How good is ferrite 75 material for crystal AM radio?
 

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.

beginner wrote:
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.

I wouldn't use ferrite at all for this application. A suitable iron
powder core would be a lot better:

http://www.amidoncorp.com/aai_ironpowdercores.htm

One of the #15 material cores would be ideal.

Leon
--
Leon Heller, G1HSM
Email:
My low-cost Philips LPC210x ARM development system:
http://www.geocities.com/leon_heller/lpc2104.html

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.

I wouldn't use ferrite at all for this application. A suitable iron
powder core would be a lot better:
=================================
Am I getting confused ? I thought the designation T82-75 identifies a
powder iron toroid , having a 0.82 inch outer diameter and is made of 75
type (mix)of material.
If ferrite it would be labelled FT82-75.

In my file I keep a snippet from QST ? in which Zack Lau (ARRL Lab)
highlights identification of Ferrite type of materials as follows:
Quote ---------------------------------------------------------------------
-----------
You may be able to grade your ferrites by resistivity. Just stick an
Ohmmeter across or bead in question and measure its resistance.
The readings you'll may not be narrowly definitive ,but if your parts
collection contains toroids of only a few types ,you may be able to separate
one mix from another according to Table 2.

Table 2
Typical Resistances of Small Ferrite Beads/Toroids

Material / Resistance
43 10 MOhm
61 30 MOhm
63 30 MOhm
64 30 MOhm
72 30 MOhm
73 20 KOhm to 100KOhm
75 5 KOhm to 20KOhm

Note by WJ1Z : It's a good idea to color-code your ferrite materials as you
require them (example : mix 43= red , mix61 =blue ,
mix 75 = green . When your cores arrive ,segregate them by mix and working
with each type in turn ,spread each lot on a sheet of newsprint and
spray-paint them (one face will will do) according to your color code .
Be sure to record and save the key !

Unquote --------------------------------------------------------------------
---------------

From the above table it shows that with its relatively low resistivity ,mix
75 contains relatively much iron ,which indicates the material is suitable
for low frequencies only , perhaps even not RF.

Frank GM0CSZ / KN6WH

Frank Dinger wrote:

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.

I wouldn't use ferrite at all for this application. A suitable iron
powder core would be a lot better:

=================================
Am I getting confused ? I thought the designation T82-75 identifies a
powder iron toroid , having a 0.82 inch outer diameter and is made of 75
type (mix)of material.
If ferrite it would be labelled FT82-75.


The OP said it was ferrite. Assuming he is referring to an Amidon
product 75 is a ferrite mix:

MATERIAL ' J '/75 ( µ = 5000 ) Low volume resistivity and low core loss
from 1 KHZ to 1MHz. Used for pulse transformers and low level wide band
transformers. Excellent frequency attenuation from 0.5 MHZ to 20 MHz.
Available in toroidal form and ferrite beads as standard off the shelf
in stock. Also available in pot cores, RM cores, E & U cores as custom
ordered parts with lead time for delivery.

I'd say this was quite unsuitable for his purpose. It would be OK for a
wide-band transformer, as he suggests.

Leon
--
Leon Heller, G1HSM
Email:
My low-cost Philips LPC210x ARM development system:
http://www.geocities.com/leon_heller/lpc2104.html

It is FT82-75 and the resistance is only 5 KOhm, so the mix is accurate.

I will have to make use of them in wideband tranmission transformers.
Can you folks suggest a frequency range?

I can get ferrite #61 or #63, but iron core only comes in mix #2 or #6
locally.

Thanks for all the help!




Table 2
Typical Resistances of Small Ferrite Beads/Toroids

Material / Resistance
43 10 MOhm
61 30 MOhm
63 30 MOhm
64 30 MOhm
72 30 MOhm
73 20 KOhm to 100KOhm
75 5 KOhm to 20KOhm
The OP said it was ferrite. Assuming he is referring to an Amidon
product 75 is a ferrite mix:

MATERIAL ' J '/75 ( µ = 5000 ) Low volume resistivity and low core
loss from 1 KHZ to 1MHz. Used for pulse transformers and low level
wide band transformers. Excellent frequency attenuation from 0.5 MHZ
to 20 MHz. Available in toroidal form and ferrite beads as standard
off the shelf in stock. Also available in pot cores, RM cores, E & U
cores as custom ordered parts with lead time for delivery.

I'd say this was quite unsuitable for his purpose. It would be OK for
a wide-band transformer, as he suggests.

Leon

beginner wrote:

It is FT82-75 and the resistance is only 5 KOhm, so the mix is accurate.

I will have to make use of them in wideband tranmission transformers.
Can you folks suggest a frequency range?

I can get ferrite #61 or #63, but iron core only comes in mix #2 or #6
locally.

Mix #2 should be OK for your crystal set.

With a transmission line transformer you should be able to go up to 100
MHz or more, the core is only important at the lower part of the
frequency range.

Leon
--
Leon Heller, G1HSM
Email:
My low-cost Philips LPC210x ARM development system:
http://www.geocities.com/leon_heller/lpc2104.html

beginner wrote:

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.

Go to the makers catalog (available as a big PDF) at:
http://www.fair-rite.com/fr_catalog-14thed_rev3.pdf
and read about the various types (starting with the parametric
comparison on page 4, including the frequency recommendations under
the low flux density row). Type 43 is normally used in RFI absorbing
devices but has pretty good properties for indictors for low flux
applications up to 10 MHz. Type 60 is recommended for up to 100 MHz,
and type 63 isn't a Fair-Rite type listed in this catalog. In the
same table type 75 is limited to .75 MHz for low flux applications.
Based on this table, alone, I would probably try the type 43.

--
John Popelish

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


Here's what seems like a hi-Q a crystal set using toroids:
http://www.crystalradio.net/contest/paul.html

It uses "two toroid cores, Palomar Engineering T-130, broadcast band
frequency material". Unfortunately it doesn't say the kind of core, but from
the number of turns and the capacitance I figured that it must be type 26
(yellow/white). I think this is a rather uncommon kind of material, it has
one of the highest mu's, 75, compared to mu=10 for type 2 and mu=8 for type
6. Anybody with experience with this kind of material?

Sverre
LA3ZA

In article ,
beginner wrote:
It is FT82-75 and the resistance is only 5 KOhm, so the mix is accurate.

I will have to make use of them in wideband tranmission transformers.
Can you folks suggest a frequency range?

I can get ferrite #61 or #63, but iron core only comes in mix #2 or #6
locally.

Thanks for all the help!

Digging out an old Amidon spec. sheet, they used #61 and #33 for their
ferrite (antenna) rods. Type #61 for medium wave and up to 10 MHz, and
type #33 for VLF.

The real question is "Are you using it in a tuned circuit?", where you
want the coil loss to be negligable. If you're making an antenna coil
that's tuned with a capacitor for AM broadcast (.54-1.7 MHz), use the
type 61.

For wideband transformers, where frequencies are higher than tuned
circuit use, Amidon specs type 61 as good for 10-200 MHz, and type 63
as good for 25-200 Mhz. For HF use #43, #77, #72, or #F.

Mark Zenier Washington State resident

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