End Fed Wire - 40m high swr suggestions

Discussion in 'Ham Radio Discussions' started by KC2IEB, Sep 24, 2020.

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  1. KC2IEB

    KC2IEB XML Subscriber QRZ Page

    Hi all - this is my first HF antenna, being new to the lower end of the spectrum. I'm hoping to find some help here improving the efficiency of my antenna.

    I have a 73' wire attached to a Palomar 9:1 unun, far end is roughly 25' in the air hanging from a rope over a tree branch, and it is stretched across a regular suburban yard. Basically as high as I could throw the weight with line to get the antenna in the tree. I have a 15' counterpoise wire on the ground, it's parallel but in the opposite direction of the 73' wire. I have 55' of RG8x feedline coming into the shack, with a 1:1LDG RU-1:1 Unun 200W PEP Coax Choke at the end of the feedline, then a short 3' rg8x jumper to my ICOM 7300. I tried using 100 ft of similar RG8x feedline and the SWR got worse across the board.

    When it works, it works awesome. However, i notice I am challenged to tune 40m, due to high SWR. I included a RigExpert sweep of the antenna, and I'm happy to provide anything else.

    What else can I try, short of an external tuner, to getting onto 40m?

    Thank you so much!

    73 kc2ieb chris
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    What you have there is a venerable End Fed Random Wire.

    You need a tuner.

    More radials will improve performance and make tuning smoother/easier.

    Random Wire: Antenna of whatever length is convenient using whatever materials at hand, installed in whatever manner is convenient.

    The half wave resonant frequency of your antenna would be around 6.4Mhz. However, the 9:1 Balun is going to change the SWR far away from 50 Ohms. That isnt' important for the antenna, though it does increase coax feedline losses. You could try a 1:1 UnUn at the feedpoint to replace the 9:1. But again, achieving 50 Ohms is critical only for your radio output. Get a tuner.

    The ubiquitous MFJ-949e is an excellent low cost tuner that is a swiss army knife of features. It is great for antenna experimenters. Bill.
    Last edited: Sep 24, 2020
    KN6LMF, KC2IEB, K8BZ and 1 other person like this.
  3. W4IOA

    W4IOA Ham Member QRZ Page

    I'd start over with a wire cut close to 66'. Split in the middle and start there. It sounds like you're just adding more and more stuff rather than starting with the correct length.
    66' long, balun in the middle, put it up in the air and try that. I've never gotten too complicated with a simple dipole
    KA4DPO, VK6APZ, W7EDC and 4 others like this.
  4. N3HGB

    N3HGB Ham Member QRZ Page

    I put up an end-fed antenna for 40, it would not reliably tune, took it back down, put up a 40 meter dipole, trimmed it, and it remains rock-solid on 40. FYI
    K4AGO, DU7DVE, N1OOQ and 1 other person like this.
  5. W4NNF

    W4NNF XML Subscriber QRZ Page

    As you've been told, you will need a tuner. Yes, I know, the 7300 has a built in tuner. I have one, and it works well, but I wouldn't call it "wide range." So, an external tuner it will need to be. A manual one is best, since most will have better matching range than the average auto-tuner.
    KC2IEB likes this.
  6. AF2Z

    AF2Z Ham Member QRZ Page

    I've used an end fed wire for years-- no balun, no feedline. Approx 80' length, 30' high; counterpoise under the wire. The ATU in my K3 will match it on all bands 80 through 10. It will work on 160 also but I have to manually set the ATU elements.

    However, I use a homebrew T-match instead of the autotuner because this arrangement keeps the RF from "stunning" my keyboard and mouse on some bands. The T-match consists of two big Dentron caps (500 pF?) and a rotary inductor (35 uH?) from a Collins TCS12.
    Last edited: Sep 24, 2020
    KC2IEB likes this.
  7. AD8BU

    AD8BU Ham Member QRZ Page

    KA9HCP hit the nail on the head... A Random wire with a 9:1 requires a tuner.

    There's a bid of discussion about it in this video:

    If you need to use an end-fed antenna without a tuner, consider an end-fed half-wave with a 49:1 transformer instead of the random wire and a 9:1. Example of a commercial version here: https://myantennas.com/wp/product/mef-330-2k/ or you can find how-to videos on YouTube.
  8. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Simplest solution summary for 40m single band operation with 50Ohm impedance:
    -Shorten wire for 40m half wave
    Math: 468/7.0 = 67 ft.
    -Remove the 9:1 Balun. Feed direct.
    -Option: feed directly, or add a 1:1 Balun at the feedpoint.
    K8BZ likes this.
  9. WN1MB

    WN1MB Ham Member QRZ Page

    For your consideration: https://udel.edu/~mm/ham/randomWire/

    There are "problem lengths" for end fed antennas that are used on multiple bands. Using a 9:1 or 49:1 balun locks the wire into either a match or frequently wicked mis-match to 50 ohms.

    A very basic L-network tuner and appropriately chosen wire length will tune very smoothly on multiple bands.

    P.S. Skip the video. READ.
    WA1GXC and K8BZ like this.
  10. N1FM

    N1FM Ham Member QRZ Page

    This end fed is 63' feet long, includes a balun, and one trap, and needs no tuner.

    There's a Little Elf in the black box and he adjusts the "SWRS" so you can operate anywhere from 40-10 meters.


    However, I think you ought to keep experimenting. Avoid problem lengths like WN1MB said. You'll find the right length eventually.

    An RF choke to prevent using your coax shield as a ground would be helpful.

    Also, height of the wire and the number and length and height of counterpoise, or radials matters.

    I'd give you more info, but you're on the right track. Reading and continued experimentation will teach you more than buying an antenna.

    The MFJ-949e tuner would save you a lot of headaches but the right balun and the right length of wire and counterpoise WILL work.

    https://w6fsb.org/DIY/Random Wire Antennas - Best Lengths.pdf

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