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Thread: best antenna

  1. #1781
    Captain abcd567's Avatar
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    No input from forum members on CoCo impedance Matching/Tuning equipment/techniques???
    Many forum members are Amateur Radio Operators, some are long-timers as well, and sure have good experience on this issue. their input can be very valuable.

  2. #1782
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    In DIY environment, CoCos are rarely made accurate enough to give good performance.
    Although inaccuracies affect Gain & SWR both, but the Gain is relatively less affected by errors than the SWR, which changes profoundly with changes in length of element.

    What I am aiming at is a "Magic Box" which can be inserted at antenna feed point, and which should be capable of compensating the affect of these inaccuracies.

    My objective is to find an impedance matching / SWR reduction method which can achieve this by simply turning one or two knobs/adjustments and without use of any equipment such as Network Analyser (VNA) or SWR Meter etc.

    Any ideas / sugesstions?

  3. #1783
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    Simulation results for CoCo made of RG6 Coax (FPE insulation, 0.83 VF, element length=114mm, half-element length=57mm)
    Proves CoCo is a high impedance high SWR antenna.
    Adding a shorted 1/2 element & a whip could not bring SWR below 3

    1. 8-Element SWR = 3.4 Gain = 8.55 dBi
    2. 8.5-Element, Shorted Top SWR = 2.92 Gain = 8.93 dBi
    3. 8.5-Element, Shorted Top+Whip SWR = 3.57 Gain = 8.85 dBi

    8-element
    Gain-Pattern Swr-CoCo 8 Element RG6 FPE VF 0.83.PNG

    8.5-element shorted top
    Gain-Pattern Swr-CoCo 8.5 Element Shorted Top RG6 FPE VF 0.83.PNG

    8.5-element shorted top + whip
    Gain-Pattern Swr-CoCo 8.5 Element Shorted Top + Whip RG6 FPE VF 0.83.PNG

  4. #1784
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    Quote Originally Posted by abcd567 View Post
    No input from forum members on CoCo impedance Matching/Tuning equipment/techniques???
    Many forum members are Amateur Radio Operators, some are long-timers as well, and sure have good experience on this issue. their input can be very valuable.
    I said this before, and Ill say it again...

    You are using a VERY large hammer to crack the nut !
    I'd bet that if you took a straw poll, 99% of the forum users couldn't care less about the "rocket science"... they only want to knock up a working antenna.
    Matching feeder to antenna at these frequencies requires an accuracy few could attain, so is basically a waste of effort - without the correct test equipment totally pointless.

    When I first got my TV dongle, I made a coco out of spare satellite cable... no idea of specs whatsoever ! 11cm a section.... fed with an old tv coax feed into the shack (again, zero maths)

    Compared to a commercially built active scanner antenna (same feeder) the coco provides more than 10dB gain over the scanner antenna.

    So YES you can lash up a good antenna with nothing more than a tape measure.

  5. #1785
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    This is exactly why - for newbies - I suggest making up a dipole and to tie it to a gallows made of bamboo cane.

    The cost is just some old coax (they might have in the shed), some cane (from the garden)

    Fix it to the spouting / guttering at the roof edge so it's as high up as possible and vertical

    The only things to be careful of are not a long down lead (5m or so is ok), and getting decent connectors to adapt the coax to the MCX input on the dongle.

    This will give up to 200nm / 350km range

    Then think about something better.

    For people in high rises there are special considerations...

    They will get the benefit from the height, but are disadvantaged by having to work behind glass (with whatever coatings it has to reflect various wavelengths for heat retention) and a restricted view (unless they can see out of all sides of the building)

  6. #1786
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    Quote Originally Posted by Rooster View Post
    I said this before, and Ill say it again...

    You are using a VERY large hammer to crack the nut !
    I'd bet that if you took a straw poll, 99% of the forum users couldn't care less about the "rocket science"... they only want to knock up a working antenna.
    Matching feeder to antenna at these frequencies requires an accuracy few could attain, so is basically a waste of effort - without the correct test equipment totally pointless.

    When I first got my TV dongle, I made a coco out of spare satellite cable... no idea of specs whatsoever ! 11cm a section.... fed with an old tv coax feed into the shack (again, zero maths)

    Compared to a commercially built active scanner antenna (same feeder) the coco provides more than 10dB gain over the scanner antenna.

    So YES you can lash up a good antenna with nothing more than a tape measure.
    But there is the challenge of getting something to work better. Pushing the boundaries. It's what humans are made for.

  7. #1787
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    Quote Originally Posted by Rooster View Post
    I said this before, and Ill say it again...

    You are using a VERY large hammer to crack the nut !
    I'd bet that if you took a straw poll, 99% of the forum users couldn't care less about the "rocket science"... they only want to knock up a working antenna.
    Matching feeder to antenna at these frequencies requires an accuracy few could attain, so is basically a waste of effort - without the correct test equipment totally pointless.

    When I first got my TV dongle, I made a coco out of spare satellite cable... no idea of specs whatsoever ! 11cm a section.... fed with an old tv coax feed into the shack (again, zero maths)

    Compared to a commercially built active scanner antenna (same feeder) the coco provides more than 10dB gain over the scanner antenna.

    So YES you can lash up a good antenna with nothing more than a tape measure.
    Quote Originally Posted by peterhr View Post
    This is exactly why - for newbies - I suggest making up a dipole and to tie it to a gallows made of bamboo cane.

    The cost is just some old coax (they might have in the shed), some cane (from the garden)

    Fix it to the spouting / guttering at the roof edge so it's as high up as possible and vertical

    The only things to be careful of are not a long down lead (5m or so is ok), and getting decent connectors to adapt the coax to the MCX input on the dongle.

    This will give up to 200nm / 350km range

    Then think about something better.

    For people in high rises there are special considerations...

    They will get the benefit from the height, but are disadvantaged by having to work behind glass (with whatever coatings it has to reflect various wavelengths for heat retention) and a restricted view (unless they can see out of all sides of the building)
    Quote Originally Posted by trigger View Post
    But there is the challenge of getting something to work better. Pushing the boundaries. It's what humans are made for.
    Yes, very true.. meeting the challenge..getting something work better.

    The topic of this thread is not "a working antenna" or "an easy DIY antenna" or "a good antenna'. It is "BEST ANTENNA"... a never ending topic with continous effort to improve .... like from walking to horse riding to railways to cars to airplanes to space craft... meeting the challenge....never ending quest for the best...that is what makes humans superior to all living things on this planet.

  8. #1788
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    Thanks Rooster, peterhr, and trigger for your opinions.
    Yes, we have to strike a balance.

    We should look for the "best" but prime objective should be to keep making the antenna for novice "easy & practical".
    What I am struggling to find a way to tame the wild CoCo (most novice got poor results, few lucky ones moderate to good results). This can only be done if we are able to analyze and understand it, and then try various ways to tame it.

  9. #1789
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    Quote Originally Posted by Rooster View Post
    ........I'd bet that if you took a straw poll, 99% of the forum users couldn't care less about the "rocket science"... they only want to knock up a working antenna.......
    I fully agree to the part of your reply quoted above. That is why I have posted 1/2 wavelength dipole (my very fitst post in this forum) & the Cantenna without mentioning any maths or theory, though I myself had to go through it before I made those antennas.

    .....So YES you can lash up a good antenna with nothing more than a tape measure....
    The failure of most novice to get good results from collinears like CoCo & Frankline contradicts your statement quoted above.

    The reason for tricky nature of collinears stems from:

    (1) Their performance is profoundly sensetive to dimensions due to phasing involved.

    (1) These have high complex impedance (several hundred ohms, resistive+reactive) compared to the Coaxial feeder & receiver (75 or 50 ohms, predominantly resistive).

    Above two characterstics require impedance matching techniques to be incorporated (either as part of the antenna or a separate matching unit) to get a good performance. This results in "maths" & "rocket-science" to jump-in. This makes "lashing up a good antenna with nothing more than a tape measure" very difficult and a matter of chance only.

    With all above difficulties, I still want to come up with good antenna designs which:

    (1) can be lashed up with nothing more than a tape measure.

    (2) uses the most commonly and readily available, low cost materials to make it.

    1/2 wavelength dipole & cantenna are examples of this approach.

    Although at this stage of taming the CoCo, I am involved in theory & maths, and exploring all options including difficult ones, once I find a solution, I will post it in a simple way without rocket science : ) as I have done it for Cantenna & Dipole.

  10. #1790
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    We are strugling with 1 Ghz wireless antenna, while others have started using 60 Ghz wireless.

    Click here: 60 GHz WiFi

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