Freeview: Faint striations on image. Analogue: Faint ghosting

Hi

My old external TV aerial was broken and pointing at a "funny"
angle. I could receive BBC1, BBC2 and C5 plus UK History (!) but
nothing else through a Sony DX800 Freeview box. The TV image on the
"good" channels was just fine.

I have had a new external TV aerial plus an FM "omni" (circular)
aerial fitted externally on a new mast. I am assured well-screened
standard satellite coax (DG6?) was used for the TV signal. Problem is,
I get faint "striations" on the TV image through the Sony Freeview box
and slight ghosting when feeding the analog/RF signal from the aerial
directly into the TV. DVD sourced signals through SCART show no such
striations or ghosting on the TV. I thought the new TV signal might be
too strong but the Sony "support" screen indicates the signal quality
is good and strength is "average". The TV aerial is situated
externally on an chimney stack quite high up (ie not in a valley) in
Barnet Herts.

I have done some Googling but can't find what causes this striation
- any ideas?

FM quality is fine.


Regards


Clive

....snip...
The TV aerial is situated
externally on an chimney stack quite high up (ie not in a valley) in
Barnet Herts.


Where exactly in Barnet? Unlike Enfield, there are hills and troughs and
I've noticed aerials pointing all over the place ;-). BTW, does the new
aerial point in the same general direction, did you have ghosting before and
did you get a "digital" (i.e. wideband) aerial fitted?

If you were pointing at Crystal Palace then you should have had a group A
installed.

Paul DS

On Aug 3, 3:27 pm, "Paul D.Smith" wrote:
...snip...
The TV aerial is situated

externally on an chimney stack quite high up (ie not in a valley) in
Barnet Herts.

Where exactly in Barnet? Unlike Enfield, there are hills and troughs and
I've noticed aerials pointing all over the place ;-). BTW, does the new
aerial point in the same general direction, did you have ghosting before and
did you get a "digital" (i.e. wideband) aerial fitted?

If you were pointing at Crystal Palace then you should have had a group A
installed.

Paul DS

I'm in New Barnet, Victoria Road, EN4 down from the train station but
not in the valley before it climbs up to Cockfosters.

Previously I only fed the aerial lead into the Sony Freeview box. The
old aerial had no "reflector" at the back, used brown coax downlead,
terminated in a little junction box etc. etc. which all (as received
wisdom states) attentuate the signal. Previously I had had good BBC1,
BBC2, C5,History Channel and the usual useless bid-up, bid-down TV
channels - but no BBC4 - which is what I wanted. I never previously
tried the old aerial to provide an analog signal direct into the TV so
I don't known if there was ghosting on the analog image.

The visual effects of striations (digital) only occur on the
previously "good" channels (I think). Also these image "defects" are
slight but enough to be distracting when the image has large areas of
a single colour such as sky or grass in a field.

The new aerial is pointing in the same direction as the old one.

I had a look here

http://www.tellyaerial.34sp.com/ta.php/interference

but none of the images show exactly the problem I see . The problem I
see is a (little) bit like the "Adjecent (sic) channel" example but
the effect on mine is much less than that in the example shown. Also
"my" pattern is a very regular diagonol distortion - not the
"herringbone" effect .

A bit of Googling is suggesting (but maybe it's my diy-diagnosis) the
problem may be due to signal overload. £4.99 for a 6dB or 12dB
attentuator from Maplin in Turnpike Lane maybe worth a punt?

Thanks

Clive

I had a look here

http://www.tellyaerial.34sp.com/ta.php/interference

but none of the images show exactly the problem I see . The problem I
see is a (little) bit like the "Adjecent (sic) channel" example but
the effect on mine is much less than that in the example shown. Also
"my" pattern is a very regular diagonol distortion - not the
"herringbone" effect .

A bit of Googling is suggesting (but maybe it's my diy-diagnosis) the
problem may be due to signal overload. £4.99 for a 6dB or 12dB
attentuator from Maplin in Turnpike Lane maybe worth a punt?


Is it definitely not Tetra interference?

Has the lead been terminated in a wall plate, and if so, is it a good one
with a quality flylead to the receiver?

You can try an attenuator, but it shouldn't cause patterning on a digital
signal. How are you feeding the receiver to the TV - via Scart? If so, have
you tried another Scart lead?

Has it been there since the new aerial was installed? Did you mention it to
the rigger?

Pity about the circular FM aerial.

If you are getting striations on your picture when watching a signal from
your Freeview box, the problem is almost certainly SCART cross-talk.

