[TenTec] 238 "Tuner" Balun

[Steve Hunt]

As others have said, the internal balun is a 4:1 voltage design - a 
better option is a 1:1 current balun.

I use my TT238 tuner with an external 1:1 current balun comprising 11 
turns on two stacked FT240-52 cores. CM performance charted here:
http://www.karinya.net/g3txq/temp/52_mix.png

Type 43 material would be better for the lower frequency bands, or Type 
31 if you're trying to cover down to 160m. Performance charts are here:
http://www.karinya.net/g3txq/chokes/

with some more extensive data here:
http://www.karinya.net/g3txq/chokes/type31.jpg
http://www.karinya.net/g3txq/chokes/type43.jpg
http://www.karinya.net/g3txq/chokes/type52.jpg

The winding doesn't need to be coax because we typically are not trying 
to preserve a 50Ohm impedance through the balun. Using bifilar windings 
with PTFE insulation will provide a higher voltage withstand capability.

Balun Designs has a model similar to the one I am using:
http://www.balundesigns.com/model-1161-1-1-atu-current-balun-3-54-mhz-5kw/

Steve G3TXQ



On 28/12/2017 02:10, Bob Good wrote:
> The Ten Tec manual has virtually nothing to describe the internal balun supplied with the unit.  I do not know how to physically look to tell its design.  Is it a 1 to 1 or a 4 to 1;  Current or Voltage design?  Okay, if it is 4:1 or voltage design, please comment on the proper  design in schematic form or picture; what ever it takes for me to wind a current design, 1 to 1 balun.  Can the toroid be reused?  I use it on a ladder line, center fed 135 ft. dipole up 60 ft.  Other antennas are coax fed.  Thanks to all who would like to help this analog old timer.  Happy New Year and ‘73.  Bob K4BG.  (Good on QRZ)
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