Hello Telamon.

Thanks for your reply.

Just a question, you say "the needed inductance will be in the frequency
range you are interested in blocking", but what is the needed
inductance? As high as possible, a low as possible, a defined value?

I have seen things like "Impedance: 100 at 25MHz, 200 at 100MHz". I'm
only interested in lower frequencies, in the shortwave band.. Also
bigger ferrites has higher inductace.


Thanks!

Best regards.


Telamon wrote:
In article , Nacho
wrote:


Hello.

I need some help from you.

I live in a big city and shortwave is very noisy. But the main noise
comes from my own house, specially the computers.

I have been trying to reduce the interferences using ferrite and iron
powder chokes.

I have been playing with two kind of chokes: one is the typical
toroidal iron powder, painted choke, and the other is like a ferrite
choke in a hollow cylinder, divided in two part in a plastic case,
that can be put in a cable without disconnecting it.

Some noises are reduced best when I use the torodial choke (like in
the AC currect cable to the receiver) and other noises are reduced
with the cylindrical choke (like in the computer cables, specially
the keyboard).

I prefer the cylindrial ones because it is much easier to put. For
keyboard cable, it works great, so I plan to buy some in a electronic
shop.

Can you give me some recommendations about them? I want to buy some
big and some small (if they are cheap, I don't know the price). For
the keyboard of my brother's computer, with one cylindrical the noise
disappears (it is two rooms far) but my computer needs more with
one cylinder the noise is reduced but doesn't disappear, as it is
much nearer.

Any recommendation will be great.


Go for the Ferrite as it has more inductance per turn since you only
have one to three turns at best depending on type.

Not any ferrite will do. You need to look at its specifications so the
needed inductance will be in the frequency range you are interested in
blocking.

The cylindrical ones are good from the stand point of the input to
output has greater separation so the noise has a harder time making it
around the core.

If you are going to put more than one core on a electrical cord start
with them on both ends since there could be drivers on both ends like
on my computer.

Good luck in improving your reception.