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Look ma, no counterpoise! An evaluation of a EFHW-8010

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA7ARK, Apr 24, 2019.

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  1. AI3V

    AI3V Ham Member QRZ Page

    Thats what I figured Brian, personal insults instead of proving with a actual ,reproducible public demonstration the merits of your claim.

    Rege
     
  2. AI3V

    AI3V Ham Member QRZ Page

    Same to you professor, let me know when you want that altoids tin.

    Science be scary yo

    Rege
     
  3. AA5CT

    AA5CT Ham Member QRZ Page

    Objective tests - did I miss the posting of an objective test?

    Interested parties would like to know ...
     
  4. AH7I

    AH7I Ham Member QRZ Page

    Does the voltage vary by very close to the same amount at either side of the feed point?
    Essentially the shield is also "end fed".
     
  5. W5DXP

    W5DXP Ham Member QRZ Page

    The voltages follow Ohm's law and can be quite different when using a current balun to balance the currents.
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    All you can say about any antenna is that there is a voltage between the terminals at its feedpoint. Since the feedpoint is not at the center of a dipole, there is some voltage relative to earth on the coax shield right below the transformer. That is the source of the common-mode current in the coax shield, which can become large if the coax is allowed to resonate.

    Yes. If there is no CMC on the coax, the coax can become a resonant, radiating conductor in its own right. One way is that it is a multiple of a 1/2wl if the rig end of the coax is not grounded; (if resonant, it become a Hertz radiator), or a multiple of a 1/4wl if the rig or the rig end of the coax is grounded; (if resonant, it becomes a Marconi radiator).

    If the average ham grabs a random length of coax that happens to avoid either type of resonance in the coax, then the coax acts as a "counterpoise", and the user is happy. There is relatively low probability that the user happens to pick a length of coax that does resonate on the frequency where the antenna is used, so in most EFHW installations, the CMC doesn't seem to do much, but putting one there prevents the unwanted resonance on any frequency...
    Putting one there defines the coax between the transformer and CMC acting as the "ideal length counterpoise".
     
    Last edited: Jul 23, 2019
    G5TM and K0UO like this.
  7. K6BRN

    K6BRN XML Subscriber QRZ Page

    Yes, you did. And the paper that went with it. Both you and Rege, apparently. Not to worry. if you back through the threads (and there are a LOT of them), you'll eventually find it. But at less than $200 (chickenfeed) including paracord, eye hooks, etc. you can do your very own tests, from your very own point of view. Which, i think, is ALL that's left to wonder about.

    Have fun!

    Brian - K6BRN
     
  8. KX4O

    KX4O Ham Member QRZ Page

    My simulations of a 2m EFHW agree with your comments...
    [​IMG]
    Guess I should remake the graph with wavelengths along the x axis.

    My Diamond K515 mount's 13.5 foot cable length seems to agree (at least in theory)...
    [​IMG]
     
  9. N4RL

    N4RL Ham Member QRZ Page

    Thanks to all for the excellent information found in this thread.

    I have recently replaced an OCF dipole with 80-10m EFHW on my small city lot. The dipole required creative routing of the legs with a fair portion of its length just a few feet above my 2nd story roof. I was never very successful or happy with this dipole. The EFHW is able to be deployed on my cramped lot without being strung over my roof, with about half of its length as a sloper and the other half roughly flat, running between two trees. I seem to be having much more success with the EFHW, regularly being heard and being able to hear other stations, including stations at greater distances than were worked using my dipole. I suspect this mostly has to do with the limitations I had in deploying an antenna on this tiny lot, and finding an antenna that better matches my deployment capabilities.

    It hasn't been all roses. I have also noted a regular increase in noise, above what I had come to expect using the dipole, which has forced me to learn to use more of my transceiver's noise taming features.

    My operating position is a second story bedroom, 15' above earth. I am planning to run a 2" copper strap from a ground rod directly below which is tied into the mains ground a few feet away. I will ground the EFHW at this point and then pass the strap through a window where it will take a sharp 90 degree turn for about 6 feet before connecting to all of the 1" mesh ground straps of various lengths from my equipment. I hope that in spite of the distances described, I will get some RF grounding benefits. I would be delighted to see some reduced RFI on 80 and 40 meters, but I am expecting no RF ground at all on 20 meters due to the distance being about 1/4 wave.

    I know there is a thread here specifically for grounding, but I thought I would mention my situation here in case anyone has any specific comments related to grounding of the EFHW as I described.

    Thank all.
     
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

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