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

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?

--
John Popelish

"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.

Fred Bartoli wrote:

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.

Yep. Went right past me without even a whoosh noise. ;-)

--
John Popelish

If you have a good antenna do you _want_ to use a coil that's going to pick
up fields? I would think you'd want to control the energy getting into your
set.

What ever happened to buying a bottle of fancy whiskey and using the
cardboard tube it came in for a coil?

"John Popelish" wrote in message
...
Fred Bartoli wrote:

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.

Yep. Went right past me without even a whoosh noise. ;-)

--
John Popelish

Yes it is definitely a core T82-75 from the labeling on the package.
Which parameter specifies that it has low resistivity?
Can this be used as a transmission line transformer of a balanced mixer?

Which ferrite material works well for the AM band around 1 MHz?

I can get core #43, 61, and 63.


Thanks for the input folks.

A good mix is 61, There is a winding table for the different cores located
at www.crystalradio.us
Also there are plans listed. Cores are a easy way to get a respectable Q.
The worldwide crystal set contest starts this weekend look for info at the
site




"beginner" wrote in message
...
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