Quagi antenna

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KA0EIV, Nov 2, 2016.

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  1. KF6A

    KF6A Ham Member QRZ Page

    If G/T is what one considers the standard of FoM for a 2m yagi then this particular model looks like this compared to others.

    I wouldn't be so bold as to proclaim the quagi is dead, but as I stated in a previous post there are better mousetraps available today.

    [​IMG]
     
    Last edited: Nov 4, 2016
  2. KF6A

    KF6A Ham Member QRZ Page

    Or if ones standard for FoM is something other than G/T, like this FoM chart.

    [​IMG]
     
    Last edited: Nov 4, 2016
  3. AI3V

    AI3V Ham Member QRZ Page

    Looks like a really nice diy antenna for satellite work.

    I just realized that the dipole driven element is a improvement over the loop in one other area which is really important in "keeping an antenna up".

    The antenna is open circuit to DC.

    When water does work its way into the feedpoint connections it causes a relatively high resistance that kills your signal, with a open circuit antenna you can easily measure with a ohmmeter (or better a high voltage "megger") and test for water leakage.

    You can always put a DC shunt at the rig end if you prefer for static.

    Rege
     
  4. W0BTU

    W0BTU Ham Member QRZ Page

    I thought 43 material was for 75m thru 20m or so. How did that work?
     
  5. N4OGW

    N4OGW Ham Member QRZ Page

    Fair-Rite has type 43 listed as "25-300 MHz". Maybe they have another material that would be slightly better, but that is what I had on hand.

    http://www.fair-rite.com/43-material-data-sheet/

    Tor
    N4OGW
     
  6. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Nobody was asking for a better mousetrap. Nobody has ever claimed the Quagi was a top performing design.

    What the Quagi has is something that will never go out of popularity:
    -Hardware store parts
    -Minimal cost
    -Easy to build
    -No special tools required
    -Wide bandwidth
    -No fiddly matching required
    -Short and long boom models for multiple bands
    -Construction and materials that can be bashed around a bit
    -Reliable design

    There is no doubt that the element spacings can be better optimized with modern modeling software; but that will just improve an old favorite.

    If you need Ferrari performance then buy or build a Ferrari design. This is just an simple reliable with good performance that works.
     
    W0BTU likes this.
  7. N4OGW

    N4OGW Ham Member QRZ Page

    No need for feigned drama QAA.

    The original type of wire used (TW) isn't available anymore. What is available, THHN, has a slightly different vf, so trimming the DE (and reflector) is usually needed. Here it is from the horse's mouth, http://n6nb.com/quagi.htm

    "In the original design, covered solid #12 TW house wire was used for the quad-style elements. The use of other types of wire, or even removing the insulation, may change the resonant frequency enough that the length has to be adjusted. Suggestion: build the antenna to the dimensions shown in the chart and run an SWR curve, noting the SWR above and below the desired operating frequency. If it is lowest below the desired frequency, the driven element should be made shorter--or longer if the SWR is lowest above the desired frequency. The reflector should then be adjusted in length a similar amount. Many builders have used THHN wire, which is more readily available than type TW now. They generally report that the resonant frequency is higher than expected, which means the loop elements have to be lengthened slightly for THHN wire. Tests in 2003 indicated that each wire loop should be about one percent longer than the original dimension if THHN wire is used. "

    When I built mine, I ended up modelling it and building it with bare wire for the loops.

    Tor
    N4OGW
     
    KF6A likes this.
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    OGW:

    If you follow the directions, and lengthen the wire by 1% for the wire difference, then you are again at the "cookbook" measurements!

    As I have said, and others have said, there are no claims that the quagi is an optimum design! It IS a good "workhorse" design, NOT a "racehorse" design. There is definitely a difference.

    Glen, K9STH
     
  9. KF6A

    KF6A Ham Member QRZ Page

    Your proposition is absurd as that's exactly what the premise of this thread was originally about. I submit the evidence below.

    That sounds like someone seeking a "better mousetrap" to me. If you don't come away with the same conclusion after reading that then you're reading into something that doesn't exist or you simply wish to be contrary. You are welcome to be contrary and read into things that don't exist, but you are not welcome to your own facts.


    There is nothing on a standard 50ohm yagi, like the specific example that I used, which requires parts one cannot get at a store where one can also buy parts to build a quagi. You're welcome to disagree but you would be incorrect. In fact the example I posted originally started life as a 70cm yagi I had previously designed and built for seeking power line noise. The design worked so well I decided to scale it to 2m and the example I posted in this thread is the result of that. When I built that version of the yagi I used thin walled PVC tubing for the boom so it would be light weight and hand held for seeking power line noise with a hand held 70cm radio (I used a hand held scanner tuned to 70cm and using AM). The driven element used a small piece of fiberglass rod I got from the same hardware store to separate the two sides of the driven element, and the ring terminals I used to feed it from coax can be purchased at walmart or any other regular run of the mill hardware store. Whatever you can use to build a quagi can also be used to build a yagi. Either you haven't built very many yagis or you're simply trying to be contrary? It matters not which as you'd still be wrong.
     
    Last edited: Nov 5, 2016
  10. KF6A

    KF6A Ham Member QRZ Page

    To the OP, good luck with whatever path you choose. I have nothing more to add. I shall return to what I was doing before I decided to give assistance in this thread and finish up another 2m array I am designing for a friend as it would seem that would be a more productive use of my time.
     
    Last edited: Nov 5, 2016

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