×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How does the near field off end of rubber duck decline?

How does the near field off end of rubber duck decline?

How does the near field off end of rubber duck decline?

(OP)
Most radio controlled model airplane folk "believe" that a rubber duck antenna on their transmitter radiates best off the end, so a common saying is passed around: "pointing a whip at the model is bad; pointing a rubber duck is good."  Clearly, the far field off the end of rubber duck antenna is a null.  The literature is quite clear.  For the far field it behaves as a short monopole.  However, the people become "believers" because they test out their trasmitter (72 Mhz) at relatively short distance, e.g. 50 feet (roughly 4 lambda) and find that the rubber duck works best pointed at the plane/field-strength meter, etc. and the whip does not.  For example--
http://www.bergent.net/antenna_field_test.html

How do the near field effects drop off with the small helix, compared to the whip?  (Or, what would be a simple demonstration that pointing a rubber duck at the model produces the weakest signal.)

RE: How does the near field off end of rubber duck decline?

For small antennas, the material around them shapes the antenna pattern. For larger antennas, it's the antenna itself that shapes the pattern.

I'd expect that reflections off the ground or human reradiates more from the duck and fills in the null off its' end.

You won't see near field effect more than a wavelength or two away. I've seen monopoles and dipoles used for heating human tissue and the tips of these do an equivalent amount of heating as the high current points.

kch

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources