FW: FW: [Malvern] Electrical Intreference

[Ian Pascoe]

Hi Steve

Well you kinda got the reasoning right!

My brother got strange interference on his TV and Hi-fi but at only certain
times of the day.

A neighbour down the street who definately falls into the boys for toys
bracket has recently had one of these multi room hifi's using mains cable
for distribution installed.

He got himself an RF mains filter  and everything was hunky dory, but the
people in the flat above started to experience the same thing, so he asked
me and the rest is as they say history!

Mind you one other thought that comes to mind, that is does an RF filter
work both ways?

So let's assume I have more money than sense and install one of these mains
distributed systems, if I placed an in line filter between the meter and
fuse board would it stop the RF going in both directions or only one?  Or
put another way does it stop dead RF traffic in eithre direction once
installed?

Cheers

Ian

-----Original Message-----
From: malvern-bounces at mailman.lug.org.uk
[mailto:malvern-bounces at mailman.lug.org.uk]On Behalf Of Steve Cashmore
Sent: 28 January 2007 18:20
To: Malvern at mailman.lug.org.uk
Subject: Re: FW: [Malvern] Electrical Intreference


Well the main purpose of any RF mains filtering before say a Hi-Fi
amplifier is to reduce the effects of in-house equipment such as
refrigerators etc from inducing clicks and pops into the audio chain.
These are for mains conducted rather than radiated RF noise sources.
Such noise is naturally diminished by distance so typically, but by no
means always, such noise is greater from locally generated events.

One hopes that wireless induced noise would be naturally inhibited by
good circuit design/bandwidth control and layout within the Hi-Fi
equipment.  Sadly not always the case!

As to whether equipment SHOULD have such external filtering, then that
is another question.  I would say only if you have a problem.  I
understood your question was about preventing snooping on data
deliberately induced onto mains wiring for communication purposes.

Common filtered extension sockets are mainly just transient suppressing
devices designed to prevent damaging voltage spikes from destroying
semiconductor devices in the protected device.  Most non-rural locations
in the UK seem to enjoy a pretty good standard of clean electrical
supply compared to say the USA, and improved PSU design practice have
reduced the need for such devices IMHO.

that's enough rambling...
--
Steve

Ian Pascoe wrote:
> Hi Steve
>
> OK, that all makes sense.
>
> Rather intrigued about the in line filtering before the distribution panel
> in your home.
>
> If one of these were in place, would it be safe to presume that the amount
> of RF captured by induction within the house is neglible or should things
> like PCs audio systems etc still have their own RF filtering?


> Ian
>
> -----Original Message-----
> From: malvern-bounces at mailman.lug.org.uk
> [mailto:malvern-bounces at mailman.lug.org.uk]On Behalf Of Steve Cashmore
> Sent: 28 January 2007 14:23
> To: Malvern at mailman.lug.org.uk
> Subject: Re: [Malvern] Electrical Intreference
>
>
> 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,



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