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Optimize the Whip Antenna Which Is Supplied With DVB-T Dongle

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  • abcd567
    replied
    Originally posted by thehague View Post
    Did you already try this?
    Yes, did try. There is not any noticeable difference between placing on metallic can with plastic cover, and without plastic cover

    Further reading on whip antenna optimization:

    Trial Run Results for Three Types of Whip Antennas

    .
    Last edited by abcd567; 2017-08-29, 22:04.

    Leave a comment:


  • thehague
    replied
    Originally posted by abcd567 View Post
    FURTHER IMPROVEMENT
    Things to be tried:
    1. Remove black plastic circular adhessive cover from bottom of antenna, and check electrical continuity between exposed metal base plate & the outer metallic part of MCX connector at other end of antenna's coax.

    2. Place exposed base on a metallic can and check if direct contact gives any improvement.
    Did you already try this?

    Leave a comment:


  • abcd567
    replied
    Originally posted by rueckwaertsflieger View Post
    1 In case you are willing to increase your targeted antenna segment length 10 fold, you might have a chance. The length of both the active elments should be less than 69mm.
    2 The design you are targeting probably is just one kind of a sleeve antenna. Turning back the cable screen around the feeding coax with coating after stripping the cable coating for a magnitude of less than 65mm - around 45? depending on cable type - and using around 65mm inner conductor as whip. Theoretically you might get rather good results with this antenna. In practice the characteristics are defintitely sensitive to tiny changes in geometry. Further, you have to optimize length of shield folded back and whip experimentally. The screen has to be shorter than wavelentgh in free air by a factor near the velocity factor of the cable and so on.
    3 In case you will try this design, use very thick cable and a rigid sleeve. This will somehow make your design more robust. Probably you could choose Ecoflex 15 plus copper tubing 15mm for the sleeve, connected to the shielding.
    4 In case, you won't have success, go back to the cantenna design, turning out to be a somewhat sleeved antenna with dimensions such big, gaining much more robustness against mechanical variation.

    However, a not optimized sleeve antenna definitely will outperform the funny whip antenna provided with the electronics as long as you go close to half wavelength with both the active elements - in other words: do not try 6.5mm but less than 69.

    Good luck
    The statement "The screen has to be shorter than wavelentgh in free air by a factor near the velocity factor of the cable" is a misconception.

    The coaxial cable's Velocity Factor is applicable to the circuit formed by inner surface of shield and core wire of coax with PE or FPE etc insulation completely filling the gap between core and shield.

    In case of sleeve, the circuit condutors involved are the sleeve's inner surface and shield's outer surface. The insulation between these two conductors is composed of an air gap and the outer plastic covering of the coax. Since the sleeve is loosly fit, the air gap is much bigger than the thickness of coax's outer plastic cover. Hence effectively the velocity factor is close to 1, and in most cases safely ignored.

    Translation from German to English (in red ink) added by me



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  • abcd567
    replied
    .
    @RIN67630:
    @rueckwaertsflieger:


    (1) My Tiny Tot, Kleinkind, Dipole: 6,8cm + 6,8cm

    (2) GROUNDPLANE ANTENNA MADE OF COAX ONLY - Without SO239 or N-Conector

    .

    Leave a comment:


  • RIN67630
    replied
    Oops, you ar right: I meant 65 mm or 6,5cm. It was a typo.

    I did not mean turning the sleeve back, but in a T-form.

    That is what i've made with regular Sattelite antenna cable, since I needed a longer cable:
    Beast4.jpg

    The wire and sleeve are just placed under the duct tape. This is a dirty construction placed inside a wardrobe under the roof. I will make a better antenna later, when the wheather permits.
    You may use other non conductive supports as e.g. gardening rods to support the construction outdoors.
    Using the original cable without the losses in the intermediate connectors shoud be good as well.
    Last edited by RIN67630; 2016-03-06, 17:27. Reason: fixed broken attachment

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  • rueckwaertsflieger
    replied
    Sleeve antenna

