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Thread: best antenna

  1. #1371
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    I think with the sheer amount of trouble CoCo's are giving us, they are slowly but surely becoming a No-No for us. No matter how careful and diligent we are in making the thing, they just have some "X-factor" that still is a variable to us.
    J-pole and Franklins seems way more reliable, though ever so slightly trickier in making.

  2. #1372
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    Quote Originally Posted by trigger View Post
    Hi abcd and Herman,

    I use the same method as Herman to make the Franklin by folding the wire around a drill bit. My 6 element Franklin is the best (greatest range) antenna I've made.

    Back to CoCo building. I've made 3 x 8 element CoCos in the last few days. 124mm, 116mm, and 109mm as I don't know what the velocity factor of my coax is. The CoCos have been mounted outside on a long piece of dowel appprox 5m above ground.

    Franklin mounted in the loft (3m) gives a range of 250 km
    124mm CoCo gives 125 km
    116mm CoCo gives 100 km
    109mm CoCo gives 100 km

    I had a 3 element 95mm CoCo from previous experiments which gave reasonable results so I added another 5 elements. I gave me 250 km !!

    I've been very careful to check continuity on each of the CoCos as well as gently bending each of the joints with the meter attached to make sure there isn't a dodgy joint.
    You'll have to get these outside, the heavy mineral based materials (tile / slate) used in out roofs would seriously degrade the signals - other areas use lighter materials and they'd getaway with more than we do.

    go to http://www.heywhatsthat.com/ - do a new plot for exactly where you are with your actual antenna height - click 'in the air' (top right of the map and see where 40000 feet ring is. You should reach just beyond that.

  3. #1373
    First officer 1090 MHz's Avatar
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    That looks just like the antenna FlightAware provided. http://ads-b.ca/fa-3.htm
    The problem I had with this antenna was the ground plane radials don't allow the antenna to see too low to the ground so you can't see any ground traffic at the airport. FlightAware doesn't seem to be interested in ground traffic so it's not a problem for them but I like to see all traffic including the ground so I'm using collinear designs.


    Quote Originally Posted by abcd567 View Post
    I also got translation option when I opened the page in Google Chrome, which gave me exactly the same translation as you have written above. What I got from the translation is that:

    (1) The three vertical limbs are (from connector upwards) 136mm, 205mm, and 183mm.
    (2) The circumference of two rings is 69mm (1/4 wavelength), i.e. a rod of 69mm length was bend into a circular shape. The dia of ring is 22mm (69/pi =69/3.1416=22)
    (3) The 4 ground-plane rods (i.e. 4 horizontal rods at connector level) are 69 mm each (1/4 wavelength)
    (4) It was made ​​of yellow welding rods of 1.65 mm diameter.

    I like the construction using welding rods. This makes antenna very sturdy.

    The computer simulation by author of that website gives a Gain = 6.17 dBi, SWR = 1.1

    I have posted above details from that site (http://qsl.net/py4zbz/adsb.htm#b) for forum members who may find it very difficult to understand, as it is not in English.

    I am also posting below some photos from that site for quick reference of forum members.

    Attachment 4489 . Attachment 4485 . Attachment 4486 . Attachment 4487 . Attachment 4488

  4. #1374
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    1090MHZ: That looks indeed rather similar. The so-called "Spiderantenna" has ground plane radials that gets bent slightly downwards, I can only suspect that is done to improve lower altitude coverage?

  5. #1375
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    Quote Originally Posted by 1090 MHz View Post
    That looks just like the antenna FlightAware provided. http://ads-b.ca/fa-3.htm
    The problem I had with this antenna was the ground plane radials don't allow the antenna to see too low to the ground so you can't see any ground traffic at the airport. FlightAware doesn't seem to be interested in ground traffic so it's not a problem for them but I like to see all traffic including the ground so I'm using collinear designs.
    Quote Originally Posted by HermanZA View Post
    1090MHZ: That looks indeed rather similar. The so-called "Spiderantenna" has ground plane radials that gets bent slightly downwards, I can only suspect that is done to improve lower altitude coverage?
    My first reaction to 1090MHz's post was same as HermanZA's reply. I strongly feel bending radials down may improve lower altitude. I will run a simulation for this antenna, one with straight radial & second with bent down radials, and compare the radiation pattern of two to get a conclusive opinion.

