Here in Ohio wrote:
On 19 Nov 2006 15:49:13 GMT, Walt wrote:
wrote:
If RFI is a problem (and it isn't in the vast majority of home
installations), the way to deal with it is through 1) balanced inputs,
Balanced inputs on audio equipment
almost never have significant common mode rejection at radio frequencies.
This is the first time I've ever heard anyone say this. Do you have a
cite?
My guess is that RFI will not be reduced by using a balanced input.
My guess is otherwise. Of course, I'm not really guessing.
Unless the RFI signal is predominantly positive or negative
(assymetrical), I would think that it would effect the + and - signal
and conductors in a balanced cable equally.
The differential input would then eliminate most of the RFI since it
is common to both legs of the signal path.
Norman's point is that the balanced audio amplifiers are typically not
very effective in cancelling out common-mode signals at RF frequencies.
For example, if you have a common-mode signal in the + and the - paths
at 1 KHz, the amplifier may subtract it out very well. But if the signal
is at 100 MHz, the amplifier will not subtract it well at all.