Topband: Core for K9AY loop transformer

Richard L. King k5na at
Tue Mar 27 22:05:48 EST 2007

At 20:19 3/27/2007, Tom Rauch wrote:
> >>In looking on the FAIR RITE web page I see that type 43
> >>material is
> >>spec'd for freq range 25-300 Mhz.  So why use a material
> >>for that
> >>range...what gives?..
> >
> > When you use a ferrite to wind a transformer, you want LOW
> > loss.
> > When you use a ferrite for suppression of RFI, you want
> > HIGH loss.
> > The Fair-Rite catalog is listing this as a suppression
> > part, and 25-
> > 300 MHz is the range where it has relatively high loss. It
> > is a low
> > loss part below 10 MHz, and thus a fairly good choice for
> > winding
> > Beverage transformers.
>It really depends on the specific application. If it is a
>closely coupled winding, a transmission line transformer, or
>broadband transformer we generally want a core with an
>impedance peak around the lowest part of the operating
>frequency range. This is generally true for receiving
>If it is a resonant circuit we generally want high Q, or a
>low loss tangent compared to the impedance, at the operating
>frequency. The same is true if the core handles high power.
>If it is a suppression device we generally want high
>resistance compared to reactance.
>I almost exclusively use 73 materials for broadband .5 to
>30MHz receiving applications.
>73 Tom

I use a pair of large type 43 toroids with 10 turns of RG6 feedline 
through them for my common mode suppressors on my Beverages.

Are you saying this is a poor choice?

73, Richard - K5NA

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