Had a job recently where the house was near to a local TV transmitter.
I could not get a decent BER quality reading. Tried earthing the
dishe, that made no difference. Tried increasing the dish size, that
made things worse. Tried resiting the dish behind a building, that
helped a bit, but is still not perfect. Any sensible suggestions
welcomed on how I can help this customer?

TIA - Mark in Spain.

On Sat, 27 Aug 2011 11:32:08 +0100, "Anthony R. Gold"
wrote:

On Sat, 27 Aug 2011 11:25:23 +0200, Anti-Spam wrote:

Had a job recently where the house was near to a local TV transmitter.
I could not get a decent BER quality reading. Tried earthing the
dishe, that made no difference. Tried increasing the dish size, that
made things worse. Tried resiting the dish behind a building, that
helped a bit, but is still not perfect. Any sensible suggestions
welcomed on how I can help this customer?

I would expect the signals are being picked up by downleads and if so then
the location of the dish would be immaterial. You may need low pass filters
ahead of the receiver or notched ones tuned to the problem TV channels.

Try an attenuator - it's a cheap and easy test and you probably have some in
your tool kit already. But if that does not help then determine the channel
frequencies coming from the TV mast then ask these folks (or someone similar)
if they can supply something suitable: http://www.taylorbros.co.uk/. If you
have a local supplier you may be able to do your testing before buying
anything.

How about deliberate earthing of both ends (or start with the receiver
end) of the co-ax ? If you earth only the dish you are IIRC generally
leaving the receiver floating on the other end of the cable.

On Sun, 28 Aug 2011 04:05:58 +0100, Charles Ellson
wrote:

On Sat, 27 Aug 2011 11:32:08 +0100, "Anthony R. Gold"
wrote:

On Sat, 27 Aug 2011 11:25:23 +0200, Anti-Spam wrote:

Had a job recently where the house was near to a local TV transmitter.
I could not get a decent BER quality reading. Tried earthing the
dishe, that made no difference. Tried increasing the dish size, that
made things worse. Tried resiting the dish behind a building, that
helped a bit, but is still not perfect. Any sensible suggestions
welcomed on how I can help this customer?

I would expect the signals are being picked up by downleads and if so then
the location of the dish would be immaterial. You may need low pass filters
ahead of the receiver or notched ones tuned to the problem TV channels.

Try an attenuator - it's a cheap and easy test and you probably have some in
your tool kit already. But if that does not help then determine the channel
frequencies coming from the TV mast then ask these folks (or someone similar)
if they can supply something suitable: http://www.taylorbros.co.uk/. If you
have a local supplier you may be able to do your testing before buying
anything.

How about deliberate earthing of both ends (or start with the receiver
end) of the co-ax ? If you earth only the dish you are IIRC generally
leaving the receiver floating on the other end of the cable.

I did not earth the downlead, just the metal work of the dish. I had
assumed that because increasing the dish size made things worse, that
it was the dish acting as a TV antenna that was the problem. Will do a
return visit to the customer, and try earthing the downlead (both ends
if need be). Thanks.

PS what does IIRC mean?

"Anti-Spam" wrote in message
...
On Sun, 28 Aug 2011 04:05:58 +0100, Charles Ellson
wrote:

On Sat, 27 Aug 2011 11:32:08 +0100, "Anthony R. Gold"
wrote:

On Sat, 27 Aug 2011 11:25:23 +0200, Anti-Spam
wrote:

Had a job recently where the house was near to a local TV
transmitter.
I could not get a decent BER quality reading. Tried earthing
the
dishe, that made no difference. Tried increasing the dish
size, that
made things worse. Tried resiting the dish behind a
building, that
helped a bit, but is still not perfect. Any sensible
suggestions
welcomed on how I can help this customer?

I would expect the signals are being picked up by downleads
and if so then
the location of the dish would be immaterial. You may need low
pass filters
ahead of the receiver or notched ones tuned to the problem TV
channels.

Try an attenuator - it's a cheap and easy test and you
probably have some in
your tool kit already. But if that does not help then
determine the channel
frequencies coming from the TV mast then ask these folks (or
someone similar)
if they can supply something suitable:
http://www.taylorbros.co.uk/. If you
have a local supplier you may be able to do your testing
before buying
anything.

How about deliberate earthing of both ends (or start with the
receiver
end) of the co-ax ? If you earth only the dish you are IIRC
generally
leaving the receiver floating on the other end of the cable.

I did not earth the downlead, just the metal work of the dish.
I had
assumed that because increasing the dish size made things
worse, that
it was the dish acting as a TV antenna that was the problem.
Will do a
return visit to the customer, and try earthing the downlead
(both ends
if need be). Thanks.

