[Malvern] Electrical Intreference

[Steve Cashmore]

Hi Ian,

Ian Pascoe wrote:
> For any sensitive electrical equipment it is generally recommended to have
> an RF filter somewhere on the mains feed to remove spikes that come in over
> the mains power.
> 
> If you are converting from AC to DC power will these spikes still be there
> after the conversion?
> 
> If you transform the power down from 240v AC to say 12v AC does the spikes
> decrease in line with the reduction or do they stay the same?

Unfortunately fast rise-time spikes tend to capacitively couple their 
energy directly to the output through components of the conversion 
circuitry such as a transformer.  For that reason it's hard to predict 
exactly what reduction there may be for a given circuit. It has much to 
do with the physical construction of transformers and assembly of the 
final product.

> And lastly, I have read that if a neighbour uses the mains ring to provide
> data transfer for either audio or computer networks, that extra information
> leaks back out into the mains distribution.  Would an RF filter remove it or
> do you need something else?

Yes, an RF filter will remove the data modulation from external 
radiation through the mains network.  Without such a filter, a reduced 
signal may be present up to the transformer sub-station.  There are such 
commercial domestic filters available although I can't point to a 
specific example.  Some clip-on across the incoming house wiring making 
no electrical connection, but have limited filtering, and others are 
physically wired at the distribution board and provide a high degree of 
isolation.

Schaffner are a well known manufacturer of filtering devices in Europe. 
  In the USA these RF filters are often available from whole house 
remote control equipment suppliers.  Many of these systems use a low 
frequency RF modulation on the house wiring for control purposes.

best regards,