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Shortened End Fed Calculations Help

Discussion in 'Amateur Radio Antennas' started by tba02, Sep 19, 2016.

  1. tba02

    tba02 WOOF

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    I am working on an end fed (faux half wave) antenna for 75 meters (3.9 MHz is my target frequency).
    I currently have one of these - http://myantennas.com/wp/product/efhw-8010 which is basically a 7:1 unun - that I want to use for a single band antenna.

    I have successfully used ~130 feet of wire with the unun in the past, but now want to use it within a space the only allows for ~60 feet.
    I basically want to use the 7:1 unun attached to a 60 foot coil loaded wire that will represent 1/2 wave on 75m (120 feet).

    If I go to http://www.k7mem.com/Electronic_Notebook/antennas/shortant.html I can get various figures for the lengths, coils and spacing, but I have a qaundry. Should I use the figures generated by entering 3.9 MHz and 60 feet, select value A (overall length of a half wave dipole), which is B+C x 2 and use 2 coils, or should I use 1.95 MHz and 120 feet and just use B=C and a single coil?



    Any thoughts on the above or any other suggestions with regard to making a ~60 foot wire look electrically like ~120 feet?
     

  2. Road Squawker

    Road Squawker Sr. Member

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    that program is for a center fed antenna.

    do some research on the end fed zepp antenna,.............. you WILL need to work it "against ground"

    good luck,... 60 feet is really minimal,... can you stretch it to 65? or raise one end to get a longer wire in the same space?

    ,.... it doesn't have to run in a straight line (as far as the antenna i concerned).
     
  3. tba02

    tba02 WOOF

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    60 feet is pushing it already. I can extend it to 65 ft if the last 5 feet drops vertical.
    I have the ground side setup.
    I gues another way of phrasing it is I am looking to configure an EFHW for 75m using 60 feet of wire and coil to present 120 feet to the unun.
     

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  4. vkrules

    vkrules Sr. Member

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    about 190 UH. 45 feet from feed .
     
  5. Road Squawker

    Road Squawker Sr. Member

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    I just re-read this and noticed the 3.9 MHz target.

    that is doable
    32 feet of wire then 44 uH coil, then 32 feet wire should be about 3.6 MHz
    31 1/2 feet of wire then 42 uH coil then 31 1/2 feet should be about 3.8 MHz

    so, 31 feet even should be about 3.9 MHz +/- YMMV

    the coil should be 20 turns 14 ga wire on a 4 1/2 od pvc tube for 44 uH
    .... if ya really wanna be picky, make it 19 turns,... about 40 uH

    that 62 foot overall should fit nicely in the 60 foot dimension with a little sag.
     
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  6. tba02

    tba02 WOOF

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    Thanks, that was similar to what I was thinking but I needed some support. I will give that a try and see what happens.
     
    222DBFL likes this.
  7. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    inverted L and work it against ground radials, at least 24 ground radials, it will work for ya , you hang it vertical at least high enough to walk under and be safe so no one can touch it, then the rest of it run horizontal
     
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  8. 222DBFL

    222DBFL Sr. Member

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    I've been hearing more about L shape orientation and how it can be used both locally and for DX. Not far locally, but locally as in a few miles maybe?? Or am I off here as well or reading things that are incorrect?? The vertical part of the L would give some vertical polarization and the horizontal will give you the horizontal polarization. Am I close here or is this just to me able to hang the amount of wire needed for a long wire type antenna. I could possibly do a horizontal L configuration, I have 3 trees that would work perfect for that. A 9:1 unun balun would be needed correct for use with 50ohm coax? For both RX and TX purposes? Or could one just hang the wire desired, feed it off center and use it as a receive antenna only. Would this work as well or would the 9:1 unun, make it correct for use with 50ohm coax?? I can get the wire figures I want, but would like to hear some input on the L Type configuration. Using one side, the short one, I think, hung vertically or to string the entire wire out horizontally, long end pointed E/W and vertical pointed N. This would mean the E/W portion would place the ends at a N/S orientation and the vertical would be on the pointed E/W for a small window of N/S activity depending on the length of the wire or is that incorrect?? This would be horizontal obviously. Having one end hung vertical would give a more omnidirectional pattern to that end? Yes/no?? I am just curious here gents and not trying to hijack a thread. More curious as to how this type orientation works both ways, vertically and horizontally. Sorry tba02. Not trying to hijack your thread!! Appreciate any responses, and if needed I will post this somewhere else or the mods can delete it if they feel deemed to. Again, just curious as to how things work. It's how some of us learn I suppose. Thx and to all, have a good day!!
    73 and God Bless!!
     
