COM 7-8 signal quality

[Bob Latham]

I have been receiving com7/com8 *mostly* from Sutton C for a couple
of years and apart from when I had a distribution amp failure, the
quality has been 100%.

Last week just by chance, I looked at the quality of com7 on a 10
year old Sony tv. I had a perfect picture and sound but the set said
the quality was zero. I had a quick check around our various TVs, the
old sets all gave excellent pictures but zero quality. Newer sets all
said the quality was 100%.

I grabbed my cheapo meter/analyser and shot up the loft where I can
get the feed directly from my aerial with only about 2M of cable.

Meter said:

COM7 CN 15% MER 19%
COM8 CN 77% MER 99%

Can't say exactly when this changed from the previous 'perfect' but
it was fine before christmas.

Is it reasonable to assume this is the SFN and another transmitter
damaging my signal?

Odd that all tvs show no sign of a problem with picture or sound and
that the new TVs tell the quality is 100%.

Bob.

[Mark Carver]

Post by Bob Latham
I have been receiving com7/com8 *mostly* from Sutton C for a couple
of years and apart from when I had a distribution amp failure, the
quality has been 100%.
Last week just by chance, I looked at the quality of com7 on a 10
year old Sony tv. I had a perfect picture and sound but the set said
the quality was zero. I had a quick check around our various TVs, the
old sets all gave excellent pictures but zero quality. Newer sets all
said the quality was 100%.
I grabbed my cheapo meter/analyser and shot up the loft where I can
get the feed directly from my aerial with only about 2M of cable.
COM7 CN 15% MER 19%
COM8 CN 77% MER 99%
Can't say exactly when this changed from the previous 'perfect' but
it was fine before christmas.
Is it reasonable to assume this is the SFN and another transmitter
damaging my signal?
Odd that all tvs show no sign of a problem with picture or sound and
that the new TVs tell the quality is 100%.

COM 8 switched to FEC 1/2 on February 10th, and reduced the bandwidth it
consumes from 8 MHz to 7 MHz.
COM 7 is still on 2/3 and 8 MHz, so that will explain the better
performance you've observed on COM 8 (Probably !)

[Bob Latham]

Post by Mark Carver
COM 8 switched to FEC 1/2 on February 10th, and reduced the
bandwidth it consumes from 8 MHz to 7 MHz. COM 7 is still on 2/3
and 8 MHz, so that will explain the better performance you've
observed on COM 8 (Probably !)

Very interesting, I don't doubt for a moment what you say but nothing
I have reveals any of this and in fact all TVs and my analyser insist
both com7 and 8 are still 8Mhz. They don't show FEC.

Thanks for the info.

Bob.

--
Bob Latham
Stourbridge, West Midlands

[Mark Carver]

Post by Bob Latham

Post by Mark Carver
COM 8 switched to FEC 1/2 on February 10th, and reduced the
bandwidth it consumes from 8 MHz to 7 MHz. COM 7 is still on 2/3
and 8 MHz, so that will explain the better performance you've
observed on COM 8 (Probably !)

Very interesting, I don't doubt for a moment what you say but nothing
I have reveals any of this and in fact all TVs and my analyser insist
both com7 and 8 are still 8Mhz. They don't show FEC.

Does COM 8 look the same width on screen as COM 7 (and the other muxes) ?
Bill Wright of this parish sent me a picture that shows it looking
narrower, but not as much as 1 MHz narrower.
I can't really tell on mine.

The reason for the trim, is that the guard band 55/56 fit into is only
15 MHz wide, and Arqiva have to comply
with that once the 700 MHz band becomes, 'Telco' property, in a month or
two.

[NY]

The reason for the trim, is that the guard band 55/56 fit into is only 15
MHz wide, and Arqiva have to comply
with that once the 700 MHz band becomes, 'Telco' property, in a month or
two.

Ah, so UHF 55/56 will be a protected band, even after the rest of the
spectrum above 700 MHz is sold off? I wasn't sure what was happening with
PSB7 and 8, and whether the sell-off was delayed until the demise of those
multiplexes.

How are all the rules about which frequencies a phone can transmit on in a
given country enforced (in the technical, not legal, sense)? In other words,
how does an existing phone "know" that as of a certain date it can use
frequencies above 700 MHz but not UHF 55/56, when previously it couldn't use
those frequencies? Or are these frequencies only used for the transmission
from the masts, and not for the reply from everyone's phones?

