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

StellarCAT RXDesign at ssvecnet.com
Thu Nov 24 13:51:11 EST 2005

thanks... I just wish there was some consistency here... your saying something completely 
different than what all are saying. All replies now - maybe 6 of them - all of them left 
the reflector exactly where it was and most only adjusted the driver by a couple inches or so. 
Also all have bandwidths (this is the N - 85% full size) that are much closer to 300 than less 
than 200 as you say. 

on top of that a couple took each element off and adjusted it separately - had success doing this... 
but one found this to be inconsistent and just put everything where the manual says... all say it 
works extremely well and all say it covers the whole band essentially.

What do you mean when you say you "just adjusted the LL jumpers"??

the only thing I can come up with is the tram line is interfering. It is 2 guy cables that are suspended 
from about 60' on the tower - thus they form an angle across and in between the 2 elements... it HAS 
to be this as I have exhausted, literally, everything else. I am going to remove each element and test 
them separately on the tower at about 30'. 


  ----- Original Message ----- 
  From: K7LXC at aol.com 
  To: Force12Talk at qth.com ; RXDesign at ssvecnet.com ; towertalk at contesting.com 
  Sent: Thursday, November 24, 2005 11:14 AM
  Subject: Re: [Force 12 Talk] Mag 240N questions....URGENT 

  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 reasonable 
    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 got 
    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?  On 
    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 for 
    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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