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Thread: best antenna

  1. #1661
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    thanks for both your responses im motivated to give the franklin (another) try
    and this time be DIY pedantic in construction.
    either way i want something to benchmark the coco against, im obsesive to determine if i have yet maxxed
    out my range ... given physical constraints of my antenna height and terrain.

    a couple of questions for you both
    1) wire available to me are
    brass rod dia 2.6mm
    copper wire dia 1.6mm
    (have tried but cant get 2mm copper)
    id prefer using the brass - given its greater mechanical benefit for supporting antenna shape etc
    i note you have given dimensions for "2mm wire" and that phasing and matching stub dimensions are quite critical.
    Q; which to use? and how should i adjust the gap accordingly?
    2) i believe your dimensions are for 75ohm,
    Q; what dimensions of antenna would change for optimising to 50ohm?
    if its only the feeder connection on stub - then no problem - i have a VNA and hence can adjust position on matchung stub to minimise VSWR)
    (im using LNA and feeder both 50ohm... hence wish to also ensure minimal mismatch at antenna to 50ohm,
    and leave the mismatch loss to occur at 75ohm power injector/ SDR at bottom of feeder - after LNA gain where impact
    should be minimal)

    i appreciate your encouragement and help... and in due course will post my VNA test/tuning experience with franklin,
    and also range plots of coco (4.5) vs franklin

  2. #1662
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    Quote Originally Posted by gregy View Post
    thanks for both your responses im motivated to give the franklin (another) try............a couple of questions for you both..............
    I will re-model the franklin for both of your wire sizes of 1.6mm & 2.6mm dia (2 models) with 50 ohm impedance match, and run the simulation to optimize dimensions, then post the results. I plan to do it this weekend.
    Last edited by abcd567; 2014-09-24 at 04:36.

  3. #1663
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    brilliant! and very much appreciated.

  4. #1664
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    Hi gregy
    How sharp can you bend 2.6mm dia brass rod? I mean if you bend a piece of brass wire in the shape of letter U, how much mimimum gap you can achieve without cracking or kinking the wire at the bend?

  5. #1665
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    good question, will try tonight when home from office, (opp time zone to you)
    i have gas torch for heating - so presumably can also heat a little to reduce tendency to tear the brass on tight bend.
    ... will post outcome of some differnet radius U bends.. i will try for an internal gap of 3mm.. but this may be ambitious.
    (would give distance of 5.6mm between centre of brass dia 2.6 wire .. eg 3+1.3+1.3 )
    aka will try 3/3.5/4mm drills as a mandrel for U bends

  6. #1666
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    Neat U-Bend & L-Bends (and a neat soldering job)

    Last edited by abcd567; 2014-09-24 at 06:51.

  7. #1667
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    I received the price of this antenna:

    http://www.taiwan-antenna.com/front/...tenna-N-Female

    It costs 78 usd + shipping + taxes

    Honestly I do not think good price

  8. #1668
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    Quote Originally Posted by trigger View Post
    Hi gregy,
    I have made a few Franklins and found them to be superior to any of the CoCos I've made. I first made this one. I then made another but added an extra couple of vertical segments and stubs. The diameter of the wire I used was 1.5mm. As with any antenna, accuracy is king.

    Later models used the spec as in this post http://forum.flightradar24.com/threa...ll=1#post56957 with the slightly longer matching stub.
    Which design/model gave you the best results?

  9. #1669
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    hi abc567
    dug out the caliper for accuracy
    brass rod diamater = 2.5mm
    gap between brass rod = 5.0mm

    i tried smaller gap - however the radius of bend is to severe and brass fractures
    5mm appears to be reproducable and reliable from fracture of brass

    if you could model with 2.5mm brass and 5mm gap between phasing and matching stubs
    and for 50ohm

    much appreciated thx
    Last edited by gregy; 2014-09-24 at 16:11.

  10. #1670
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    Quote Originally Posted by gregy View Post
    hi abc567
    dug out the caliper for accuracy
    brass rod diamater = 2.5mm
    gap between brass rod = 5.0mm

    i tried smaller gap - however the radius of bend is to severe and brass fractures
    5mm appears to be reproducable and reliable from fracture of brass

    if you could model with 2.5mm brass and 5mm gap between phasing and matching stubs
    and for 50ohm

    much appreciated thx
    Is 5mm the gap between surfaces of stub wires or is it center-to-center distance between stub wires? I mean "did you use 5mm drill bit as a mandrel for U bends?"
    Last edited by abcd567; 2014-09-24 at 19:16.

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