[Robin]

Post by Mark Carver

Post by Bob Latham

Post by Mark Carver
COM 8 switched to FEC 1/2 on February 10th, and reduced the
bandwidth it consumes from 8 MHz to 7 MHz. COM 7 is still on 2/3
and 8 MHz, so that will explain the better performance you've
observed on COM 8 (Probably !)

Very interesting, I don't doubt for a moment what you say but nothing
I have reveals any of this and in fact all TVs and my analyser insist
both com7 and 8 are still 8Mhz. They don't show FEC.

Does COM 8 look the same width on screen as COM 7 (and the other muxes) ?
Bill Wright of this parish sent me a picture that shows it looking
narrower, but not as much as 1 MHz narrower.
I can't really tell on mine.
The reason for the trim, is that the guard band 55/56 fit into is only
15 MHz wide, and Arqiva have to comply
with that once the 700 MHz band becomes, 'Telco' property, in a month or
two.

Less a data point, more evidence that I'm outside my comfort zone (think
a slug crossing a salt flat) but if I set VLC to capture from 754 MHz
with 7 MHz bandwidth I get nothing; with 8 MHz I get the expected
programmes.

Idiot boy question: is the nominal bandwidth necessarily the same as the
actual bandwidth used??

[Mark Carver]

Post by Robin

Post by Mark Carver

Post by Bob Latham

Post by Mark Carver
COM 8 switched to FEC 1/2 on February 10th, and reduced the
bandwidth it consumes from 8 MHz to 7 MHz. COM 7 is still on 2/3
and 8 MHz, so that will explain the better performance you've
observed on COM 8 (Probably !)

Very interesting, I don't doubt for a moment what you say but nothing
I have reveals any of this and in fact all TVs and my analyser insist
both com7 and 8 are still 8Mhz. They don't show FEC.

Does COM 8 look the same width on screen as COM 7 (and the other muxes) ?
Bill Wright of this parish sent me a picture that shows it looking
narrower, but not as much as 1 MHz narrower.
I can't really tell on mine.
The reason for the trim, is that the guard band 55/56 fit into is
only 15 MHz wide, and Arqiva have to comply
with that once the 700 MHz band becomes, 'Telco' property, in a month
or two.

Less a data point, more evidence that I'm outside my comfort zone
(think a slug crossing a salt flat) but if I set VLC to capture from
754 MHz with 7 MHz bandwidth I get nothing; with 8 MHz I get the
expected programmes.
Idiot boy question: is the nominal bandwidth necessarily the same as
the actual bandwidth used??

I believe it's all a bodge, the tx is flagged as an 8 MHz 'standard',
but just the lump of COFDM is only 7 MHz wide.

[Robin]

Post by Mark Carver

Post by Robin

Post by Mark Carver

Post by Bob Latham

Post by Mark Carver
COM 8 switched to FEC 1/2 on February 10th, and reduced the
bandwidth it consumes from 8 MHz to 7 MHz. COM 7 is still on 2/3
and 8 MHz, so that will explain the better performance you've
observed on COM 8 (Probably !)

Very interesting, I don't doubt for a moment what you say but nothing
I have reveals any of this and in fact all TVs and my analyser insist
both com7 and 8 are still 8Mhz. They don't show FEC.

Does COM 8 look the same width on screen as COM 7 (and the other muxes) ?
Bill Wright of this parish sent me a picture that shows it looking
narrower, but not as much as 1 MHz narrower.
I can't really tell on mine.
The reason for the trim, is that the guard band 55/56 fit into is
only 15 MHz wide, and Arqiva have to comply
with that once the 700 MHz band becomes, 'Telco' property, in a month
or two.

Less a data point, more evidence that I'm outside my comfort zone
(think a slug crossing a salt flat) but if I set VLC to capture from
754 MHz with 7 MHz bandwidth I get nothing; with 8 MHz I get the
expected programmes.
Idiot boy question: is the nominal bandwidth necessarily the same as
the actual bandwidth used??

I believe it's all a bodge, the tx is flagged as an 8 MHz 'standard',
but just the lump of COFDM is only 7 MHz wide.

