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. WA7ARK

    WA7ARK Ham Member QRZ Page

    I am creating a presentation on "End Fed Half Wave" antennas which will be one of the tech. forums at the upcoming Prescott, AZ Hamfest on May31 to June 1, 2019.

    As part of my research for the talk, I obtained a MyAntennas.com EFHW-8010-1K and put it up temporarily to run some tests on it. I hung the driven end off the side of my tower, with the transformer suspended with about 8ft of Polyester rope, at about 38 ft agl. The other end of the 130ft long antenna is also about 38 ft agl, hanging in a slight catenary curve, so I guess the middle is about 35ft agl.

    I am using 58ft of foam RG8 to reach the IC7300 rig in the shack. I purposely let the coax dangle straight down, parallel to the tower, several feet from the tower leg, and just ran the other end into a window. There is no Ohmic contact between the coax shield to my tower or building ground except at the rig end. The coax does not touch the earth. I did this so I could check to see if any common-mode RF-induced problems happen in the shack...

    Here is a picture of the test set up: (click on pictures to enlarge).
    EFHW8010test.png

    I then used a RigExpert AA-600 to sweep the Swr50 on the 80m, 40m, 30m, 20m, 17m, 12m, and 10m bands: First is a wide sweep from 3.5 to 30MHz. The yellow stripes are the bands, more or less. I also show the Swr plots of each band:
    swrAll.png
    swr80.png swr40.png swr30.png swr20.png swr17.png swr15.png swr12.png swr10.png
    This antenna is basically a resonant half-wave 80m dipole. Since the feedpoint is close to one end of the wire, unlike a center-fed wire which will support standing waves only on odd harmonics, this one will support standing waves on all harmonics, both odd and even. Unfortunately, due to end effect, the frequency progression from harmonic to harmonic is not exactly an integer, but is more like 2.15, 3.15, etc.

    This is normal behavior for any uncompensated "multi-band" antenna that has harmonic standing waves on it. You can move its resonance to a particular spot on its fundamental frequency, but then it will be higher than you want it on all the harmonics. You can tune it to land on one of the harmonics, but then it will miss the band completely on its fundamental and likely also on some of the other harmonics.

    This antenna is equipped with a resonance compensation coil to improve the alignment of the swr nulls on the harmonic bands. It is 6turn coil about 6ft down the antenna wire. It can be seen in the first picture. The swr plots above are a good indication that it works.

    The compensated antenna is usable with the IC7300's internal tuner from 3.5 to 3.82Mhz. I didn't try the "emergency" mode of the tuner. The entire 80m band is reachable with an external tuner.
    The entire 40m band is usable without the internal tuner.
    The 30m band is usable, but only with an external tuner.
    The entire 20m band is usable without the internal tuner.
    The entire 15m band is usable without the internal tuner.
    The entire 17m band is usable with the internal tuner.
    The entire 12m band is usable without the internal tuner.
    The entire 10m band is usable with the internal tuner.

    Next, I connected the antenna to my IC7300 through a coax relay that makes it possible to compare received signals by rapidly switching from one of my regular antennas to the antenna under test, in this case the EFHW.

    Tuning around on 40m, I noticed that the antenna works as you would expect any horizontal wire dipole to work at ~38ft agl. On 40m (the only band I could do rapid switching between a 40m dipole or 40m vertical and the EFHW, some signals were stronger on the dipole, some stronger on the EFHW, likely because the dipole is erected E-W, while the EFHW is erected NNE-SSW. The dipole is a bit higher at about 50ft agl.

    Transmitting at 10W CW, I watched my signal at KFS (west coast WebSDR) and at UtahSDR (Northern Utah WebSDR) and as expected, sending alternating dits and dahs, the dits being transmitted using the dipole and dahs being transmitted using the EFHW, at KFS, the EFHW beat the dipole by about 6db (off the end of the dipole, broadside to the EFHW), while the opposite happened at Utah.

    Both KFS and Utah have graphing S-meters (kind of like an old strip-chart recorder) which make comparing two antennas easy. My home-brew microprocessor-controlled keyer/antenna switch helps, too. It sends the dits/dahs faster than QSB varies the received signals, so it is easy to sort that out.

    Next, I tried a few SSB calls on 80m, 40m and 20m at 100W, asking for comparitive subjective reports while switching between antennas. Most subjective comparisons are not conclusive, especially if the two antennas are very similar in performance. All I can say is that the two antennas are similar enough that most folks would not notice a difference... A dipole is a dipole is a dipole...