    My previous simulations on another antenna has shown that bending down the radials definitely improves Gain & SWR.

  6. #1376
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    Quote Originally Posted by trigger View Post
    Hi abcd and Herman,

    I use the same method as Herman to make the Franklin by folding the wire around a drill bit. My 6 element Franklin is the best (greatest range) antenna I've made.

    Back to CoCo building. I've made 3 x 8 element CoCos in the last few days. 124mm, 116mm, and 109mm as I don't know what the velocity factor of my coax is. The CoCos have been mounted outside on a long piece of dowel appprox 5m above ground.

    Franklin mounted in the loft (3m) gives a range of 250 km
    124mm CoCo gives 125 km
    116mm CoCo gives 100 km
    109mm CoCo gives 100 km

    I had a 3 element 95mm CoCo from previous experiments which gave reasonable results so I added another 5 elements. I gave me 250 km !!

    I've been very careful to check continuity on each of the CoCos as well as gently bending each of the joints with the meter attached to make sure there isn't a dodgy joint.
    Quote Originally Posted by HermanZA View Post
    3mm copper rods.

    (1) What is the diameter of wire you used for your Franklin?
    (2) What is the gap between parallel wires of (a) upper/lower phasing stubs (b) central impedance matching stub of your Franklin?

    HermanZA is using 3mmdia rods with 6mm gap between stub conductors. Computer simulations show that both these figures are too big to get a good impedance match & a descent value of SWR. Gain is not affected by wire diameter or stub conductor gap.
    Last edited by abcd567; 2014-07-28 at 14:13.

  7. #1377
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    Bending the ground plane radials downwards is a cheap trick to alter the feed-point impedance... I doubt very much that the radiation pattern will alter, other than maybe lower the lobes a little towards the ground.

  8. #1378
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    Quote Originally Posted by abcd567 View Post
    (1) What is the diameter of wire you used for your Franklin?
    (2) What is the gap between parallel wires of (a) upper/lower phasing stubs (b) central impedance matching stub of your Franklin?

    HermanZA is using 3mmdia rods with 6mm gap between stub conductors. Computer simulations show that both these figures are too big to get a good impedance match & a descent value of SWR. Gain is not affected by wire diameter or stub conductor gap.
    1) Wire diameter is 1.5mm. It is the Earth wire from UK 13amp ring main.
    2a) Gap between phasing stubs is 3mm 2b) gap of impedance matching stub is 2mm.

    The tap is 25mm from the round (shorted) end of the matching stub.

    I've got a 2m length of 5mm diameter copper tube. What gaps should I be looking for if I use this?
    Last edited by trigger; 2014-07-28 at 20:17. Reason: forgot

  9. #1379
    First officer 1090 MHz's Avatar
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    Quote Originally Posted by Rooster View Post
    Bending the ground plane radials downwards is a cheap trick to alter the feed-point impedance... I doubt very much that the radiation pattern will alter, other than maybe lower the lobes a little towards the ground.
    Yes you are absolutely correct. One might think that simply removing the radials would solve the problem and allow the antenna to see the ground... but doing so will alter the impedance of the antenna and the results would be poor performance if any. The antenna is known as a BS-1105
    http://www.tmrf.co.uk/product/bs-1105/

  10. #1380
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    Quote Originally Posted by trigger View Post
    1) Wire diameter is 1.5mm. It is the Earth wire from UK 13amp ring main.
    2a) Gap between phasing stubs is 3mm 2b) gap of impedance matching stub is 2mm.

    The tap is 25mm from the round (shorted) end of the matching stub.

    I've got a 2m length of 5mm diameter copper tube. What gaps should I be looking for if I use this?
    For STUB wire dia 3mm, and gap between matching stub wires 2mm/phasing stub 1mm, the SWR will be high enough to make antenna unsatisfactory. For 5mm dia wire/tube, it will be worst. Better limit stub wire size 2mm or less.

    VERTCAL LIMB wire dia of 3mm or 5mm does not affect impedance matching/SWR.

    I am using 1mm dia wire (core of RG6) with phasing stub's gap 3mm & impedance matching stub's gap 4mm, which gives me reasoable SWR. Infact ideal gap for matching stub of my antenna works out to be 2.5mm, which is too narrow for adjustable cable tap I am using.
    Last edited by abcd567; 2014-07-28 at 21:51. Reason: Added last paragraph

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