RadioBanter - View Single Post - How good is ferrite 75 material for crystal AM radio?

January 23rd 04, 07:37 PM

"John Popelish" a écrit dans le message news:
...
beginner wrote:

I made an inductor by winding 14 turns on T82-75 torroid.
Using 180 pF variable capacitor, in a crystal radio circuit I could not
pick up any signal but even with a 470 uH modded inductor I picked up a
few
signals.

Is this material not suitable for this appication?

Thanks

I am not familiar with this core number, but if it is actually made of
Fair-Rite type 75 ferrite, it is not very good for making 1 MHz
inductors. It is low resistivity (acts as a loaded turn in parallel
with your inductance) and quite a bit of hysterisis loss. Are you
sure it is ferrite? Can you measure the contact resistance between
two points on the core with your ohm meter?

--

Whatever the material, a core shape is not well suited to pickup fields.

Instead, use an opened one, like ferrite sticks. Unfortunately you'll have
to have many more turns.

Fred.