[amsat-bb] Re: Determining the length of a driven element

Joe nss at mwt.net
Sat Aug 23 06:33:25 PDT 2008


Phil wrote:

>During a casual conversation recently, the topic of aerial trimming came up. 
>Perhaps this may be a little off-topic here but since I don't know the answer 
>I thought this would be a good place to ask anyway.
>Say a dipole has an SWR of 5:1 at one end of a band and 4:1 at the other end. 
>Further, let's say that the dipole will be used at the centre of the band and 
>with a reasonable SWR. It has been determined that the dipole needs to be 
>shortened. The question is by how much?
>The person asking the question is reluctant to pull the aerial down a dozen 
>times so that short lengths can be nibbled off each end and instead wants to 
>know if the amount that needs to be cut off can be determined from the 
>difference in the SWR at both ends of the band.
>A logical question I suppose but is there a reasonable answer?

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