Terrestrial DTV in the UK - Channel offsets

Hi All,

Can anyone tell me what offsets are being used on each of the digital
multiplexes from Crystal Palace ?

I can't believe how difficult it is to find this information, so any
links would be great.

Thanks in advance,

UKM

wrote:
Hi All,

Can anyone tell me what offsets are being used on each of the digital
multiplexes from Crystal Palace ?

I can't believe how difficult it is to find this information, so any
links would be great.

http://www.ofcom.org.uk/static/reception_advice/digital_trans_guide/show_transmitter.asp-siteID=66.html

On Jun 20, 9:04*am, Mark Carver wrote:
wrote:
Hi All,

Can anyone tell me what offsets are being used on each of the digital
multiplexes from Crystal Palace ?

I can't believe how difficult it is to find this information, so any
links would be great.

http://www.ofcom.org.uk/static/reception_advice/digital_trans_guide/s...

Great,

Thanks for this Mark. I looked on there before, so why is their seach
enginge so pants ?

UKM

wrote:
On Jun 20, 9:04 am, Mark Carver wrote:
wrote:
Hi All,
Can anyone tell me what offsets are being used on each of the digital
multiplexes from Crystal Palace ?
I can't believe how difficult it is to find this information, so any
links would be great.
http://www.ofcom.org.uk/static/reception_advice/digital_trans_guide/s...

Great,

Thanks for this Mark. I looked on there before, so why is their seach
enginge so pants ?

Considering who they are, you're right, their website is a mess.

--
Mark
Please replace invalid and invalid with gmx and net to reply.

On Fri, 20 Jun 2008 09:04:14 +0100, Mark Carver
wrote:

wrote:
Hi All,

Can anyone tell me what offsets are being used on each of the digital
multiplexes from Crystal Palace ?

I can't believe how difficult it is to find this information, so any
links would be great.

http://www.ofcom.org.uk/static/reception_advice/digital_trans_guide/show_transmitter.asp-siteID=66.html

Just as a matter of interest, why is the channel offset by 167 kHz
anyway and why only one out of six?

On 20/06/2008 20:24, Scott wrote:

Mark Carver wrote:

http://www.ofcom.org.uk/static/reception_advice/digital_trans_guide/show_transmitter.asp-siteID=66.html

Just as a matter of interest, why is the channel offset by 167 kHz
anyway and why only one out of six?

From Crystal Palace, five muxes have negative offset, one has positive
offset, none have zero. It's different from other transmitters, e.g.
Waltham has all zero

http://www.ofcom.org.uk/static/recep...siteID=60.html

On Fri, 20 Jun 2008 22:42:12 +0100, Andy Burns
wrote:

On 20/06/2008 20:24, Scott wrote:

Mark Carver wrote:

http://www.ofcom.org.uk/static/reception_advice/digital_trans_guide/show_transmitter.asp-siteID=66.html

Just as a matter of interest, why is the channel offset by 167 kHz
anyway and why only one out of six?

From Crystal Palace, five muxes have negative offset, one has positive
offset, none have zero. It's different from other transmitters, e.g.
Waltham has all zero

http://www.ofcom.org.uk/static/recep...siteID=60.html

I see. I missed the - sign. Still don't know what offset is or does.

Scott wrote:
On Fri, 20 Jun 2008 22:42:12 +0100, Andy Burns
wrote:

On 20/06/2008 20:24, Scott wrote:

Mark Carver wrote:

http://www.ofcom.org.uk/static/reception_advice/digital_trans_guide/show_transmitter.asp-siteID=66.html
Just as a matter of interest, why is the channel offset by 167 kHz
anyway and why only one out of six?
From Crystal Palace, five muxes have negative offset, one has positive
offset, none have zero. It's different from other transmitters, e.g.
Waltham has all zero

http://www.ofcom.org.uk/static/recep...siteID=60.html

I see. I missed the - sign. Still don't know what offset is or does.

The offset is if the digital carrier is adjacent to an analogue channel.
If the digital carrier is the channel below the analogue then the offset
is -167kHz but if the digital carrier is above the analogue then the
offset is +167.

It's to stop the analogue carrier from interfering with the Digital
carrier. Might also be to do with the stability of the output frequency
of the analogue transmitter and tolerances of the same.