Ta - nicely calibrated "teeny words for tiny tot" :)

[Andy Burns]

the guard band 55/56 fit into is only 15 MHz wide, and Arqiva have to
comply with that once the 700 MHz band becomes, 'Telco' property, in
a month or two.

Didn't think they'd even auctioned it yet?

[Mark Carver]

Post by Andy Burns

the guard band 55/56 fit into is only 15 MHz wide, and Arqiva have to
comply with that once the 700 MHz band becomes, 'Telco' property, in
a month or two.

Didn't think they'd even auctioned it yet?

Well, no, but I think it ceases to be the 'property' of broadcasters
regardless, and of course
we still have to comply for sake of the (geographical) neighbours.

[Bob Latham]

Post by Mark Carver
Does COM 8 look the same width on screen as COM 7 (and the other
muxes) ? Bill Wright of this parish sent me a picture that shows it
looking narrower, but not as much as 1 MHz narrower. I can't really
tell on mine.

My very cheapo analyser has a normal mode which shoes levels for each
channel but you can't see detail like shape or width. Here are two
pictures of the analyser in zoom mode which i suppose is intended to
show more detail but to be honest... I suppose you get what you pay
for. mine is a hobbyists toy really.

Loading Image...
Loading Image...

The only difference is where the frequency marker vertical bar is,
the first is C55 and the second C56. Interesting that there is
something on C57.

Bob.

[charles]

Post by Bob Latham

Post by Mark Carver
Does COM 8 look the same width on screen as COM 7 (and the other
muxes) ? Bill Wright of this parish sent me a picture that shows it
looking narrower, but not as much as 1 MHz narrower. I can't really
tell on mine.

My very cheapo analyser has a normal mode which shoes levels for each
channel but you can't see detail like shape or width. Here are two
pictures of the analyser in zoom mode which i suppose is intended to
show more detail but to be honest... I suppose you get what you pay
for. mine is a hobbyists toy really.
http://www.mightyoak.org.uk/tv/com7-8a.jpg
http://www.mightyoak.org.uk/tv/com7-8b.jpg
The only difference is where the frequency marker vertical bar is,
the first is C55 and the second C56. Interesting that there is
something on C57.

What's the instrument?

[Bob Latham]

Post by charles

Post by Mark Carver
Does COM 8 look the same width on screen as COM 7 (and the
other muxes) ? Bill Wright of this parish sent me a picture
that shows it looking narrower, but not as much as 1 MHz
narrower. I can't really tell on mine.

My very cheapo analyser has a normal mode which shows levels for
each channel but you can't see detail like shape or width. Here
are two pictures of the analyser in zoom mode which I suppose is
intended to show more detail but to be honest... I suppose you
get what you pay for. Mine is a hobbyists toy really.
http://www.mightyoak.org.uk/tv/com7-8a.jpg
http://www.mightyoak.org.uk/tv/com7-8b.jpg
The only difference is where the frequency marker vertical bar is,
the first is C55 and the second C56. Interesting that there is
something on C57.

What's the instrument?

Labgear S601B

https://www.labgear.co.uk/product-categories/meters-and-analysers/satellite-meters/multi-platform-meter-analyser/

Bob.

[charles]

Post by Bob Latham

Post by charles

Post by Mark Carver
Does COM 8 look the same width on screen as COM 7 (and the
other muxes) ? Bill Wright of this parish sent me a picture
that shows it looking narrower, but not as much as 1 MHz
narrower. I can't really tell on mine.

My very cheapo analyser has a normal mode which shows levels for
each channel but you can't see detail like shape or width. Here
are two pictures of the analyser in zoom mode which I suppose is
intended to show more detail but to be honest... I suppose you
get what you pay for. Mine is a hobbyists toy really.
http://www.mightyoak.org.uk/tv/com7-8a.jpg
http://www.mightyoak.org.uk/tv/com7-8b.jpg
The only difference is where the frequency marker vertical bar is,
the first is C55 and the second C56. Interesting that there is
something on C57.

What's the instrument?

