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[TowerTalk] EF140s element tuning on F12 C4

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Subject: [TowerTalk] EF140s element tuning on F12 C4
From: K7LXC@aol.com (K7LXC@aol.com)
Date: Sat, 17 Oct 1998 09:32:10 EDT
In a message dated 98-10-16 19:48:31 EDT, n6rfm@gis.net writes:

> Just finished putting together a C4.  Can anyone comment on the expected 
> VSWR changes for the 40M element as the antenna is raised.  At five feet,
the 
> EF-140S is low at about 6.65 MHz.  I can move the linear loading jumpers way
> out to bring the antenna up to 7.08 MHZ, BUT the jumper locations are out at
> about 35 inches not 14-18 inches as specified.  Should I just wait until
it's 
> "up the tower" to make the adjustments or raise the antenna to a higher
level 
> (10 - 15 feet ?) and try again ?  

      Start with the factory dimensions. You get big added capacity from the
close proximity to the ground which will make it generally resonate low.
Raising it 10-15 feet still isn't high enough to eliminate ground effects.

      I've never worked with a Force 12 linear loaded antenna that was exactly
right when set to the factory dimensions. There are your starting point.  

> Am I just too close to the ground to get an  accurate measurement ?  

      Yes.

> Adjusting this element after the antenna is on the  mast looks tricky !

       It's not. You need a 5/16" nutdriver and an antenna analyzer to get it
done. Measure the feedpoint with the coil installed and you'll be able to get
it dialled in.

Cheers,  Steve   K7LXC
      

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