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23-cm BiQuad Antenna with Lips

Discussion in 'Amateur Radio Antennas' started by C2, Apr 2, 2011.

  1. C2

    C2 Well-Known Member

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    I had been inspired to try ATV (amateur TV) on 23-cm and built this antenna to feed an old 10-foot C-band satellite dish I had.



    The design is based on plans for a WiFi biquad that I found on the Internet:

    Biquad Antenna Construction

    I scaled these dimensions for my frequency and made adjustments along the way.

    I first bent a length of 12-guage solid copper wire (common house wire), a total of 19.5 inches, into a shape to make two squares with the ends at the center of the long dimension.

    Then I made a reflection plane with an additional 1/2-inch on each side to help the directivity (the lips).

    I fed the antenna with some semi-ridged scrap coax and adjusted the offset from the reflection plane for lowest SWR (about 1/4-wave away).

    [​IMG]

    I’ve added an SMA connector to fit with my 23-cm ATV station.

    Below is an SWR plot I made with an antenna analyzer. The SWR shown is a bit off as the station it is used with is a 75-ohm station and the analyzer is 50-ohm. It works well nonetheless.

    [​IMG]

    I also made gain measurements comparing to a reference dipole antenna from a distance of 30 feet and measured a 9.9 dBd gain at operating frequency. This comparison worked well given the flat dipole's nominal impedance of 72-ohms.

    I’ve been most pleased with this design and have even made a DTV antenna that works just as well as commercial antennas. I would suggest one for directed 70-cm operations over many of the popular yagi style antennas, as I believe they have a better F/B ratio.
     
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    Last edited: Apr 2, 2011
  2. Robb

    Robb Yup

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    Niiiiiiice!
     
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  3. Moleculo

    Moleculo Administrator Staff Member

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    C2,

    Would you mind going into some more detail on your ATV station and what type of activities you're doing with it? In all honesty, I understand the principles of ATV, but I've never really talked to anyone about the details of how to do ATV and why I would want to try it. Are there a lot of stations in your area doing it?

    Also, how are you making that main element stand off from the reflector? I can't quite figure it out from the pic.
     
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  4. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Nice work.

    I built a double biquad and use it for 1900MHZ reception on wireless ISP.

    I used solid metal for the reflector and put it on an old hughes net parabolic dish.

    Hard to beat those biquad at such high frequency with a parabolic reflector.
     
    #4
  5. C2

    C2 Well-Known Member

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    The main element is soldered to semi-rigid coax. The outer shield is usually tin or copper, and I just soldered the coax to the screen. It is not super strong, but strong enough for what I was doing. I will add some standoffs at the tips to secure the element better.

    ATV was more experimenting than regular use. I have a 23-cm station from low power modules that I bought off ebay from a Norwegian fellow. Similar to the ones here:

    ATV Special Offers, Pakage Deals and Offers Amateur Televsion

    Just plug in your monitor, cam, and mic and you can run a full duplex station. My stuff is boxed up now, but I was just using my TV and point-n-shoot cam.

    My area has K6BEN, a 23-cm repeater station that downlinks to one of the 70-cm ATV stations, and it can be received on a regular CATV with just rabbit ears. He runs a net every Wed. night and is crosslinked on several repeaters in 70-cm, 1.25- and 2-meters.

    The Silicon Valley ATV Group

    I tried to hit his repeater, but I think there is a building in the way...
     
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