Halfsquare antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 2E0TWG, Mar 21, 2019.

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  1. AF7ON

    AF7ON Ham Member QRZ Page

    What G3TXQ suggested was to maintain the feed at one top corner, but to use the coax shield as the vertical leg on the driven element. In that case, the center of the coax would feed the horizontal wire and the second vertical wire and the coax from the feed point would be the quarter-wave vertical element on that end. It's a very sound suggestion and eliminates the problem of how to run the coax from the elevated feed point.

    Mike
    AF7ON
     
    SM0GLD, 2E0TWG and WB5YUZ like this.
  2. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    With the usual exception; if I've done the modeling right, a 40m one should still have a useful pattern on 15m, something close to 6 dBi at 20 degrees. And of course, since there's an odd number of quarter wavelengths on each side of the feed, we know it shouldn't be too difficult to match to a typical 50 ohm unbalanced system.
     
    2E0TWG likes this.
  3. AJ6O

    AJ6O Ham Member QRZ Page

    2E0TWG likes this.
  4. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Typical Steve. Elegant, simple, and easier. He will really be missed.
     
    K2CAJ and 2E0TWG like this.
  5. K4EM

    K4EM XML Subscriber QRZ Page

    I just put one up for 40m, strung between my 2 towers. The dimension's are 70' horizontal and 2 35' verticals. I fed it in the corner because it is near 50 ohms and a current point. I used a Wireman 1:1 current bead balun. The SWR low point was at 7.112, a little high so I added 3" to the 2 vertical wires. This made the lowest SWR at 7.080 1.2:1; 1.5:1 at 7.010 and 2:1 at 7.183. All the research I did said feeding it in the bottom was at a VOLTAGE point & several thousand ohms , which required a matching system. It also said there are extreme voltages at the bottom ends of the 2 vertical wires. Feeding at the corner was easy, fast and I had to make just one adjustment. The only thing I don't like is the way I have the balun and coax connection, I think there is room for improvement. The horizontal height is 65 ' and the ends are about 30' off the ground.
    This is still in the testing, config stages but so far seems to work fine on 40m. I put it up to help with the Bouvet operation next week.

    Dave
    k4em
     

    Attached Files:

  6. K4EM

    K4EM XML Subscriber QRZ Page

    I still have to move the coax further away from the vertical wire. It's still a work in progress.
    Dave
    k4em
     
  7. SM0GLD

    SM0GLD Ham Member QRZ Page

    This antenna looks like a OCFD fed at 25%
    A choke must be necessary on antennas like this.
     
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    You obviously didn't read post #2.
     
  9. SM0GLD

    SM0GLD Ham Member QRZ Page

    I did now:)
    I just had to Point out the similarities with the OCFD.
    So many ham's dont like OCFD.
     
  10. KK5JY

    KK5JY Premium Subscriber QRZ Page

    This is likely the challenge, right here -- a good choke that effectively acts like a point-sized break in the outer surface of the coaxial shield. As wavelengths go up, the problem quickly becomes increasingly difficult.

    A choke that is that good for 15m is probably not so hard to build. For 160m?? :eek:
     

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