Interference from TV transmitter

**Charles Ellson** · #11 August 30th 11, 03:20 AM posted to uk.tech.tv.sky

On Tue, 30 Aug 2011 01:29 +0100 (BST), lid
(Paul Cummins) wrote:

We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

When something flows around them. OTOH earthing/EPBing something
that
might be acting as an aerial is in with a chance of being a good
thing.

If an Earth Loop creates a resonant lop at a frequency you don't want to
get into your equipment, an Earth Loop on RF shield is a VERY Bad Thing.

Especially when you consider that an Earth Loop of this ilk will
effectively be creating a delta-matched Terminated Dipole, which is a
very good aerial in general terms, on a frequency you can;t calculate or
control.

A bit like the inverted L aerial of no specific dimensions (meant for
MW reception) which I accidentally found some years ago worked rather
well around 100MHz.

RF should be earthed only at one point,

Agreed as an ideal but the ideal is not always necessary (if e.g. just
earthing the receiver cures it, something that can usually be tried
with two croc clips and a bit of wire).

and earthing the dish itself is
utterly pointless as it's only a mirror.

Indeed, it is the braid/screen of the co-ax which needs the
connection. I think you're the first to spot that error WRT to the
dish end of the lead.

**Charles Ellson** · #12 August 30th 11, 03:48 AM posted to uk.tech.tv.sky

On Tue, 30 Aug 2011 01:29 +0100 (BST), lid
(Paul Cummins) wrote:

We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

ISTR transmitting aerial engineers might disagree.

The "earth" for RF purposes is a reflection of the antenna.

Common antennas used for Transmitting have no RF earth, such as the
Dipole, Looped Dipole and Terminated Dipole.

Others, normally Monopole types, do have an "earth" but only to create an
electrical reflaction of the monopole, such as in a Quarter-wave used on
a car or similar.

Half-wave monopoles often have no earthing at all.

If you must have a connection to actual Earth, it should be as close to
the TRX as possible, and as direct as possible. As an example, have an
RF earth bond linking my Sky feeder, my TV feeder, my DAB feeder, my YHF
feeder and my HF feeder all bonded to a wide strip of copper as close to
the house Antnenna entry points as possible, then bonded via a 3mm earch
cable to a single copper pipe buried into the earth outside my door.
Single earth, no loops.

Nice.

None of these are linked to Mains "Earth" in any way,

Which ISTR might become evident in very dry weather if you put one
hand on any metalwork connected to your local earth and the other on
something connected to mains earth such as a metal-cased fan.

and none can fault to Mains live.

**Paul Cummins[_2_]** · #13 August 30th 11, 11:06 AM posted to uk.tech.tv.sky

We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

something connected to mains earth such as a metal-cased fan.

Nothing that I can touch while using the RF equipment has any direct
connection to Mains Earth. All of the RF equipment is either
double-insulated or run from 13.8v supplies.

And in any case, the Copper pipe is deep enough in that it crosses the
water table.

--
Paul Cummins - Always a NetHead
Wasting Bandwidth since 1981

**Charles Ellson** · #14 August 30th 11, 09:49 PM posted to uk.tech.tv.sky

On 30/08/2011 12:06, Paul Cummins wrote:
We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

something connected to mains earth such as a metal-cased fan.

Nothing that I can touch while using the RF equipment has any direct
connection to Mains Earth. All of the RF equipment is either
double-insulated or run from 13.8v supplies.

So, no socket outlets in the same room ?

And in any case, the Copper pipe is deep enough in that it crosses the
water table.

**Paul Cummins[_2_]** · #15 August 31st 11, 12:49 AM posted to uk.tech.tv.sky

We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

Nothing that I can touch while using the RF equipment has any
direct
connection to Mains Earth. All of the RF equipment is either
double-insulated or run from 13.8v supplies.

So, no socket outlets in the same room ?

In the same room, but not within reach of the Earth Strip.

--
Paul Cummins - Always a NetHead
Wasting Bandwidth since 1981

**Charles Ellson** · #16 August 31st 11, 01:40 AM posted to uk.tech.tv.sky

On Wed, 31 Aug 2011 01:49 +0100 (BST), lid
(Paul Cummins) wrote:

We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

Nothing that I can touch while using the RF equipment has any
direct
connection to Mains Earth. All of the RF equipment is either
double-insulated or run from 13.8v supplies.

So, no socket outlets in the same room ?

In the same room, but not within reach of the Earth Strip.

IMU that is still "naughty" as it does not prevent someone else in the
room plugging in something with an earthed case and putting it within
touching distance (with the apparent presumption that no-one would
plug in something with a long lead outside the room and bring it in).
What does seem to be OK if I've correctly interpreted various
interpretations of the current wiring regs is to feed L+N only to the
room via an RCD and use only your local earth as a protective earth
within the room; I had to do this some time ago with a parked railway
carriage for vaguely similar reasons (i.e. no bonding between the
incoming earth and the vehicle/track as it had to be moveable without
notice).

**Paul Cummins[_2_]** · #17 August 31st 11, 11:42 AM posted to uk.tech.tv.sky

We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

What does seem to be OK if I've correctly interpreted various
interpretations of the current wiring regs is to feed L+N only to
the room via an RCD and use only your local earth as a protective earth
within the room;

fx: looks around

Nothing in the room has an Earth wire, it's all Double Insulated stuff...
So while there is Earth on the sockets, nothing in the room is positively
earthed via the sockets, and the ring is RCCD protected.

So I'm nearly there...

IMU that is still "naughty" as it does not prevent someone else in
the room plugging in something with an earthed case and putting it
within touching distance

Only me living here...

--
Paul Cummins - Always a NetHead
Wasting Bandwidth since 1981

**Charles Ellson** · #18 August 31st 11, 11:36 PM posted to uk.tech.tv.sky

On Wed, 31 Aug 2011 12:42 +0100 (BST), lid
(Paul Cummins) wrote:

We were about to embark at Dover, when
(Charles Ellson) came up to me and whispered:

What does seem to be OK if I've correctly interpreted various
interpretations of the current wiring regs is to feed L+N only to
the room via an RCD and use only your local earth as a protective earth
within the room;

fx: looks around

Nothing in the room has an Earth wire, it's all Double Insulated stuff...
So while there is Earth on the sockets, nothing in the room is positively
earthed via the sockets, and the ring is RCCD protected.

So I'm nearly there...

IMU that is still "naughty" as it does not prevent someone else in
the room plugging in something with an earthed case and putting it
within touching distance

Only me living here...

Same here now but what spoils it is the almost inevitable need for
someone else to fix something at some time and find some way of
enabling any latent hazard. About 30 years ago there were a couple of
dozen circuits blown in Hampstead telephone exchange; the fault was
traced to an office a mile away in Hampstead High Street where a
workman had plugged in a defective electric drill which had a live to
earth fault, the earth wiring in the office was incomplete but was
connected between the relevant socket outlet and the SO which the
telephone system was plugged into. Unfortunately the person who
installed that system had failed to provide the specified
signalling/protective earth between the power unit and the building
main earth (that earth being strapped to the plug-in earth in the
power unit) so the mains current's only escape was down the telephone
lines via the telephone system at the times that an earth signalling
path existed (fortunately for the man with the dud drill there was
practically no exposed metalwork where he was working).

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