[RFI] PME (Was: Earth isolation)

[Ian White, G3SEK]

George Shaw wrote:
>
>The original question was more to do with interference caused by a 
>nearby Tx antenna used by another radio operator (not a ham) getting to 
>my audio equipment which is connected to my TxRx. My own equipment is 
>near quiet as I have proven when the neighbour was not operating. I 
>suspect that my mains is picking up the Tx from next door, I was 
>thinking of a mains filter, what type, who makes them (240V-50Hz)
>
There are several different problems here.

First, what kind of "radio operator" do you have, next door? Licensed, 
or not? What frequency, what power?

Second, you say your own equipment is "near quiet"... so it's not 
totally immune to your own transmissions? Again, you need to give a lot 
more detail before anyone here can really help.



>Now another question. Any thoughts or comments/data on Protective 
>Multiple Earthing systems and interference or use near/in radio 
>installations?
>
For information, PME is a British system by which the electricity 
supplier takes over responsibility for safety grounding, by multiple 
grounding of the neutral supply line. The claimed advantage is that 
users don't have to rely on the quality of grounding at each individual 
house.

Inside the house, all accessible metalwork has to be bonded to the 
common earth bus, which is connected to the grounded neutral. This makes 
a safe "equipotential zone" inside the house... but it isn't necessarily 
the same potential is the ground on which the house is built. When you 
connect *anything* out of the house to the real world outside, the whole 
concept comes unglued.

 From the specific viewpoint of RFI, George and his "radio operator" 
neighbor may be sharing a common ground/neutral lead, which may go 
several yards back up the supply system before it finds an earth spike.

Personally I hate, loathe, detest and despise PME! If I ever move to a 
house that has PME (a distinct possibility in the next 12 months), the 
first thing I'll do is change it, and provide my own earth connection 
that is short and direct.

As far as I know, there is no objection to George installing a good 
ground of his own, with the shortest possible lead-in to the earth 
busbar in the "consumer unit" (breaker panel). That could be a big help 
with the RFI... but there are detailed regulations about the size of 
wire and earth spike required. Consult the 'IEE On-Site Guide.'



>Also anyone ever had a electricity supply board timer (used to change 
>for daytime high rate to evening/night time low rate) cause 
>interference to radio or telephone circuits by introducing a click, 
>click, click steady repeated sound?
>
Sorry, no info on that.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek