Trim the EFHW wire?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KX4AZ, Jul 18, 2021.

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  1. KX4AZ

    KX4AZ Ham Member QRZ Page

    At a summer QTH I have an 80-10 EFHW antenna (about 135' length horizontal, about 25' AGL), attached to a 50 foot RG8X feedline. I also attached a short (15-20 foot) counterpoise wire at the junction box containing the matching transformer, where the coax meets the antenna provide some future flexibility, should I decide to insert a common mode choke somewhere along the feedline.

    Paired with an ICOM 7300 I have no problem tuning on every major band, and with limited use it seems fine for my simple needs. However, measuring the resonance point dips with a nanoVNA analyzer I noticed that the frequencies are on the low side - suggesting that I may eventually want to trim the line length....

    Band Frequency of lowest SWR
    80m 3.46 MHz
    40m 6.78 MHz
    20m 13.88 MHz
    15m 24.3 MHz
    10m 27.75 MHz

    Anyone care to do suggest how much length I could trim the the wire by to bring me closer to the band centers? And can I shorten the length by simply doubling it up at the end rather than physically cutting it?
  2. K7MEM

    K7MEM Ham Member QRZ Page

    The antenna sounds like a reasonable installation. But the EFHW was never meant to be resonant. It was meant to be used with a tuner. If you can tune it on every major band, there isn't a problem.
  3. K8JD

    K8JD Ham Member QRZ Page

    A big factor for having low freq peaks is closeness to the earth.
    I had a loop I calculated for 7.1 MHz and it only got put up about 20 ft and showed low SWR a bit below the band. I cut about 4 ft to get it to 7.000. I imagine if I could have raised it up to 30 ft It would have done the same freq shift !
    KI4ZUQ and W2VW like this.
  4. KU3X

    KU3X Ham Member QRZ Page

    The idea behind a HWEF is that it is in fact RESONANT on numerous bands. A random length EF using a 9 to 1 UnUn at the feed point is a non resonant EF and it is meant to be used with a tuner.
    I use a 40 meter HWEF when I set up portable and no tuner is needed on 10, 15, 20 and 40 meters.
    I would cut off 3 feet of wire from your HWEF80. Mine is 131 feet 5 inches long and it works great.
    Just for the record, I have numerous HWEF antennas.

    Barry, KU3X
    KD2TJD and K8NIV like this.
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    I see Barry beat me to debunking the idea that an EFHW is not resonant. It is the non-resonant random wire Marconi antenna (the one that is usually fed with a 1:4 or 1:9 transformer) that always requires a wide-range tuner, and has high coax losses because the coax feedline is operated at > Swr = 5 or 6 on some bands. That type of antenna is quite different to a EFHW.

    Actually, if properly compensated, the EFHW actually is resonant on lots of harmonically related bands, and no tuner is needed, as I show in the slide show linked to at the bottom of my QRZ page, and these QRZ forum postings:

    A word of caution, it takes extra effort to make the 8010 antenna resonant on 75m and also on 40m, 20m, 17m, 15m, and 10m. It is easier to make it resonant at ~3550kHz, and then the higher order harmonics line up. View the slide show for details.
    Last edited: Jul 18, 2021
    KD2TJD and KI4ZUQ like this.
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    Ignore... spurious post.
  7. KI5WW

    KI5WW Ham Member QRZ Page

    I have the MyAntennas 7510 2KPLUS endfed. Yes it was designed to be resonant on 75,40,30,20,17,15,12 and 10 meters. I installed with a significant bend at the far end away from the transformer due to space restrictions and metal storage barn metal driveway and patio covers. It actually
    Was pretty close when I completed it. It’s in the inv vee config which is still not the way it was designed to work. I had trouble with 10 and 20 meters which I had to use the auto tuner on the 7600 to tune which it had no problem in doing so. So I emailed MyAntennas to see if we could make this better on those two bands. With e emails I had it where the swr was less than 2:1 across all those bands. No tunner necessary. This guy knows his antennas. First thing he mentioned was that every install is different. That’s why no instructions on paper are avail. I shortened mine about 24 inches and added coax to the feed. Nothing else. He was right, every install is different. Great company. But your install will be different.

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