What happens is the video output wire (from the TV) in the SCART lead
induces a faint signal on the video input wires in the same lead, causing
strange effects like these.

You can cure this by cutting the video output wire in the SCART socket,
although it then renders your SCART lead directional.

Alternatively you might try a more expensive (fully screened) SCART lead.

I am by NO means an expert, so hopefully someone else will chime in soon
with a more coherent answer!

Steve

In message , Steve Thackery
wrote


Alternatively you might try a more expensive (fully screened) SCART lead.

Fully screened ribbon cable SCART leads are around 2 quid from CPC -
hardly expensive.


--
Alan
news2006 {at} amac {dot} f2s {dot} com

On Aug 4, 12:03 am, "Steve Thackery" wrote:
If you are getting striations on your picture when watching a signal from
your Freeview box, the problem is almost certainly SCART cross-talk.

What happens is the video output wire (from the TV) in the SCART lead
induces a faint signal on the video input wires in the same lead, causing
strange effects like these.

You can cure this by cutting the video output wire in the SCART socket,
although it then renders your SCART lead directional.

Alternatively you might try a more expensive (fully screened) SCART lead.

I am by NO means an expert, so hopefully someone else will chime in soon
with a more coherent answer!

Steve

Hi

A couple of things to add to the mix.

All the devices (DVD player, DTT/DTV box and Archos AV500) connect to
the TV via a Scart switch box. This was the setup before the new
aerial and didn't result in the (faint) diagonal striations. I have
this setup so I don't have the AV500 powered all the time and I can
select the source (DTV or DVD) to record from.

This morning I connected an old VCR to the AV2 "phono plug" input at
the front of the TV i.e. bypassing the SCART switch. When I have the
aerial attached to the VCR I see the striations, when I detach the
aerial flylead from the VCR the striations disappear from the image.


Hmmmmm .....

More effects.

When I have the aerial attached to the DTV / Freeview device but the
SCART switched to display the DVD (VCR not attached), then I see the
vertical striations slightly inclined from bottom left to top right
(10 degress??). The striations are about 3mm in width and move across
the image from left to right and cover the screen width in about 8 to
10 seconds (counting in my head).

If I switch the SCART to display the DTV image when aerial is attached
I see these almost-vertical striations but superimposed are 45 degree
diagonal striations causing a strange shimmering (moire?) effect.

Removing the aerial from the DTV device and the striations disappear
immediately. If I bring the aerial plug very close to the aerial / RF
socket on the DTV device the striations start to reappear.

Regarding the circular FM aerial - these are much scorned on the Web
sites I have read. However, I think the reason they are fitted is they
are compact and easy to fit on a mast under the TV aerial rather than
a long, vertical FM dipole. The performance of FM for the stations I
want, is fine to my ears on my not very high hi-fi.

Thanks

Clive

Clive wrote:
More effects.

When I have the aerial attached to the DTV / Freeview device but the
SCART switched to display the DVD (VCR not attached), then I see the
vertical striations slightly inclined from bottom left to top right
(10 degress??). The striations are about 3mm in width and move across
the image from left to right and cover the screen width in about 8 to
10 seconds (counting in my head).

If I switch the SCART to display the DTV image when aerial is attached
I see these almost-vertical striations but superimposed are 45 degree
diagonal striations causing a strange shimmering (moire?) effect.

Removing the aerial from the DTV device and the striations disappear
immediately. If I bring the aerial plug very close to the aerial / RF
socket on the DTV device the striations start to reappear.

Regarding the circular FM aerial - these are much scorned on the Web
sites I have read. However, I think the reason they are fitted is they
are compact and easy to fit on a mast under the TV aerial rather than
a long, vertical FM dipole. The performance of FM for the stations I
want, is fine to my ears on my not very high hi-fi.

Thanks

Clive

It sounds to me like the aerial install is of insufficient quality, if the
installer didn't use CT100 or similar quality coax then that is very likely
to be the cause of your problem.

"I'm in New Barnet, Victoria Road, EN4 down from the train station but
not in the valley before it climbs up to Cockfosters."


-----------------------
could just be that you are next to a tv transmitter...

http://tx.mb21.co.uk/gallery/new-barnet.shtml

"Bit of an unusual one this, comprising a stack of four vertical bowtie
dipoles bolted to the top of the framework of a Gasometer, located next to
the Victoria Recreation Ground in New Barnet. The direction of transmission
is primarily to the south west of the site."

you might need filters to remove all but 'group A' signals
regards
gremlin

please reply to group.