Spiral antenna on cars

Status
Not open for further replies.
B

bobilgner

Newbie level 5
Joined
May 12, 2009
Messages
10
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Visit site
Activity points
1,366
Some cars have a whip antenna with a spiral of wire attached to the stalk of the antenna, as per the attached picture.

I have read (on various groups) that the spiral is there to reduce wind resistance and noise, alternatively that it covers AM reception as opposed to the content of the stalk covering FM reception.

Does anyone have a good reference to the correct answer. What is this spiral around the whip antenna?
 

Attachments

  • Spiral_on_antenna.jpg
    2.1 MB · Views: 96

The spiral will aid wind load shedding and hence flexing of the main element. When you drive along, the aerial gets a high pressure on its front and low pressure on its rear, because the main aerial is round this is not a stable state and the pressure areas move from side to side, imparting a sideways force on the aerial, causing it to oscillate sideways. The external spiral causes the air flow to be directed and hence stable.
The wind load shedding phenomena caused a 1000 feet tall Emley Moor TV mast to fall down in 1968. The mast went into oscillations.
Frank
 


That does make sense. I have seen the wild oscillations on the stubby antenna used by the Le Mans Porsches. The rapid oscillations resulted in a blur where the antenna was positioned. I was wondering whether this rapid oscillation would have an effect on the tx or rx of the telemetry. Probably not.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…