EFHW - what do you do with the ground lug?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AC1JO, Nov 15, 2020.

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  1. AC1JO

    AC1JO Ham Member QRZ Page

    Hi all, first time posting on these forums. I'm looking to build an end-fed half wave (EFHW) antenna as my first HF antenna -- hopefully before we get too much snow on the ground this winter! I'm watching lots of videos (like this one and this one and this one) about how to make the transformer (balun?) and have read G0KYA's instructions. What is confusing me is that some of these guys (like "Radio Prepper") solder the bend in the twisted wire to the shield of the coax, and others (e.g. M0MSN) solder it to a bolt/lug that sticks out of one side of the box. My best guess is that this lug they're installing is the optional ground (earth) path mentioned by G0KYA. My question is, what do you do with that lug when you install the antenna? Wire it to a copper ground stake? Wire it to some other part of the system? This is the missing puzzle piece that I can't figure out from the Youtube videos...

    If it matters, I'm looking at the 20W Xiegu G90 as a likely first HF radio, and I plan to work on some QRP kits over the winter -- so this antenna would not be subjected to very high power at first, but I expect I may get up to 100W in the next couple of years.
     
  2. AC2QH

    AC2QH Ham Member QRZ Page

    What I have for my 148' LW: A 9 to 1 unun at the antenna. The ground lug goes to a heavy #10 wire running straight down to a ground rod with 8 radial wires (random length scrap wire 25 to 50' long) running several inches under the ground. The ground rod is connected by a #6 copper wire to the power entry ground rod (as are all my ground rods). The shield of the 50' coax run back to the shack also acts as a counter poise for the antenna. The coax goes to a 1:1 current unun acting as a RF choke to keep the common mode RF on the outside of the coax from getting into the shack. The coax goes to a lightning protection device (gas tube type) and then to the antenna tuner. I have worked over 100 countries with 100W on this antenna.

    The important things are: 1: A LW has high Z at the feed point, so you need a voltage unun to help match the high antenna Z to the coax and to help the tuner make a match. 2: A LW needs a counterpoise from ground radials and the shield of the coax. 3: A LW must use a current unun choke at the shack end of the coax to stop the common mode RF flowing on the outside of the shield from getting into the shack. Coax wound on a toroid core or a coax W2DU bead choke are appropriate.

    VE3EED offered some good advice on best lengths for a LW use. Here they are (in feet) 29 35.5 41 58 71 84 107 119 148 203 347 407 423 The idea is to stay away from half wavelengths for the ham bands.
     
  3. N8TGQ

    N8TGQ Ham Member QRZ Page

    duplicate
     
    Last edited: Nov 15, 2020
    WA7ARK likes this.
  4. N8TGQ

    N8TGQ Ham Member QRZ Page

    Dont confuse EFHW antennas with "random" wires. An end fed half wave is exactly that-one half wavelength for the band you're using .
    I have built a lot of 64:1 matchers and never use a counterpoise or ground. It never seemed to make much difference. EFHW matchers.jpg
     
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  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    ^This is important to note.

    How to wind the unun and whether to connect an earth ground or not depends entirely on the wire length and how the antenna is installed. There cannot be a single answer to this.

    Many "end fed" antennas are not EFHWs. An EFHW cut to 1/2-wavelength on the lowest frequency of intended operation can be reasonably well matched on the fundamental and all harmonics using a pretty high-ratio transformer. I see Danny at myantenna.com, and he is a well-established antenna designer who did several successful designs for Cushcraft before branching out on his own, uses a 49:1 ratio transformer. 64:1 might be more appropriate, sometimes.

    The 9:1 ratio ununs would be inappropriate for a real EFHW, but might be a great compromise for some random length.

    How they actually perform on the air is based on the same formula as any other horizontal or sloping wire antenna: Higher is better, at getting it at least 1/2-wavelength above ground on the lowest frequency is pretty ideal...but that would be >120 feet high on 80 meters. Most can't do that, so they must live with whatever they get and be happy with it. Even a low wire will make contacts.

    The tuner in the Xiegu G90 seems very good (I have one!) and capable of allowing the transmitter to work at full power into very natively mismatched antennas. As an example, my 80m trapped inverted vee is resonant at about 3700 kHz and its native VSWR at 3500 and 3900 is >5:1 -- the Xiegu matches that just fine, taking maybe 2-3 seconds to find a match. Not bad.
     
    N8TGQ likes this.
  6. W9KEY

    W9KEY XML Subscriber QRZ Page

    I have two EFHW resonant wire antennas. Both use the basic 49:1 transformer, one is for 75-10 meters (MyAntennas.com EFHW-7510-2K), the other is for 60/30/15 meters (home built).
    You normally don't connect that ground lug terminal to anything. Most of the time it can be left unconnected.

    But it is a good idea to install a common mode choke about 10 feet (of coax) away from the 49:1 feedpoint transformer. That 10 feet of coax serves as a counterpoise for the antenna, and the CMC prevents any stray RF from traveling back to your shack (radio). And like all antenna cables entering your home - the coax shield should be "grounded" at the cable entry panel, either with a typical lightening arrestor (or a simple "pass-through" barrel connector) mounted on a grounded copper plate. That grounded plate connection must also be bonded (connected) to your home's service entrance ground with at least a #6 ground wire.

    Nearly everything you need to know about EFHW antennas can be found in this Presentation By WA7ARK.
    Nice video by Steve Ellington on Winding The Transformers.
     
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

  8. AC1JO

    AC1JO Ham Member QRZ Page

    Ok, I hadn't even thought about a "cable entry panel" or lightning protection. Anyone have a link to the "for dummies" version of how to safely run coax into a house? I was basically just planning to disconnect radios from antenna if there was thunder...
     
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    Try watching the "Lightning Slides" linked at the bottom of my QRZ page... A pre-covid hamfest presentation :(
     
    KO4NYR likes this.
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    duplicate post.
     

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