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  9. LeapFrog

    LeapFrog Wielding Hanlon's Razor

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    I think it would work just fine for local talk or DX, all depends how high up it is (jmho).

    Quoting WavRider: "inverted L and work it against ground radials, at least 24 ground radials".
    You are going to need ground radials for a counter-poise to work against the radiating element, many radials.

    Also maybe an antenna tuner depending on your wire lengths used, the balun, and the other "maths" that are involved.

    If the radio wants to "see" 50 ohms, and you use a 50 ohm coaxial feed line..
    Then you would use a bal-un balanced / unbalanced.

    I haven't yet read the ARRL antenna handbook, and I may be incorrect some places in this small post, but I hope that helps a little 222. Never know if you don't ask/read.

    -Leap
     
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  10. 222DBFL

    222DBFL Sr. Member

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    I got it Leap, I have the radio, as my IC746 does have a tuner built in. I just need to figure out what length of wire I will use. This will be for listening only, so i am not in any rush or needing it now. I have plenty of wire and can build my own balun if needed. Just wanted to see wha some that have used them in the different configs would say. I'll research it myself and will get my answers!! I am not one to ask to be spoon fed that is for sure!! I like to get my learn on. Just helps sometimes when someone else may know the answer. Like I said. I get the gist of it. Would more like some confirmation that what I was saying was indeed correct. I'll find out and figure accordingly!! Thx for the replies though man!! Much appreciated!! Hope all is well and have a good one.
     
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  11. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    http://www.hamuniverse.com/slopinginvl.html

    If you going to shorten it with loading coils then adjust your length, trial and error there,
    if only for SWL then it really does not matter if resonant or not if you going to use it for multi band.
     
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  12. Road Squawker

    Road Squawker Sr. Member

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  13. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    I can tune my antenna and get S9 +20 noise on 75 meters, then I detune it and the noise floor lowers and I hear signals.

    I use 40 meter dipole for receive on 160 meters, not resonant.

    I agree resonant antennas do make a difference, but not that important for SWL, hell my little 20" antenna on my truck receives real well and it is no where near resonant from 500 kHz up to 108 mhz.

    ( Copy and paste from link you posted)
    RE: Resonant Listening Antennas -- Why?
    by AA4PB on April 8, 2013 Mail this to a friend!
    Receiving is all about signal to noise ratio. If most of the noise is generated outside of the receiver (as it is on most HF bands) then matching the antenna system to the receiver increases the signal and the noise by the same amount so you have no change in the signal to noise ratio. Thats why the mismatched random wire works so well on HF receivers and impedance match is not so important in that case.

    Thanks for the link. interesting reading especially the magnetic loop antennas.
    To resonant or not to resonant??
     
    #13 wavrider, Sep 24, 2016
    Last edited: Sep 24, 2016
  14. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    I read that link before and thought the part about signals being reflected off into space was lame then and I still do. For simply listening there is not great benefit to tuning an antenna to resonance. Sure lots of people will say how dead their antenna is when the tuner is way off resonance but what is happening is that the tuner is actually attenuating the signals when off resonance. Tune an antenna to resonance with a tuner and then simply bypass that tuner and the results are far less dramatic. I started as an SWL'er about 40 years ago and ran everything for an antenna from a short loaded vertical in an apartment to a 600 foot longwire and when using a tuner only ever saw a small increase in signal but there was also a small increase in noise levels as well. The greatest difference was when using a really short antenna on the really low frequencies like AM broadcast band or even longwave. I had a home made tuner that would tune as low as 200 KHz. Even then the difference was only a couple S-units at best but with a corresponding increase in noise.
     
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  15. 222DBFL

    222DBFL Sr. Member

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    Thanks much for all the replies gents! Think I have in my head anyway what I would like to do. Now it's time to put in on paper and build it and hang it. Again, thx for all the responses and it's greatly appreciated!! Good day to all an here's to hoping all have a great weekend!!!
     
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