Telescoping antenna -- why is there a knob on top?

  • Context: Undergrad 
  • Thread starter Thread starter hacivat
  • Start date Start date
  • Tags Tags
    Antenna Radio Rf
Click For Summary

Discussion Overview

The discussion revolves around the purpose of the knob at the end of telescoping antennas, particularly in the context of amateur radio. Participants explore various potential functions of the knob, including practical handling aspects and technical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the knob is primarily for ease of handling or to prevent the inner sections of the antenna from slipping inside.
  • Another participant humorously suggests that the knob is there to protect eyes.
  • Some participants agree that the knob serves both practical functions: making it easier to extend the antenna and preventing loss of inner sections.
  • A participant mentions that the knob has historical significance, indicating it was used for static dissipation before telescoping antennas were common.
  • Another participant discusses the role of a ball or capacity hat on antennas, noting its effect on reducing corona discharge noise and its relevance to antenna resonance.
  • One participant clarifies that static discharge is less of a concern for receiving antennas since they should be grounded through the receiver.

Areas of Agreement / Disagreement

Participants express a mix of views regarding the knob's purpose, with some agreeing on its practical uses while others introduce technical aspects that complicate the discussion. No consensus is reached on a singular purpose.

Contextual Notes

Some assumptions about the technical functions of the knob and its historical context remain unresolved, and the discussion includes varying perspectives on its significance.

hacivat
Messages
28
Reaction score
3
TL;DR
Does the knob at the end of a telescopic antenna have a significance?
This is probably a trivial or even a stupid question, the reason I am writing here is I couldn't find something satisfactory online. I am a new amateur radio operator. Currently enjoying listening to SW and MW bands. I have a nice radio receiver with a long telescopic antenna. I have noticed that the knobs at the end of telescopic antennas sometimes come in different sizes. Are they there only for ease of handling when increasing the length of antenna or preventing the end from slipping inside? Or do they have a significance in terms of some technical detail like introducing a capacitive load or so?
 
Physics news on Phys.org
They are there to protect your eyes.
 
  • Like
  • Informative
Likes   Reactions: rude man, Spinnor and Keith_McClary
hacivat said:
Summary:: Does the knob at the end of a telescopic antenna have a significance?

Are they there only for ease of handling when increasing the length of antenna or preventing the end from slipping inside?

Both ... something easy to hold whilst extending the antenna and definitely to stop the inner tubes from disappearing inside
 
  • Like
Likes   Reactions: Spinnor
hacivat said:
Summary:: Does the knob at the end of a telescopic antenna have a significance?

preventing the end from slipping inside?

Baluncore said:
They are there to protect your eyes.
Both, I should say. Lose the inner one down the inside and you may never get it back.
 
sophiecentaur said:
Lose the inner one down the inside and you may never get it back.
Tweezers and needle-nose pliers. Don't ask me how I know.
 
  • Like
  • Haha
Likes   Reactions: berkeman, jim mcnamara, Keith_McClary and 2 others
Vanadium 50 said:
Tweezers and needle-nose pliers. Don't ask me how I know.
It is also easier if you apply copious and creative swearing before you start in with the grasping tools.
 
  • Like
  • Haha
Likes   Reactions: davenn and sophiecentaur
They were there long before the antenna became telescoping. Static dissipation. all the rest of the answers are also valid, but, now you know it's a there for a real function to the radio. A point would allow rapid discharge rather than slow bleed off. That rapid discharge would equate to noise and audio bursts inside the the radio.
 
  • Like
Likes   Reactions: alantheastronomer
raysmith said:
They were there long before the antenna became telescoping.
A ball or a capacity hat on a vertical whip transmitting antenna reduces corona discharge noise. The capacity hat also reduces the length of whip antenna needed for resonance.

The OP specifically referred to a radio receiver with a telescopic antenna. Static discharge is not a problem on receive because the antenna should be deliberately grounded through the front end of the receiver.
 
  • Like
Likes   Reactions: coolul007

Similar threads

  • · Replies 37 ·
2
Replies
37
Views
4K
Replies
10
Views
4K
  • · Replies 6 ·
Replies
6
Views
5K
  • · Replies 5 ·
Replies
5
Views
4K
  • · Replies 10 ·
Replies
10
Views
4K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 13 ·
Replies
13
Views
5K
  • · Replies 4 ·
Replies
4
Views
9K