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Thread: best antenna

  1. #1561
    Captain abcd567's Avatar
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    Quote Originally Posted by gregy View Post
    hello ABCD567
    reference your post #1391

    can you pls confirm if this design is for 50 or 75 ohm?
    from the SWR plot it would suggest that its 75ohm

    Q: do the dimensions as shown change for 50 ohm? (im using 50ohm coax cable before/after 50ohm masthead LNA)
    If dimensions are different - is it possible to indicate these?

    thanks
    Yes, the design is based on 75 ohm system, but using it on 50 ohm system will not cause any big loss in performance.

    I did not try how this design matches with 50 ohm. Maybe just moving the cable tap few mm will tune it for 50 ohms system.

    Give me some time to go through the simulation /modelling to workout the 50 ohms dimensions, if different.

  2. #1562
    Captain abcd567's Avatar
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    Quote Originally Posted by YWYY View Post
    Yes thanks for giving me that file. Its very useful, I am learning to use it - slowly. I figured that to use FAR FIELD. When I run it I get errors found - run segment check. It still works ok , but maybe my settings are different to yours.
    Mike
    It always give me "errors found-run segments check", but the results are ok so i simply ignore it. I use default settings & free space.

  3. #1563
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    Quote Originally Posted by gregy View Post
    hello ABCD567
    reference your post #1391

    can you pls confirm if this design is for 50 or 75 ohm?
    from the SWR plot it would suggest that its 75ohm

    Q: do the dimensions as shown change for 50 ohm? (im using 50ohm coax cable before/after 50ohm masthead LNA)
    If dimensions are different - is it possible to indicate these?

    thanks
    Quote Originally Posted by abcd567 View Post
    Yes, the design is based on 75 ohm system, but using it on 50 ohm system will not cause any big loss in performance.

    I did not try how this design matches with 50 ohm. Maybe just moving the cable tap few mm will tune it for 50 ohms system.

    Give me some time to go through the simulation /modelling to workout the 50 ohms dimensions, if different.
    I have done simulation for 50 ohm.
    The Gain & Cable Tap position are same as for 75 ohm.
    SWR is a little bit higher i,e for 75 ohm it was 1.52, and for 50 ohm it is 2.08.

    SWR can be reduced if the Matching stub gap is reduced, but it is difficult to achieve narrower gaps and sharper bends with a thick wire of 3mm dia.

    Please see the simulation Results for 50 Ohm system:

    franklin-50 ohm-4E-3mm wire-6mm gap-round bend-gain-pattern.png
    Last edited by abcd567; 2014-08-31 at 03:19.

  4. #1564
    Captain abcd567's Avatar
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    NEW ANTENNA - THE COILED DIPOLE


    STEP 1 - MODELLING & SIMULATION




    STEP 2 - CONSTRUCTION




    STEP 3 - TRIAL RUN
    The the Camera Flash has created shadows of coils on the blinds, making coils look like double helix, with much more than actual number of turns.
    Last edited by abcd567; 2014-09-02 at 17:09.

  5. #1565
    Captain abcd567's Avatar
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    .
    The VRS Coverage of the Coiled Dipole (see above post).

    12 hrs trial run Without Amplifier. Length of Coax Cable between antenna & receiver = 12 ft (3.5 meters).

    Range rings are 50 nautical miles apart



    Last edited by abcd567; 2014-09-02 at 21:58.

  6. #1566
    Captain abcd567's Avatar
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    ANOTHER EXPERIMENT - CANTENNA WITH COILED WHIP

    image 1 of 2 - Photo




    image 2 of 2 - Coverage 12 hrs run
    Without Amplifier, 12 ft/3.5 meter coax cable between antenna & receiver

    Range Rings are 50 nautical miles apart.


  7. #1567
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    and now the amplified coiled dipole?

  8. #1568
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    Quote Originally Posted by peterhr View Post
    and now the amplified coiled dipole?
    Ok, will do trial run this weekend: coiled dipole+ Amplifier +50 ft/15m rg6 coax between antenna & receiver..

    Have done trimming of 1/2 wavelength dipole.

    The dipole limbs were trimmed in steps of 3mm, then put to trial run after each trim. Started from 69mm, went upto 60mm. As the length was reduced, range reduced, the number of far away planes reduced, and number of nearby planes increased.
    Last edited by abcd567; 2014-09-03 at 20:33.

  9. #1569
    Captain abcd567's Avatar
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    Can anyone guide me which is an INEXPENSIVE equipment to measure SWR/reflected power/impedance of an antenna or transmission line? Any idea about cost of such equipment? I have a very limited budget for my hobby.

  10. #1570

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