Topband: Core for K9AY loop transformer

[Tom Rauch]

>>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 
applications.

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