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Thread: best antenna

  1. #771
    Captain abcd567's Avatar
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    ANOTHER EXPERIMENTAL DESIGN - 5/8 WAVELENGTH DIPOLE WITH TUNING/IMPEDANCE MATCHING COIL.
    FITS INSIDE 25mm PVC PIPE

    NOT BUILT & TESTED YET

    REVISED ON APRIL 03, 2014 DUE TO ERROR IN EARLIER INPUT/OUTPUT DATA

    Gain = 5.81 dBi, SWR = 1.37

    SEE BELOW SCREENSHOTS OF COMPUTER SIMULATION USING 4NEC2 SOFTWARE
    (available free of cost at http://www.qsl.net/4nec2/):


    SIMULATION OUTPUT: ANTENNA LAYOUT, SWR, GAIN, & PATTERN
    dipole+coil-output-R1.png

    INPUT: DIMENSIONAL DATA OF ANTENNA, FREQUENCY, CABLE IMPEDANCE, CABLE CONNECTION POINT
    dipole+coil-input-R1.jpg

    COIL & FEED DETAILS
    dipole-coil-details-R1.png
    Last edited by abcd567; 2014-04-03 at 16:35.

  2. #772
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    i managed to have a quick play at lunchtime with sprectrum analyser today, i thibk after getting my coupler the right way round i got some readings, the quick and dirty bent bit of wire wedged in a tnc connector did have a resonance near 1090MHz 3 db's or so but the good resonance was down at 860MHz 12 db's.

    Tried to use the network analyser but was got confused by its calibration procedure and ran out of time, once i'm happy and i sort of know what i'm doing i'll get some screen grabs of stuff.
    T-EGLF8

  3. #773
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    Quote Originally Posted by SpaxmoidJAm View Post
    i managed to have a quick play at lunchtime with sprectrum analyser today, i thibk after getting my coupler the right way round i got some readings, the quick and dirty bent bit of wire wedged in a tnc connector did have a resonance near 1090MHz 3 db's or so but the good resonance was down at 860MHz 12 db's.

    Tried to use the network analyser but was got confused by its calibration procedure and ran out of time, once i'm happy and i sort of know what i'm doing i'll get some screen grabs of stuff.
    Good! Keep it up. We all will benefit from your work

    Sent from my N762 using Tapatalk 2

  4. #774
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    please post how to make a resonator coil; turns, diameter etc

  5. #775
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    Quote Originally Posted by charan View Post
    please post how to make a resonator coil; turns, diameter etc
    Did you not click the images? they are there.

    Length required to make turns can be made with antenna 5/8 calculators. Which at 1090mhz is 160mm

    If they are 1/4 wave coils. The standard length is 56mm

  6. #776
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    I worked out where i was going wrong with the network analyzer and made a quick aerial this lunchtime, in fact i made the top half of this aerial with four 138mm radial arms for the ground plane


    Attachment 3760
    This was the output
    test2.jpg

    although the notch at 1090MHz isnt as big as the one around 860 its got reasonable bandwidth.
    Last edited by SpaxmoidJAm; 2014-04-04 at 15:13.
    T-EGLF8

  7. #777
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    Quote Originally Posted by SpaxmoidJAm View Post
    I worked out where i was going wrong with the network analyzer and made a quick aerial this lunchtime, in fact i made the top half of this aerial with four 138mm radial arms for the ground plane


    Attachment 3760
    This was the output
    test2.jpg

    although the notch at 1090MHz isnt as big as the one around 860 its got reasonable bandwidth.
    Try to trim the limb lengths slightly. This may improve 1090 MHz notch.

  8. #778
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    Quote Originally Posted by SpaxmoidJAm View Post
    I worked out where i was going wrong with the network analyzer and made a quick aerial this lunchtime, in fact i made the top half of this aerial with four 138mm radial arms for the ground plane


    Attachment 3760
    This was the output
    test2.jpg

    although the notch at 1090MHz isnt as big as the one around 860 its got reasonable bandwidth.
    Try also (1) bend downwards the earth plane wires, so that their tips are say about 40 to 50 mm below horizontal (2) use a little longer earth plae wires say 150 mm instead of 138mm

    Sent from my N762 using Tapatalk 2

  9. #779
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    VELOCITY FACTOR OF COAXIAL CABLES:

    The velocity factor VF of a medium is ratio of velocities of propagation of Electromagnetic waves in that medium (v) and in vacuum (c).

    The velocity of propagation of Electromagnetic waves in a medium depends on:
    (1) Medium's electrical characteristic relative permittivity er.png (dielectric constant)
    (2) Medium's magnetic characteristic relative permeability ur.png (which is the measure of the ability of a material to support the formation of a magnetic field within itself).

    VF4a.png

    Velocity Factor
    VF4b.png

    Values of Relative permeability ur.png
    Relative permeability is usually 1 for non-magnetic materials such as cable insulation materials.

    Values of Relative permittivity er.png
    • Vacuum = 1 (by definition)
    • Air = 1.00058986
    • PTFE/Teflon = 2.1
    • Polyethylene = 2.25
    • Foamed Polyethylene = 1.75 to 1.35
      (foamed polyethylene is a mixture of gas and polyethylene and it's electrical parameters depend on solid to gas proportion)

    Hence Velocity Factors (VF) are calculated as follows:
    • For PTFE/Teflon insulated coax, VF = 1 / √(2.1 x 1) = 0.69
    • For Polyethylene insulated coax, VF = 1 / √(2.25 x 1) = 0.66
    • For foamed polyethylene insulated coax, the VF ranges between VF = 1 / √(1.75 x 1) = 0.76 & VF = 1 / √(1.35 x 1) = 0.85



    **Information below is quoted from Coaxial Cable Manufacturer Belden's Catalouge:
    DIELECTRIC CONSTANT
    • Symbol: er.png
    • Very important for electronic cables
    • Lower er.png = Lower capacitance, Higher impedance, Lower attenuation.
    • Air is best dielectric (er.png = 1)
    • Adding air to (foaming) any material lowers its dielectric constant er.png.


    .
    Last edited by abcd567; 2014-04-06 at 23:04.

  10. #780
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    Quote Originally Posted by abcd567 View Post
    Try also (1) bend downwards the earth plane wires, so that their tips are say about 40 to 50 mm below horizontal (2) use a little longer earth plae wires say 150 mm instead of 138mm

    Sent from my N762 using Tapatalk 2
    That has improved the notch, but I think the inherent problem with this design is that you cannot adjust the other two lengths of the antenna. Making it not the best design to go for if your making your first antenna. That being said 5.5 to 6 db's isn't to bad.

    test3.jpg

    what I might try is coupling each stage with a connector so it can be adjusted but again anyone without equipment would be working blind.

    Think a collinear is next to try.

    here's the aerial
    WP_20140404_001.jpg
    Last edited by SpaxmoidJAm; 2014-04-07 at 07:05.
    T-EGLF8

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