (teenagers!) dont want me to climb, either. Probably because they would rather play video games than spot for me!

    I could probably build a big square with four trees for corners and not use the house as a tie point at all.

    I am doing this on a budget now but there may be some additional wire antennas in the future.

    I am going to build and put up a couple of VHF/UHF antennas on the house for my HT and scanner.
    With aluminum siding I think I live a bit of a Faraday cage!

    I also need to work on a outside junction/grounding box to mount arresters and bring cables into the house.

    Dave
     
    KF5KWO and KC3PBI like this.
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    The SWR will always be off the graph when you connect the Vna directly to the 1:9 transformer....

    With the Marconi type of non-resonant wire antenna (the kind fed though a 1:9 transformer), measuring the SWR looking into the transformer means disconnecting the coax feedline. With the feedline disconnected, the antenna "system" has no counterpoise (radial system) at all!. It is like pulling the four radials off a 2m ground-plane antenna, and measuring the SWR looking into just the vertical monopole without radials... Half of the antenna is missing!

    The 1:9 end-fed antenna (if it is not connected to a radial field) relies on standing wave current on the coax shield to act as a piss-poor counterpoise. If you disconnect the coax from the transformer, the totally inadequate, piss-poor counterpoise disappears completely..., so the SWR is infinite...

    As I told you in post #4, even if you measure the SWR looking into the coax at the station end with the Vna, the Swr there radially changes compared to what the radio sees because you break the common-mode current path all the way to the house wiring when you disconnect the coax shield from the radio...

    This is all a consequence of not having a proper set of radial ground wires under the feedpoint of the Marconi antenna in the first place. The non-resonant end-fed Marconi you have requires a ground connection; a resonant EFHW Hertz does not... Can I make this point any clearer???
     
    Last edited: Sep 27, 2020
    K7JOE likes this.

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