Hey group,

I was looking for a cheap source of toroids and stumbled across a
blown ATX computer power supply. It was chock full of toroids.

I've attached a picture and used a chapstick stick as a size
reference.

While I have everyones attention, let me repost my question posted to
the shortwave group. It may be better addressed in here.

-------------------------------------------------------------------------------------------------------------

Got a few questions concerning the fabrication of an antenna tuner.

I am using Arnie Coro of DX Unlimited's instructions for a simple PI
network tuner.

http://www.radiohc.org/Distributions.../pi-tuner1.htm

Instead of a 10 position switch I am using a 2 pole 6 position switch
then fliping a toggle to use the other 6 positions for a total of 12
inductance settings. But thats not my question.

My question is:

Given the small size of the box this all is going to fit into, I would
like to use a torroidal core instead of an air core.

1) Does Radio Shack sell torroidial cores?

2) Would I wind it similarly to the air core in that each winding is
separated by one wire width and tapped every 3rd turn?

If I understand the concept correctly, it's seems the PI network tuner
tunes both ends of the equation. This would be good as I am using a
Sony ICF-SW7600GR and dont have a clue what the input impedance might
be.

3) Is that how it really works? Tuning both the antenna and the line
out to the receiver?

Arnie says this tuner will work down to 5kHz. And given my research of
this tuner type, I would need to switch in extra capacitance to get
down low for say the AM band. I am considering adding in a few more
toggles to achieve this. My variables are 365pf.

4)How much extra capacitance would be needed? And would this be
practical or should I switch in another inductor creating a PI-L?


Thanks in advance,

Mike

mike wrote:
I was looking for a cheap source of toroids and stumbled across a
blown ATX computer power supply. It was chock full of toroids.

Probably powdered iron cores and not very useful at RF frequencies.
--
73, Cecil, W5DXP

On Fri, 19 Sep 2003 12:31:56 -0700, Cecil Moore
wrote:



I was looking for a cheap source of toroids and stumbled across a
blown ATX computer power supply. It was chock full of toroids.


Probably powdered iron cores and not very useful at RF frequencies.

Yep your right. I found them to be mostly very high Al....totaly
useless at RF frequencies.

mike

On Sat, 20 Sep 2003 09:43:02 GMT, "Bill" wrote:

Good source of roids can be found:

http://www.kitsandparts.com

See Diz, he's the Toroid King! grin


Cool link. Thanks. Guess I can buy em in bulk and sell the rest on
EBAY grin

mike

High Al (high permeability) ferrites are very useful at RF. They're
widely used for broadband transformers, baluns, and EMI suppression
chokes, and are in fact very often the best choice for those
applications. If DC current is low enough to avoid saturation, they also
make excellent RF chokes -- ones that maintain a high impedance over a
very wide bandwidth and don't show any appreciable self resonant effect.

The only RF application they're not good for is inductors in tuned or
high-Q circuits, such as filters and tank circuits, or as tuned
transformers.

Roy Lewallen, W7EL

mike wrote:
On Fri, 19 Sep 2003 12:31:56 -0700, Cecil Moore
wrote:




I was looking for a cheap source of toroids and stumbled across a
blown ATX computer power supply. It was chock full of toroids.



Probably powdered iron cores and not very useful at RF frequencies.


Yep your right. I found them to be mostly very high Al....totaly
useless at RF frequencies.

mike

On Sat, 20 Sep 2003 18:01:45 -0700, Roy Lewallen
wrote:

High Al (high permeability) ferrites are very useful at RF. They're
widely used for broadband transformers, baluns, and EMI suppression
chokes, and are in fact very often the best choice for those
applications. If DC current is low enough to avoid saturation, they also
make excellent RF chokes -- ones that maintain a high impedance over a
very wide bandwidth and don't show any appreciable self resonant effect.

The only RF application they're not good for is inductors in tuned or
high-Q circuits, such as filters and tank circuits, or as tuned
transformers.

Roy Lewallen, W7EL



Thats what I figured. I have kept them for this very purpose.

mike