This why modulators in sky boxes and VCR's etc shouldn't be tuned to a
channel next to a digital carrier. It can cause breakup on DTT.

Glenn...

Glenn Millar wrote:

Scott wrote:
I see. I missed the - sign. Still don't know what offset is or does.

It's just an offset of the centre frequency of the digital transmission
above or below the centre frequency of the TV channel. For example a
DTT transmission on UHF channel 21 with zero offset would be centred on
474.000 MHz (±500 Hz). With a positive offset the signal would be
centred on 474.167 MHz. Where used, the offset is always 1/6 of a MHz,
so is described completely by a single character (-, + or 0).

The offset is if the digital carrier is adjacent to an analogue channel.
If the digital carrier is the channel below the analogue then the offset
is -167kHz but if the digital carrier is above the analogue then the
offset is +167.

Except that -ve offsets are never used on ch. 21, nor +ve offsets on ch.
68. There are strict out-of-band spectrum masks to meet.

It's to stop the analogue carrier from interfering with the Digital
carrier.

That's a bit vague. DTT offsets are used to ease the filtering
requirements at transmitter outputs where there is adjacent channel
working with analogue and where shared transmitting aerials are used.

Might also be to do with the stability of the output frequency
of the analogue transmitter and tolerances of the same.

Well analogue uses offsets too, to reduce the visibility of co-channel
interference. Here the offset value is smaller, viz. 5/3 times line
scan rate (~21 kHz). With an analogue transmission with +ve offset on
channel N there'd be almost zero space between the upper edge of the
NICAM component of the analogue signal and the lowest COFDM carrier of a
DTT signal on channel N+1, unless the DTT is offset upwards.

This why modulators in sky boxes and VCR's etc shouldn't be tuned to a
channel next to a digital carrier. It can cause breakup on DTT.

These modulators are double-sideband, so you obviously don't want one
N+1 relative to DTT, but I don't see why N-1 would be a problem. The
main thing is to ensure the modulator's not co-channel with any DTT,
otherwise your distributed Sky RF-2 signal will look a bit noisy. . .

--
Andy

On Sat, 21 Jun 2008 23:13:03 +0100, Andy Wade
wrote:

Glenn Millar wrote:

Scott wrote:
I see. I missed the - sign. Still don't know what offset is or does.

It's just an offset of the centre frequency of the digital transmission
above or below the centre frequency of the TV channel. For example a
DTT transmission on UHF channel 21 with zero offset would be centred on
474.000 MHz (±500 Hz). With a positive offset the signal would be
centred on 474.167 MHz. Where used, the offset is always 1/6 of a MHz,
so is described completely by a single character (-, + or 0).

The offset is if the digital carrier is adjacent to an analogue channel.
If the digital carrier is the channel below the analogue then the offset
is -167kHz but if the digital carrier is above the analogue then the
offset is +167.

Except that -ve offsets are never used on ch. 21, nor +ve offsets on ch.
68. There are strict out-of-band spectrum masks to meet.

It's to stop the analogue carrier from interfering with the Digital
carrier.

That's a bit vague. DTT offsets are used to ease the filtering
requirements at transmitter outputs where there is adjacent channel
working with analogue and where shared transmitting aerials are used.

Might also be to do with the stability of the output frequency
of the analogue transmitter and tolerances of the same.

Well analogue uses offsets too, to reduce the visibility of co-channel
interference. Here the offset value is smaller, viz. 5/3 times line
scan rate (~21 kHz). With an analogue transmission with +ve offset on
channel N there'd be almost zero space between the upper edge of the
NICAM component of the analogue signal and the lowest COFDM carrier of a
DTT signal on channel N+1, unless the DTT is offset upwards.

This why modulators in sky boxes and VCR's etc shouldn't be tuned to a
channel next to a digital carrier. It can cause breakup on DTT.

These modulators are double-sideband, so you obviously don't want one
N+1 relative to DTT, but I don't see why N-1 would be a problem. The
main thing is to ensure the modulator's not co-channel with any DTT,
otherwise your distributed Sky RF-2 signal will look a bit noisy. . .

Does this mean they will end with analogue switch-off? Will the
decoders in affected areas need a rescan even if the channel numbers
on paper remain the same?