Labgear S601B
https://www.labgear.co.uk/product-categories/meters-and-analysers/satellite-meters/multi-platform-meter-analyser/

Thanks

[williamwright]

Post by Bob Latham

Post by Bob Latham

Post by charles

Post by Mark Carver
Does COM 8 look the same width on screen as COM 7 (and the
other muxes) ? Bill Wright of this parish sent me a picture
that shows it looking narrower, but not as much as 1 MHz
narrower. I can't really tell on mine.

My very cheapo analyser has a normal mode which shows levels for
each channel but you can't see detail like shape or width. Here
are two pictures of the analyser in zoom mode which I suppose is
intended to show more detail but to be honest... I suppose you
get what you pay for. Mine is a hobbyists toy really.
http://www.mightyoak.org.uk/tv/com7-8a.jpg
http://www.mightyoak.org.uk/tv/com7-8b.jpg
The only difference is where the frequency marker vertical bar is,
the first is C55 and the second C56. Interesting that there is
something on C57.

What's the instrument?

Labgear S601B
https://www.labgear.co.uk/product-categories/meters-and-analysers/satellite-meters/multi-platform-meter-analyser/

Thanks

Good quality pro analysers from the pre-DTVT2 era can be had for a few
hundred pounds.

https://www.ebay.co.uk/itm/Promax-Prolink-3-advanced-tv-sat-level-meter/163585873625?hash=item26167a56d9:g:ZEkAAOSwm1Vcet0r


Bill

[i***@hansonlink.co.uk]

I got two of those last year from ofcom baldock via ramco auctions...

Total came to just shy of 100 quid!

[Brian Gregory]

Post by Bob Latham

Post by Mark Carver
Does COM 8 look the same width on screen as COM 7 (and the other
muxes) ? Bill Wright of this parish sent me a picture that shows it
looking narrower, but not as much as 1 MHz narrower. I can't really
tell on mine.

My very cheapo analyser has a normal mode which shoes levels for each
channel but you can't see detail like shape or width. Here are two
pictures of the analyser in zoom mode which i suppose is intended to
show more detail but to be honest... I suppose you get what you pay
for. mine is a hobbyists toy really.
http://www.mightyoak.org.uk/tv/com7-8a.jpg
http://www.mightyoak.org.uk/tv/com7-8b.jpg
The only difference is where the frequency marker vertical bar is,
the first is C55 and the second C56. Interesting that there is
something on C57.
Bob.

Maybe this is better:
Loading Image...
Loading Image...

It does look like COM8 is only 7MHz wide, and almost looks like possibly
with weak remnants of the extra 1MHz at the top?
(But this is also from a cheapish toy and via the dodgy TV aerial
distribution system in the block of flats where I live so it could
easily just be something to do with that)

[Ian Jackson]

Post by Brian Gregory

Post by Bob Latham

Post by Mark Carver
Does COM 8 look the same width on screen as COM 7 (and the other
muxes) ? Bill Wright of this parish sent me a picture that shows it
looking narrower, but not as much as 1 MHz narrower. I can't really
tell on mine.

My very cheapo analyser has a normal mode which shoes levels for each
channel but you can't see detail like shape or width. Here are two
pictures of the analyser in zoom mode which i suppose is intended to
show more detail but to be honest... I suppose you get what you pay
for. mine is a hobbyists toy really.
http://www.mightyoak.org.uk/tv/com7-8a.jpg
http://www.mightyoak.org.uk/tv/com7-8b.jpg
The only difference is where the frequency marker vertical bar is,
the first is C55 and the second C56. Interesting that there is
something on C57.
Bob.

https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_04_48.png
https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_03_33.png
It does look like COM8 is only 7MHz wide, and almost looks like
possibly with weak remnants of the extra 1MHz at the top?
(But this is also from a cheapish toy and via the dodgy TV aerial
distribution system in the block of flats where I live so it could
easily just be something to do with that)

Could the 'remnants' be a weak 8MHz wide MUX underneath or, although the
top end cut-off does seem sharp and well-defined, intermodulation
products from the other two MUXes?

Also, if COM8 is 7MHz wide, why is it hard against MUX7? Is its centre
frequency 0.5MHz low?

[Andy Burns]

Post by Ian Jackson
if COM8 is 7MHz wide, why is it hard against MUX7? Is its centre
frequency 0.5MHz low?

I think the intention is to leave the centre frequency as though it was
8MHz, but to not use the top 1MHz so provide a guard band towards the
forthcoming 700MHz mobile bandwidth.

