[TowerTalk] [Force 12 Talk] Mag 240N questions....URGENT

K7LXC@aol.com K7LXC at aol.com
Thu Nov 24 13:14:12 EST 2005

In a message dated 11/24/2005 10:00:45 A.M. Pacific Standard Time,  
Force12Talk-request at qth.com writes:

>  I am TRYING to "tune" a 240N (height is 25') and am not  getting 
results. Tom is not sure why. He says the factory  default lengths for the 
reflector and the driver should work but I am much  shorter than this (5.5" 
on each tip on the reflector and  ~3.5" on  the driver element) AND the 
bandwidth is bad (~ 180 Khz - should be almost  300). Can someone please 

>  Does anyone know how many  turns the hairpin match has? I do not think I 
one (or I misplaced it)  and I made one that is 2.5" in diameter and 3 turns.

Since the hairpin (made into a coil) is part of  the element length, it's not 
too critical in length since the jumpers can  (will) be adjusted to resonance 
anyway, rendering the hairpin length  simply relative. 
>  Did you tune yours or just set it to a length?

You have to tune each element to resonance (the  REF and DIR resonances are 
in the manual). I have NEVER seen an F12  linear loaded antenna be set 
correctly when using the manual dimensions -  they're just a starting point. 

>  What length did you end up with (for the tip sections) on  the reflector?  
the driven element?

I've always just adjusted the LL jumpers and  didn't worry about any other 
part of it. 

>  What is the swr bandwidth for a 2:1?

For the F12 LL antennas I've worked on - a  couple of dozen - it's been about 
180 khz. I think there were only a couple of  N types in there. 

>  I checked the driver alone (reflector jumper removed) and  still the SWR 
a 2:1 is only about  180Khz.

    Sounds normal to me. 
Steve    K7LXC
Professional tower services for commercial and amateur
Cell: 206-890-4188

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