PS what does IIRC mean?



If I remember correctly

On 28/08/2011 12:54, Anthony R. Gold wrote:
On Sun, 28 Aug 2011 04:05:58 +0100, Charles Ellson
wrote:

On Sat, 27 Aug 2011 11:32:08 +0100, "Anthony R. Gold"
wrote:

On Sat, 27 Aug 2011 11:25:23 +0200, wrote:

Had a job recently where the house was near to a local TV transmitter.
I could not get a decent BER quality reading. Tried earthing the
dishe, that made no difference. Tried increasing the dish size, that
made things worse. Tried resiting the dish behind a building, that
helped a bit, but is still not perfect. Any sensible suggestions
welcomed on how I can help this customer?

I would expect the signals are being picked up by downleads and if so then
the location of the dish would be immaterial. You may need low pass filters
ahead of the receiver or notched ones tuned to the problem TV channels.

Try an attenuator - it's a cheap and easy test and you probably have some in
your tool kit already. But if that does not help then determine the channel
frequencies coming from the TV mast then ask these folks (or someone similar)
if they can supply something suitable: http://www.taylorbros.co.uk/. If you
have a local supplier you may be able to do your testing before buying
anything.

How about deliberate earthing of both ends (or start with the receiver
end) of the co-ax ? If you earth only the dish you are IIRC generally
leaving the receiver floating on the other end of the cable.

This ain't power or audio, it's RF. If the TV transmission is at say 600 MHz
(Spanish Channel 37) the wavelength is 0.5 metres, so earth one point on the
line and it will be hot again 25 cm (a half wavelength) away from that point.

I mentioned earthing at both ends not at some random single point along
the braid. It should cost next to nothing to do it so there is no harm
in trying.

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

I mentioned earthing at both ends not at some random single point
along the braid. It should cost next to nothing to do it so there
is no harm in trying.

RF Earth Loops are A Bad Thing...

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

On Mon, 29 Aug 2011 11:15 +0100 (BST), (Paul
Cummins) wrote:

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

I mentioned earthing at both ends not at some random single point
along the braid. It should cost next to nothing to do it so there
is no harm in trying.

RF Earth Loops are A Bad Thing...

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.

On Mon, 29 Aug 2011 11:26:27 +0100, "Anthony R. Gold"
wrote:

On Mon, 29 Aug 2011 01:18:02 +0100, Charles Ellson
wrote:

On 28/08/2011 12:54, Anthony R. Gold wrote:
On Sun, 28 Aug 2011 04:05:58 +0100, Charles Ellson
wrote:

On Sat, 27 Aug 2011 11:32:08 +0100, "Anthony R. Gold"
wrote:

On Sat, 27 Aug 2011 11:25:23 +0200, wrote:

Had a job recently where the house was near to a local TV transmitter.
I could not get a decent BER quality reading. Tried earthing the
dishe, that made no difference. Tried increasing the dish size, that
made things worse. Tried resiting the dish behind a building, that
helped a bit, but is still not perfect. Any sensible suggestions
welcomed on how I can help this customer?

I would expect the signals are being picked up by downleads and if so then
the location of the dish would be immaterial. You may need low pass filters
ahead of the receiver or notched ones tuned to the problem TV channels.

Try an attenuator - it's a cheap and easy test and you probably have some in
your tool kit already. But if that does not help then determine the channel
frequencies coming from the TV mast then ask these folks (or someone similar)
if they can supply something suitable: http://www.taylorbros.co.uk/. If you
have a local supplier you may be able to do your testing before buying
anything.

How about deliberate earthing of both ends (or start with the receiver
end) of the co-ax ? If you earth only the dish you are IIRC generally
leaving the receiver floating on the other end of the cable.

This ain't power or audio, it's RF. If the TV transmission is at say 600 MHz
(Spanish Channel 37) the wavelength is 0.5 metres, so earth one point on the
line and it will be hot again 25 cm (a half wavelength) away from that point.

I mentioned earthing at both ends not at some random single point along
the braid. It should cost next to nothing to do it so there is no harm
in trying.

The very concept of "earthing" makes no sense at RF.

ISTR transmitting aerial engineers might disagree.

You can bond various
things together but, in general, none of them will be at "earth" and nor will
the various bonding places be at equi-potential. If the choice is based on
anything that is harmless regardless of a technical basis then prayer and
shouting have the advantage of not needing a ladder to reach the dish :-)

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.

RF should be earthed only at one point, and earthing the dish itself is
utterly pointless as it's only a mirror.

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

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.

None of these are linked to Mains "Earth" in any way, and none can fault
to Mains live.

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