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[TowerTalk] 6M coax balun

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Subject: [TowerTalk] 6M coax balun
From: "Jim Thomson" <>
Date: Tue, 31 Aug 2010 19:33:23 -0700
List-post: <">>
Date: Tue, 31 Aug 2010 18:37:35 -0400
From: "Roger (K8RI)" <>
Subject: Re: [TowerTalk] 6M coax balun

On 8/31/2010 5:10 PM, Hector Garcia XE2K wrote:
> Tony
> if you want to read more about the baluns for the 6m band and the antennas  go
> to this web page
> I just build the Hybrid for the LFA's and was very easy.
Part looks good, but the "air core" 5 turns on the paint can is unlikely 
to be very effective.


Roger (K8RI)

###   14 x  of the  large  type 43 beads..  [ 1" OD x .5"  ID  x 1.125"  long]  
  will give you 2083 ohms  on 6m.  If you use RG-393 coax,
you can then stuff  5 kw CCS all day long into it.   If you use large  type 31 
beads,  you will get  just over 2 k ohms, resistive, with 10 x large
beads... and  just over 4 k ohm, resistive, with 20 x large beads. [3 k with 15 
x beads] 

##  If you opt for a few turns of coax in a solenoid air wound config..... or 
coax wound on type 31  2.4"  OD cores.... make damn sure you keep the 
outside of the coax well  away from the boom... as in at least the OD of the 
coax coil.     IE:  3"-4" OD coil.... keep it 3-5" away from the boom...
or the stray C  from the coax to boom  will screw up the balun really fast.   
On these 80-40  baluns, made from coax wrapped onto type 31 cores,
depending on how tight the turns are wrapped onto the core..... it's not easy 
to get the coax  turns away  from the boom  [ or mast if a 80m rotary dipole is 
used] . 

##  This is where a large size nema box comes in handy.... then the cores and 
coax can be suspended in mid air, dead center in the nema box...and away from 
The string of large beads on RG-213/393  coax has an advantage too....easier to 
install..and zip windload.  You also don't have a stray C to boom problem.  You 
can't blow
up the large type 43 beads..on any band..with YC-156 power levels.    The large 
type 31 beads will also work.. but the choking Z has to be a lot higher, since 
the type 31
material  is mostly resistive.  I squared x Resistive ohms  = real heat     I 
squared  x  reactive ohms = reactive power =  'wattless power' .    It amounts 
to a 2 x edged sword. 
Modern thinking dictates a predominantly resistive component, but to pull that 
off, the Z has to be real high... like 2-3+ K  ohms.    A type 31 choke balun 
that's only 1 k ohm,
and predominantly resistive, will go off like a bomb.  A  2 k ohm choke, also 
made from type 31 material, will  dissipate exactly  1/2  the power of a 1 k 
ohm/type 31  choke. 

I will be doing some experiments this fall/winter, where type 43 beads are used 
at the feedpoint... and type 31 beads are used 1' downstream. 

Later... Jim   VE7RF         


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