Wondering why this antenna isn't more popular....

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC3RN, Feb 8, 2019.

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  1. KC3RN

    KC3RN Ham Member QRZ Page

    The G7FEK:
    http://www.g7fek.co.uk/news.php?page=80m_Antenna_for_small_gar_49493

    I built one last weekend, and works really well. It's a really attractive alternative to the more common G5RV Junior.

    1. Very inexpensive to build.
    2. Works well on 40 and 80, tunable to about 1.1:1 SWR pretty easily. Decent performance on most other bands.
    3. 20m performance easily improved by adding the additional element.
    4. Small footprint.
    5. Not too ugly once its in the air.

    Anyone else using one?
     
  2. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    What other antenna have you compared it with?
     
    KU3X likes this.
  3. KC3RN

    KC3RN Ham Member QRZ Page

    At this point I've compared it with a G5RV Junior, an EFLW, and an MFJ loaded dipole (the 40/20 model). It's comparison to the G5 is what led me to investigate this in the first place. The G7 is mounted in the same position as the G5 and dipole, but not as high. The G7FEK is really designed to be ground mounted (non-elevated radials), so it's about 10' lower than the G5 or dipole were. Eve with the lower height, I get better a response rate.

    I tried several times (with the other antennas) to work South Africa, with no success. I was successful with the FEK. This was on 40m. The dipoles had a pretty high take-off angle at 35'. The FEK has a lower angle.
     
    N0TZU and KC8VWM like this.
  4. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    The trick appears to be how the ladder line is connected to the coax....both sides to the center conductor.
    How is the coax laid out in relation to the two overhead conductors? Since it calls out a specific length of coax I wonder if the physical layout is critical.
    The other trick in the diagram shows a wire connection to the coax outer conductor run to an insulator. What is the length and position of this conductor in relation to the overhead conductor and the coax? A physical layout in addition to the schematic would help.
    I'm using a loaded dipole (40/20) at the moment and it is performing better than a 40/20 unloaded dipole in my yard. I think it's because the full size 40m dipole was extending under some trees in the common area beyond my yard. I've found keeping a distance from the house or the trees is a key factor in antenna performance.
     
  5. K8JD

    K8JD Ham Member QRZ Page

    Looks like a fat vertical with top loading !
    Using a tuner to a low SWR does not make it actually work any better, just makes the transmitter happy.
    I used a tuner to load up a metal window frame, on 20M, at a shop I worked at and worked France during a demo of my new TS520 radio.
     
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  6. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    Oooops....I found the construction details!
    Negatives which impact my physical space laundry reel antenna.JPG
    1. Construction detail says to avoid sloping installation.
    2. Vertical section to avid trees or residence.

    In my yard and with stealth requirements I can't erect a permanent vertical structure in the yard so I'm limited to the residence or the trees. Mounting my dipole counterpoint under the eaves works best. The vertical is my coax.

    Running a dipole out under the eaves resulted in an easy match but poor results.

    Sloping the dipoles down and out to bird feeder stanchions resulted in best performance to date. But it's temporary...see above shown with pole in the lower position.

    During the summer months I sometimes erect a tripod mounted pole used for portable operating mid way between the house and the treeline in my back yard with a sloping inverted vee. This has offered the best performance to date for me.
     
    Last edited: Feb 8, 2019
  7. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    QUOTE
    As no two antenna modelling programs give the same results and it is not possible to model all parameters, computer modelling of antennas only allows for a proof of concept.
    Unquote

    Sigh. Another "This antenna can't be modeled".

    We have previously discussed this antenna. It is basically an asymetrical "T" antenna worked against a radial.

    The ladder line is shorted, so it acts as a slightly fatter vertical element.

    The author offers all sorts of alternative configurations with additional radials, buried radials, slightly raised radials, different radial lengths, different vertical element sizes, unconnected reflective wire elements laid under the horizontal section. Yes, it becomes a chore to model since he cannot commit to any particular design! ;) This isn't an antenna design, it's a mish mash of ideas to fiddle with.

    -No engineering here; cut and try. Amateur radio regresses 100 years.

    In the end the author, himself, states it works about the same as a dipole of the same size and height!!!! Put up a dipole, balanced line and buy a tuner and be done with things. :)
     
    Last edited: Feb 8, 2019
    KD6RF, WD4IGX and NH7RO like this.
  8. KC3RN

    KC3RN Ham Member QRZ Page

    Sort of. I's actually a "nested marconi". The construction is similar to a fan dipole. Both halves of the ladder line are connected to the center conductor of the coax. The coax shield et connected to the counterpoise wires. The wires connected to the top of the ladder line form two inverted "L"'s. Each half becomes a 1/4 wave radiator for 80 amd 40. The addition of a 16.5' radiator to the feedpoint is simply a 20m quarter wave vertical sharing the same feedline.

    I get a match of under 1.5:1 on 80, 40, and 20, so I don't use a tuner there. Other bands require a tuner to make the transmitter happy.

    The antenna has performed very well for me on 80 and 40. 30 and 20 have been okay, but my 84' end fed is a bit better on 20, and no tuner is needed there. I haven't used it on 15, but my meter shows an SWR of about 2.5:1. Tuner required, but an easy match. I haven't tried it on 12 or 10, and I don't operate 160.
     
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  9. KC3RN

    KC3RN Ham Member QRZ Page

    Yeah, no thanks. Been there, but bringing balanced feeders into the shack is a PITA that I'd rather not deal with. Plus I got tired of the antenna impedance changing every time it rained (which is does a LOT here...).
     
  10. NH7RO

    NH7RO Ham Member QRZ Page

    I suspect the vertical component is the main (or perhaps only) reason why this antenna enabled the OP to work South Africa.
     
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