    All the while, I was looking to see if there was any RF coming into the shack to screw with the ALC metering on the IC7300, or to distort the transmit audio, or the computer plugged into it with a USB cable. I purposely didn't install a Common-mode choke on the coax from the EFHW, nor did I connect an explicit ground to the coax. The only ground connected to the IC7300 is the regular station grounding system, where the IC7300 picks up a ground through the black wire of its power cord.

    No RF burns, or other RF related issues, so if there is common-mode current on the coax, there is not much there. I plan to do some more extensive measurements using a current transformer, but that will take some time to set up.

    All in all, a very good first impression. More to come as I do some more evaluation, modeling, and possibly some optimization (I have an idea on how to improve the swr on some bands).
     
    Last edited: Apr 24, 2019
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  2. KD6RF

    KD6RF Premium Subscriber QRZ Page

    Thanks for a good test Mike, but why on earth give the thread such a misleading title?

    One of the biggest problems in developing the understanding of this type of antenna was to overcome the silly notion that it has "no counterpoise".
     
    AG5DB, AK5B and AI3V like this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Well for Rege, ofcourse.
     
    KM1H likes this.
  4. KD6RF

    KD6RF Premium Subscriber QRZ Page

    Yes I thought so, but it probably does a dis-service to everyone else :( For some weird reason, there used to be a common belief that there actually was "no counterpoise".
     
  5. SM0XHJ

    SM0XHJ Ham Member QRZ Page

    If you want to test an "End Fed Half Wave" without counterpoise, why test it _with_ a counterpoise? You have at least 58 ft of counterpoise in that setup.
    Why not suspend the antenna like you have done (the 8 ft of polyester rope is good), but use a small battery operated transmitter directly connected to the transformer instead. A crystal oscillator hooked up to a 9 V battery would do.
    Then, instead of measure SWR and guessing things about common mode current, use a receiver connected to a reference antenna, say an inverted V (which is easy to erect and fairly omnidirectional) some 300 ft away. When you have collected a set of signal strength measurements, change out the EFHW for a center fed dipole of the same size and measure the signal strength again.
    Such a test would actually show something about how the EFHW performs without (or at least with very little) counterpoise.
     
    AH7I, YO3GFH, AK5B and 2 others like this.
  6. W9XMT

    W9XMT Ham Member QRZ Page

    It should be recognized that on the ham bands above 80 meters, the "EFHW 8010" ...
    • is not a half-wave antenna, and
    • has radiation patterns with progressively more lobes and nulls
    ALSO and as shown in the graphic below, without some means of suppressing r-f current flowing on the outer diameter of the shield of a coax transmission line feeding it, this design uses that path as a 2nd conductor of that antenna system — adding radiation to that of the long, horizontal conductor assumed/promoted to be "the antenna."


    [​IMG]
     
    Last edited: Apr 24, 2019
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  7. W9KEY

    W9KEY XML Subscriber QRZ Page

    Nice report, Mike - thanks.
    For some reason yet to be discovered, I just started having common mode problems with the 40 meter (only) part of my 80-10 meter fan dipole (no balun), when running power (~750 watts). Experimentation today pretty much eliminated my headphone interference by using an FT-240-43 toroid with ten turns of RG-8x in the shack, just after my tuner. So, I'm sensitized to common mode issues right now .....

    So what will happen to the performance of this EFHW-8010-1K when adding a good CMC (perhaps like the My Antennas CMC-130-3K) either directly at the antenna feedpoint network box, or (alternately) about 75-100 feet back toward the shack, at the house coax entry panel shield ground point / lightening arrestor? Or I suppose, even adding the CMC all the way back inside the shack, although I doubt that would be recommended?

    Being a new ham, I'm still learning. So guess my question is really aimed at determining if use (and then specific location) of a CMC will mess with the coax counterpoise effect and detract from operation of antennas like the EFHW-8010-1K? I'm considering the 3K version of this antenna, thus wondering what happens if a feedline choke or balun is used.
     
  8. G5TM

    G5TM Premium Subscriber QRZ Page

    A misunderstood and underrated antenna. Thanks for a detailed look at it. 73
     
    MW0HRD and W0AQ like this.
  9. AI3V

    AI3V Ham Member QRZ Page

    Because then it would be brutally obvious that it's just a really expen$ive random wire....

    Rege
     
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  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    Have you ever seen a random wire that has the multiband SWR50 plots I measured and posted as #1 in this forum thread?
     
    MW0HRD, K9AXN and G5TM like this.

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