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coil loaded antenna for 108Mhz - inductor value, design

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deepak007

deepak007

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coil loaded antenna

hello

could anyone tell me how to design a (center/base) coil loaded antenna for 108Mhz? what should be the inductor value. please give me a simple design technique.


i recently saw a video on metacafe( here is the link -- https://www.metacafe.com/watch/1386024/mr_microphone_hack/) . it is shown in the video that a quarter wave wire antenna is wound on a small bolt, to conserve space(for a transmitter bug). will it really work?
 

Re: coil loaded antenna

**broken link removed** is a link to a whole page of utility programs, including antennas. These are in DOS.

As far as the antenna which is all coil, this is a form of helical antenna. The problem is that the radiation resistance is very low and the efficiency poor because of the other loss components, such as skin resistance.
 

    deepak007

    deepak007

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Re: coil loaded antenna

Sorry to say, but that coil-over-bolt antenna :D from the movie, hard to believe is a Helix antenna.

Helix antenna in normal-mode have a specifically spacing and pitch angle between turns (and no metal core inside).

In my opinion from how was realized, was just lucky that radiates some power in the broadcast band.
 

Re: coil loaded antenna

thanku Mr.vfone! could you tell me how i can calculate the spacing and angle of the helix antenna for FM band?
 

Re: coil loaded antenna

i want to make a small tx bug in a matchbox.the transmitter has a 7000 microvolts field strength, at a distance of 3meters.
to make things simple,if i take a quarter wavelength wire antenna, and wind it (closely) on a pencil or wooden dowel, will it work? i am just trying for a range of one or two blocks with the tx. will it be sufficient?
 

Re: coil loaded antenna

A quarter-wave length monopole antenna if doesn’t have proper ground plane, and if is bent or rolled, will loose the radiating performance.
Its true, sometimes don’t need to get the best performances to make it work in an application like this. Just try it.

Also you can make a loop antenna:
**broken link removed**
 

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