There is no such thing as a single core type suitable for "general" HF
use, because the required core material depends strongly on just what
the use is.

You can, however, satisfy a large number of requirements with a few core
types. Micrometals type 2 or 6 powdered iron cores are suitable for most
high-Q inductors. I consistently measure higher Q with type 6 cores, at
least when sparsely wound, but type 2 is convenient for higher
inductances due to its higher permeability. I didn't know Philips made
powdered iron cores -- if they do, you should check their web site and
Micrometals' to find an approximate equivalent. The choice of core
material for RF chokes and broadband transformers depends on how much
power and how much DC current is involved. For low power applications
where there isn't a substantial amount of DC current, Fair-rite type 43
ferrite material is a good choice for those applications. If you need
more impedance, for example at lower frequency or in higher impedance
circuits, one of the 70 series materials would be better. Again, look at
the respective web sites to find an approximate equivalent material from
another manufacturer.

The sizes of cores you'll need depends on the inductance (for high-Q
inductors) or impedance (for RF chokes or broadband transformers) range,
power handling capability, and DC flux level you need to deal with. For
low power, low flux applications, (F)T-37 and -50 are popular sizes.
These are 0.37 and 0.50 inch OD respectively.

Roy Lewallen, W7EL

tictac1 wrote:
Hi,

I need some toroidal cores(powdered iron or ferrite) for general HF
use. So i guess i will be looking for cores in 3-30~ MHz range. I have
access to Philips toroidal cores in where i live and i need your advice
to find the suitable one. Waiting for your answers...

Thanks...