    Originally posted by RIN67630 View Post
    Would't it be much easier to trash completely the whip antenna and build a dipole with 6,5 mm of the core wire at one side and 6,5mm of the shield at the opposite?
    1 In case you are willing to increase your targeted antenna segment length 10 fold, you might have a chance. The length of both the active elments should be less than 69mm.
    2 The design you are targeting probably is just one kind of a sleeve antenna. Turning back the cable screen around the feeding coax with coating after stripping the cable coating for a magnitude of less than 65mm - around 45? depending on cable type - and using around 65mm inner conductor as whip. Theoretically you might get rather good results with this antenna. In practice the characteristics are defintitely sensitive to tiny changes in geometry. Further, you have to optimize length of shield folded back and whip experimentally. The screen has to be shorter than wavelentgh in free air by a factor near the velocity factor of the cable and so on.
    3 In case you will try this design, use very thick cable and a rigid sleeve. This will somehow make your design more robust. Probably you could choose Ecoflex 15 plus copper tubing 15mm for the sleeve, connected to the shielding.
    4 In case, you won't have success, go back to the cantenna design, turning out to be a somewhat sleeved antenna with dimensions such big, gaining much more robustness against mechanical variation.

    However, a not optimized sleeve antenna definitely will outperform the funny whip antenna provided with the electronics as long as you go close to half wavelength with both the active elements - in other words: do not try 6.5mm but less than 69.

    Good luck

    Leave a comment:


  • RIN67630
    replied
    By the way: did someone measure the velocity factor of the supplied coax cable?
    I can imagine, that a λ/4 T stub could well improve the overall sensitivity by short-circuiting the lower-band signals and avoid useless load on the RTL chip.
    Do you agree?

    Leave a comment:


  • RIN67630
    replied
    Originally posted by abcd567 View Post
    Your both points are worth considering.

    (1) Antenna length: length inside the base is a variable factor, depending on the manufacturer/design & worker who assembled the antenna (how much cable he left without braid). In the antenna I have, the total VERTICAL distance from the point where whip is screwed to base, up to the cable entry point is about 25 mm. If it is assumed that antenna length starts from cable entry point, then the whip should be chopped another 25mm i.e. 67-25=42mm. Since somewhat longer antenna is better than somewhat shorter antenna, I wont chop off entire 25mm. In fact couple of months ago I did the exercise below:

    Starting at 67mm whip length (as in the photo n my first post), I observed the maximum range this antenna brings in for few days. I then chopped it off by 5mm, again observed for a day, found improvement. I did a 2nd chop of 5mm, and observed for a day, found improvement. I then did a 3rd chop of 5mm, and observed for a day, found performance slightly decreased, so I stopped and did not chop any further. For my antenna 10mm chop seemed good, i.e. whip length 57mm instead of 67mm.

    Since your manufacturer may have a slightly different arrangement inside the base, you have also to repeat the stepped chopping exercise I have done to find best length for your whip.

    (2) Touching metallic base of antenna with the metallic can or plate is worth trying, and may improve performance. I have never tried it. If you peel off the circular plastic tape from bottom of antenna, bare metal will be exposed. Placing it on metal can or plate will make direct electrical contact. This is easy and worth trying.
    Would't it be much easier to trash completely the whip antenna and build a dipole with 65 mm of the core wire at one side and 6,5mm of the shield at the opposite?
    Last edited by RIN67630; 2016-03-06, 13:56.

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  • RIN67630
    replied
    Originally posted by abcd567 View Post
    STARTER
    (1) Whip is too long for 1090 MHz. Cut it to 67mm.
    The whip is made of an astonishly hardened steel. Use very strong plyers to cut it. I have almost ruined my electronic cutting plyer upon trying to shorten it!

    Leave a comment:


  • Adriaan25
    replied
    As a starter with this setup I've entered the "okay cool it works, now how can I increase range"-phase. So I'm following with increasing interest!
    I'd like to get experimenting with making cuts and extending the ground plane as well, which I will in a week's time ("unfortunately" got a holiday first).

    Thanks for your information so far abcd567 & others.

