No announcement yet.

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

  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    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


    • #17
      Originally posted by abcd567 View Post
      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?


      • #18
        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.