Tuning my 10-40meter vertical quad wire loop

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI7ELQ, Jul 11, 2018.

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  1. KI7ELQ

    KI7ELQ Ham Member QRZ Page

    I've had this antenna working for the last month; Its achieved my primary goal for usage on 40m/20m bands.

    Its built based on the standard calculations for 7.1 Mhz -> 141 ft. 6.6 inches (43.1 mtrs.) #12 awg coax fed 50% up the vertical leg from a 4:1 Balun (vertical polarization and low angle takeoff) . Top is hung at about 50 feet.
    I tuned its length with my RigExpert minimizing the swr to about 1.1 @ 7.1 mhz.
    14.1 mhz swr is 1.5 - i'm happy with the results.

    I finally got around to running the rig expert software and ran a full sweep from 0-30 mhz and got a better view of the swr over the entire spectrum (if you have a rig expert, this free software is a great feature).
    betterswr.jpg

    It looks like it should perform fairly well on 17m as well, just have not tried it yet.

    My EZNec model predicted minimal swr on 40m/20m/17m/10m but my modeling didn't include the 4:1Balun etc - so the values were between 2.7-6.5 (which is bound to be due to my minimal knowledge using eznec).

    I know that multi-band antenna have tradeoffs so and this one seems fairly reasonable, but I'm curious of the following:
    • If I change the length and move the sweet spot from 7.1 mhz to say 7.3 will the other minima shift .2 mhz?
    • Are there any techniques to improve the swr on the higher frequencies - like 15m/10m? with impacting the low frequency swr?
    • Is it practical to get wider sweet spots on the lower frequencies (increase the Q i think) and thus more room to tune? eg larger wire?
    Bottom line is I'm happy with this one, but its fun to learn and tweek.

    73 JOhn
    KI7ELQ
     
  2. KK4OBI

    KK4OBI Ham Member QRZ Page

    John,

    Modeling gives at 7.1 MHz and #12 awg
    20m 13.7 Mhz
    15m 20.8 MHz
    10m 27.6 MHz

    At 7.3 MHz.
    20m 14.1 MHz
    15m 21.4 MHz
    10m 28.4 MHz
     
  3. KI7ELQ

    KI7ELQ Ham Member QRZ Page

    Thanks! thats very interesting - a 0.2 mhz shift at 7.1, turns into a 0.8 mhz shift at 27mhz.

    I'm going to have to dig into a book to understand why a 0.2 mhz shift at the low band (7mhz) seems to double each step up the higher frequencies.

    John.
     
  4. N7EKU

    N7EKU Ham Member QRZ Page

    Hi,

    It's not doubling, it's 2x 3x and 4x the original change. Hint, read up on harmonics :)

    73,


    Mark
     
    NH7RO, AI3V and KI7ELQ like this.
  5. K4SAV

    K4SAV Ham Member QRZ Page

    SWR is not what you should be looking at. The radiation pattern is what you need to know. A vertical loop fed on a side and used above its fundamental frequency will be a high angle radiator. It will only be low angle on 40 meters. On the higher bands, there should be enough signal left at low angles to make some contacts, but most of the signal will escape into outer space.

    Jerry, K4SAV

    vert loop.gif
     
    NH7RO, WB5YUZ, KP4SX and 1 other person like this.
  6. KI7ELQ

    KI7ELQ Ham Member QRZ Page

    I figured there was a way to get eznec to generate the elevation plot on other frequencies - now to find out how. thanks.
     
  7. K4SAV

    K4SAV Ham Member QRZ Page

    It's very easy. In the main window click on "frequency". A window pops up. Enter the frequency. Click the "Plot Type" button and select 3D to see everything. In the main window click on the "FF Plot" button to get the plot.
     
  8. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    I would not count on working a lot of DX with a vertical loop on any band other than the fundamental.

    I have a "distorted Delta" on 40m fed for vertical polarization. It works very well on 40m for being as lossy as it is (too low), but doesn't work worth a damn on any other band except for 15 and 10m into the Caribbean/South America. I think this is because the loop's distorted shape produces a lobe which happens to be useful in that direction, and this is borne out by modeling. On 20m it is an absolute dog.
     
    NH7RO likes this.
  9. KI7ELQ

    KI7ELQ Ham Member QRZ Page

    Thats been my experience so far. It does ok on 20m to the east cost, and I have no trouble getting Japan/South pacific on 20m using the loop but no luck for europe. I was hoping was that it would be a better receive antenna on 20m for europe, for TX I have a 20m dipole that works slightly better for europe but I just don't hear many signals to work.
     
  10. KK4OBI

    KK4OBI Ham Member QRZ Page

    John,
    To the resonance peaks for your quad for 7.1 and 7.3 MHz,
    lets add the far field radiation polar graphs and 3D views for 40, 20, 15 and 10 meters.

    40m Quad Side-fed on 40&20m.png
    ======================================================
    40m Quad Side-fed on 15&10m.png
     

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