I don't think the clearance is finished yet (end of April?) so maybe
there's a distant transmitter still using CH56 for something other than
the COM8 SFN and it's peeping through?

[Ian Jackson]

Post by Andy Burns

Post by Ian Jackson
if COM8 is 7MHz wide, why is it hard against MUX7? Is its centre
frequency 0.5MHz low?

I think the intention is to leave the centre frequency as though it was
8MHz, but to not use the top 1MHz so provide a guard band towards the
forthcoming 700MHz mobile bandwidth.

Surely if the centre frequency was as per 8MHz, there would be a half
meg gap at the low end? But if you keep the gap between the muxes 'as
normal', yes - you should get 1MHz of dead spectrum at the top end.

Post by Andy Burns
I don't think the clearance is finished yet (end of April?) so maybe
there's a distant transmitter still using CH56 for something other than
the COM8 SFN and it's peeping through?

Yes - as the top edge of the 'extra bit' is nice and sharp, it's
probably an off-air interloper. Intermod would probably be more splodgy.

[Brian Gregory]

Post by Andy Burns

Post by Ian Jackson
if COM8 is 7MHz wide, why is it hard against MUX7? Is its centre
frequency 0.5MHz low?

I think the intention is to leave the centre frequency as though it was
8MHz, but to not use the top 1MHz so provide a guard band towards the
forthcoming 700MHz mobile bandwidth.
I don't think the clearance is finished yet (end of April?) so maybe
there's a distant transmitter still using CH56 for something other than
the COM8 SFN and it's peeping through?

I've been thinking about it and I suspect it's just the effect of the
filters in the TV aerial distribution system being set up for the
original 8Mhz wide mux.

[williamwright]

Post by Ian Jackson
Also, if COM8 is 7MHz wide, why is it hard against MUX7? Is its centre
frequency 0.5MHz low?

Well yes because the idea is to cram both muxes into 15MHz.

Bill

[NY]

Post by Brian Gregory
https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_04_48.png
https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_03_33.png
It does look like COM8 is only 7MHz wide, and almost looks like possibly
with weak remnants of the extra 1MHz at the top?
(But this is also from a cheapish toy and via the dodgy TV aerial
distribution system in the block of flats where I live so it could easily
just be something to do with that)

TV designers in the days of analogue TV would be having kittens at the
thought of trying separate two UHF channels that were one channel (8 MHz)
apart - and you've got it 4 times in the 9 multiplexes. Times have changed!

[Brian Gregory]

Post by NY
TV designers in the days of analogue TV would be having kittens at the
thought of trying separate two UHF channels that were one channel (8
MHz) apart - and you've got it 4 times in the 9 multiplexes. Times have
changed!

The lowest frequency one (centred on 602MHz) is actually an artificial
one from a "modulator" that's added in so that we can tune to channel
400 to see images from cameras near the doors on the building so we can
buzz in only people we want to see!

The local mux should be strong enough here but it seems filters in the
distribution system do not pass it through. I believe it would be
centred on 578MHz (channel 34).

Most of the narrow spikes are probably artefacts from the SDR device I'm
using to make the plots but some may be real over the air interference.

The spike at the bottom edge of COM7 does seem to be real though.
Occasionally it gets stronger and reception of COM7 is then prone to
breaking up.

[NY]

Post by Brian Gregory
The spike at the bottom edge of COM7 does seem to be real though.
Occasionally it gets stronger and reception of COM7 is then prone to
breaking up.

After my recent experience with PSB1 and COM5 which developed moderate to
severe breakup on all channels after dark, check your room lights.

I tried turning on and off all our house lights, and then waited for the
timed/light-sensitive patio lights to come on. But I'd forgotten one set of
lights: the overhead ones in my study, next door to the affected TV and PVR,
and directly under the aerial.

As soon as I turned the lights off one evening, the "quality" of the signal
(presumably related to SNR) improved dramatically. It was then a matter of
removing each LED GU10 in turn until I found the rogue one which was putting
out a lot of digital muck at around 490 MHz (harmonic of LED switching
frequency?). It looked to be a systematic fault, because both lamps of the
same type (Crompton) reduced the quality of PSB1 and COM5, though one did a
lot more than the other.

