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

    Z for that particular antenna here.

    [​IMG]
     
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  2. KF6A

    KF6A Ham Member QRZ Page

    That's why I stated it was generated from the VE3SQB quagi generator so anyone can produce one for themselves. But for sake of brevity here is the requested info.

    [​IMG]
     
  3. KF6A

    KF6A Ham Member QRZ Page

    The problem with modeling the quagi using the N6NB dimensions is that the reflector and driven element use "TW wire" which is insulated. I can guess the exact thickness of the insulation, and I can assume from spec sheets that they used PVC as an insulating material, but guessing doesn't usually result in the most accurate results. But if I take my best WAG at it the model looks something like this for the N6NB version with the reflector and driven element lengths compensated for no insulation.

    Now granted the quagi pattern looks pretty darn good for manually changing element spacings and lengths way back in the day. But modern computer optimized yagis are, IMHO, the better way to go. Not knocking the quagi, but better mousetraps are available.

    [​IMG]
     
  4. W0BTU

    W0BTU Ham Member QRZ Page

    Thanks! That statement about the VE3SQB quagi generator went over my head. I never heard of it until now.

    As for that TW wire insulation, can a model take that into consideration? Even if we knew the dielectric constant and thickness of the insulation, part of the field is in that and part of it is in the air.

    I think that if I ever get back on 2m SSB/CW, I'll likely use Yagis. I appreciate your advice.
     
  5. KF6A

    KF6A Ham Member QRZ Page

    You can model insulated wires with EZNEC. Looks like this.

    [​IMG]

    That's the additional wire I added for the reflector and driven element loops to compensate for not being insulated, from the insulated measurements.

    Another "limitation" is that EZNEC (not sure about EZNEC 6) can only model a single type of material at a time. So the model has to be all copper, or all aluminum. I think 4nec2 allows one to use different materials on different wires, but I'm not sure. I do know that "Antenna Model" does allow you to specify a different material for each wire.
     
    Last edited: Nov 4, 2016
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  6. KF6A

    KF6A Ham Member QRZ Page

    This is my BWAG at the insulation thickness and material.

    [​IMG]

    So now using the published lengths and spacings the N6NB quagi plot looks something like this.

    [​IMG]

    But the model is still all aluminum or all copper in EZNEC. I'll try running it in Antenna Model and see what that comes up with. That didn't work. It allows different materials but not insulation, LOL. Was worth a shot.
     
    Last edited: Nov 4, 2016
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  7. KF6A

    KF6A Ham Member QRZ Page

    Looks like 4nec2 can model different materials and insulation. If anyone wants to tackle that one please feel free.
     
  8. AI3V

    AI3V Ham Member QRZ Page

    Impressive!

    Equal gain
    Better g/t
    Direct feed
    Easier to build

    What's not to like?

    Looks like the quagi is dead!

    Long live the KF6A notAquagi. :)

    Rege
     
    W0BTU likes this.
  9. N4OGW

    N4OGW Ham Member QRZ Page

    When I modeled the quagi with N6NB's dimensions I simply multiplied the driven and reflector loops by the same constant factor to correct for the wire insulation. Then I adjusted that factor to minimize the SWR (which can be done automatically in 4nec2). The pattern I got looked similar to KF6A's.

    Tor
    N4OGW
     
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  10. N4OGW

    N4OGW Ham Member QRZ Page

    That may have been true 30 years ago. Let's see:

    Quagi:

    1. Cut elements and boom to length
    2. Put elements on boom. Adjust driven loop length slightly to peak SWR.

    50 ohm yagi:

    1. Cut elements and boom to length
    2. Put elements on boom. Adjust driven element length slightly to peak SWR.

    Which is "cookbook"? :)

    Tor
    N4OGW
     

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