TopBand: 160m Beverage transformer core material?

[Tom Rauch]

> Date:          Tue, 07 Apr 1998 11:27:17 -0500
> From:          Rick and Angela <anelson@dbtech.net>
> Subject:       TopBand: 160m Beverage transformer core material?
> Wondering what fellow top banders are using in the way of core material
> (mix), type, and size for their 160m beverage antenna matching

Hi Rick,

This has been covered before, but let me briefly repeat some 
important points.

What you want is a core material with an ui (permeability) that 
has the highest possible value on 160, and gradually decreases 
at higher frequencies. That insures the transformer has the highest 
possible winding impedances with the least amount of turns. 
Minimizing turns minimizes the undesired stay capacitance, and that 
capacitance hurts high frequency response and increases unwanted 
primary to secondary common mode coupling. 

Do not, despite recommendations in Beverage handbooks, use that silly 
ui 10,000 material. That material actually requires MORE turns on 
160, and has poorer performance than most other lower initial 
permeability materials.

Look at the core impedance at 160, not at DC (like others must have 
done) and select a material that PEAKS on 160...not at a few hundred 
kHz!!!!

I generally use 73 (ui 900 @ 2 MHz) or 43 (ui 900 @ 2MHz) mix cores 
in broadband HF systems.

 If the transformer is resonant then you have to consider an even 
lower perm core. Core Q becomes important. In a resonant system you 
often want to select the highest Q core, rather than the ui peak.    

A Faraday shield is a waste of time with a properly designed 
transformer, and of questionable benefit under any condition. 

73, Tom W8JI
w8ji.tom@MCIONE.com

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