    Leave a comment:


  • abcd567
    replied
    FURTHER IMPROVEMENT
    Recently I opened the base of the magmount antenna (images 1,2 & 3). I noted that there is about 15 mm of vertical metal part between screwable whip and feed coax.

    This hidden vertical metal is part of antenna, and hence antenna length should be measured from the bottom of this part where coax is soldered to it. Since this part is 15 mm long in my antenna, my magmount's length was actually 67 mm + 15 mm = 82 mm. I therefore chopped off another 15 mm from the whip, making the length of removeable part 52 mm instead of 67 mm. See image 4. I noticed about 5% to 10% improvement.


    .
    Images 1, 2, & 3
    ..
    .
    .
    Image 4


    Things to be tried:
    1. Remove black plastic circular adhessive cover from bottom of antenna, and check electrical continuity between exposed metal base plate & the outer metallic part of MCX connector at other end of antenna's coax.

    2. Place exposed base on a metallic can and check if direct contact gives any improvement.

    Leave a comment:


  • abcd567
    replied
    Originally posted by Kpin View Post
    I would say the length should be measured from the end of the antenna cable - that is from where the core is free of the shield. And that is basically where the antenna cable enter the base.

    Another question: The bottom of the base is covered. Should this not be removed so that the small magnet base gets in full contact with the can/groundplane
    Your both points are worth considering.

    (1) Antenna length: length inside the base is a variable factor, depending on the manufacturer/design & worker who assembled the antenna (how much cable he left without braid). In the antenna I have, the total VERTICAL distance from the point where whip is screwed to base, up to the cable entry point is about 25 mm. If it is assumed that antenna length starts from cable entry point, then the whip should be chopped another 25mm i.e. 67-25=42mm. Since somewhat longer antenna is better than somewhat shorter antenna, I wont chop off entire 25mm. In fact couple of months ago I did the exercise below:

    Starting at 67mm whip length (as in the photo n my first post), I observed the maximum range this antenna brings in for few days. I then chopped it off by 5mm, again observed for a day, found improvement. I did a 2nd chop of 5mm, and observed for a day, found improvement. I then did a 3rd chop of 5mm, and observed for a day, found performance slightly decreased, so I stopped and did not chop any further. For my antenna 10mm chop seemed good, i.e. whip length 57mm instead of 67mm.

    Since your manufacturer may have a slightly different arrangement inside the base, you have also to repeat the stepped chopping exercise I have done to find best length for your whip.

    (2) Touching metallic base of antenna with the metallic can or plate is worth trying, and may improve performance. I have never tried it. If you peel off the circular plastic tape from bottom of antenna, bare metal will be exposed. Placing it on metal can or plate will make direct electrical contact. This is easy and worth trying.
    Last edited by abcd567; 2016-01-30, 08:25.

    Leave a comment:


  • Kpin
    replied
    Originally posted by Lufthansa View Post
    Yes, that's also a very good point. Where does the measurement starts? At the point where you screw the tip to the base of the antenna, or from the verry bottom of the base of the antenna to the point where you cut,.....
    I would say the length should be measured from the end of the antenna cable - that is from where the core is free of the shield. And that is basically where the antenna cable enter the base.

    Another question: The bottom of the base is covered. Should this not be removed so that the small magnet base gets in full contact with the can/groundplane

    Leave a comment:


  • F1Rocket
    replied
    The newer Nooelec antenna are tubular now. Besides the question of where to cut from, how about the hollow opening, does it affect anything? Thanks for sharing all of this knowledge, sure helps to get one up to speed.

    Leave a comment:


  • Lufthansa
    replied
    Originally posted by rueckwaertsflieger View Post
    Because before you have to take care about 3mm of antenna length you better should ask from where the λ/4 should be measured. As you might have noticed, the length from the can to the antenna tip is even more than λ/4. If you measure this length, things are different.
    Yes, that's also a very good point. Where does the measurement starts? At the point where you screw the tip to the base of the antenna, or from the verry bottom of the base of the antenna to the point where you cut,.....

    Leave a comment:

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