On Sun, 25 Jul 2010 08:13:20 +0100, "David Looser"
wrote:

"Paul G." wrote

I had considerable trouble with a cable feed causing hum and bizarre
behaviour with a Linn CD player and power amp.

You have a cable feed to a CD player?

No..... but the audio system shares a ground with the FM tuner
which has a cable connection. The CD player (Linn Karik & Numerik)
would do strange things now and then, until the cable connection was
removed. Our cable must have some pretty weird stuff on it, as many
other audio devices would hum or behave oddly when they shared a
ground with the cable.

I am not aware of any common commercial RF isolator for this
purpose. Maybe its an opportunity for someone to market it as a cure
for some of the weird effects you get when tied into cable.


So called "Braid-breakers" have existed for many years to help keep out
interference picked up on the braid of a TV or FM radio downlead. They work
in a similar way to what you have described, ie. a small ferrite-cored
transformer.

David.


There must be a variety of types of "braid-breakers"... Most of what
I see are mentioned on the internet are (ASCII circuit) :

C1
in1-------.-----||------.------- out1
) )
)L1 )L2
) )
) )
in2-------'-----||------'------- out2
| C2 |
| |
| |
'-/\/\/\/\/---'
R1
R1= a few megohms (needed to bleed current to avoid hi-voltage
buildup)
C1,C2=5-10pf
L1,L2= few turns of wire (not coupled to each other)
To see the ASCII circuit properly, you need a fixed width font like
"courier"
This circuit works at the UHF frequencies, but doesn't respond well
to VHF or lower frequencies. It will definitely clean up any powerline
frequencies.

The RF isolation transformer I mentioned above is referenced a few
times as a braid breaker. With a suitable toroid transformer (like
what you can pull out of a splitter) you should get very good
isolation and uniform response from VHF to well beyond UHF.

I asked around for such a device at TV/electronics stores here in
Nova Scotia (Canada), no one had a clue what I was talking about.

Paul G.