At least it turned out to be something under my control, and not some rogue
kit belonging to a neighbour.

I wonder what it would have looked like on your scanner...

[Bob Latham]

Post by Brian Gregory
https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_04_48.png
https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_03_33.png

Brilliant. I'm very jealous. What "toy" is that?


Bob.

[Brian Gregory]

Post by Bob Latham

Post by Brian Gregory
https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_04_48.png
https://www.Brian-Gregory.me.uk/GDL/spectrumspy-2020_03_10__04_03_33.png

Brilliant. I'm very jealous. What "toy" is that?

This: https://airspy.com/airspy-r2/
and SpectrumSpy software running on a PC.

[Bob Latham]

Post by Brian Gregory
This: https://airspy.com/airspy-r2/
and SpectrumSpy software running on a PC.

Thanks.

Wow. looks like roughly £210. Is it complex to set up?

Bob.

[Brian Gregory]

Post by Bob Latham

Post by Brian Gregory
This: https://airspy.com/airspy-r2/
and SpectrumSpy software running on a PC.

Thanks.
Wow. looks like roughly £210. Is it complex to set up?
Bob.

I think direct from the manufacturer is the cheapest:
https://www.itead.cc/airspy.html
and if you choose "Registered Air Mail" it's fairly unlikely you'll have
to pay import duties.

Pretty easy to use if the software to do what you want exists.
SpectrumSpy is easy, just adjust the gain until it looks like you're
seeing the cleanest spectrum.

It can get a bit fiddly if you're trying to feed the audio from receiver
software in to some decoder software to decode some kind of digital data.

This one: https://airspy.com/airspy-hf-discovery/
performs better, especially if you just want to use it as a fancy radio,
but only covers lower frequencies.

[Jeff Layman]

Post by Bob Latham
I have been receiving com7/com8 *mostly* from Sutton C for a couple
of years and apart from when I had a distribution amp failure, the
quality has been 100%.
Last week just by chance, I looked at the quality of com7 on a 10
year old Sony tv. I had a perfect picture and sound but the set said
the quality was zero. I had a quick check around our various TVs, the
old sets all gave excellent pictures but zero quality. Newer sets all
said the quality was 100%.
I grabbed my cheapo meter/analyser and shot up the loft where I can
get the feed directly from my aerial with only about 2M of cable.
COM7 CN 15% MER 19%
COM8 CN 77% MER 99%
Can't say exactly when this changed from the previous 'perfect' but
it was fine before christmas.
Is it reasonable to assume this is the SFN and another transmitter
damaging my signal?
Odd that all tvs show no sign of a problem with picture or sound and
that the new TVs tell the quality is 100%.

There seems to be something odd going on recently with COM7/8. With my
post about Rowridge and Chris's post about Waltham, and now your post
about Sutton surely it can't just be coincidence.

FWIW I'm still getting the occasional problem with COM7 despite the
change to the aerial cable and connectors.

[Brian Gaff (Sofa 2)]

Could they be piggy backing something else on the transmitters via the links
that might be seen as a problem under already dodgy conditions?
Brian
--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
***@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!

Post by Jeff Layman

Post by Bob Latham
I have been receiving com7/com8 *mostly* from Sutton C for a couple
of years and apart from when I had a distribution amp failure, the
quality has been 100%.
Last week just by chance, I looked at the quality of com7 on a 10
year old Sony tv. I had a perfect picture and sound but the set said
the quality was zero. I had a quick check around our various TVs, the
old sets all gave excellent pictures but zero quality. Newer sets all
said the quality was 100%.
I grabbed my cheapo meter/analyser and shot up the loft where I can
get the feed directly from my aerial with only about 2M of cable.
COM7 CN 15% MER 19%
COM8 CN 77% MER 99%
Can't say exactly when this changed from the previous 'perfect' but
it was fine before christmas.
Is it reasonable to assume this is the SFN and another transmitter
damaging my signal?
Odd that all tvs show no sign of a problem with picture or sound and
that the new TVs tell the quality is 100%.

There seems to be something odd going on recently with COM7/8. With my
post about Rowridge and Chris's post about Waltham, and now your post
about Sutton surely it can't just be coincidence.
FWIW I'm still getting the occasional problem with COM7 despite the change
to the aerial cable and connectors.
--
Jeff