Mailing List Archive

UK Crystal Palace OTA reception issue on CH55
I'm a long time UK MythTV user, originally recording analog TV and now
DVBT2 dfreeview, always broadcast from the Crystal Palace transmitter to
the same roof mounted aerial that was on the house when I bought it. I'm 5
miles from the transmitter, with a reasonably good line of sight.

The aerial looks like this one

https://www.toolstation.com/loft-outdoor-tv-aerial-kit/p79595?

but it's showing its 25+ years age and has a couple of bent elements which
can't help.

Nevertheless I've not had reception problems till recently when I've
started getting regular MythTV recording failures for BBC 4 HD.

BBC 4 HD is a relatively recent addition to the lineup and I think I can
see the likely issue. It's on a high-frequency low power multiplex.

Looking here:

https://ukfree.tv/transmitters/tv/Crystal_Palace

I see that BBC 4HD is on the highest frequency multiplex (CH55 746MHZ) at
43kW, whereas all the other multiplexes I record from are below 700MHz and
at 200kW.

When the Crystal Palace Transmitter went digital I think I determined my
aerial was suitable, but I'm fairly sure that at that time all multiplexes
were on channel numbers less than 40? I'm guessing that my aerial may not
be suitable for the higher frequency multiplexes that have since appeared?

So I've got two questions:

Should my aerial be suitable for 746MHz - in which case I might look at the
cabling and splitters.

Is it worth worrying about that multiplex when the above website says this
about it.

*Being removed from Freeview (for 5G use) after November 2020*

Does anyone here have any inside information about when/if that is likely
to happen? I could just remove BBC4 HD from my lineup and make do with the
SD version.
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On 11/03/2021 22:49, David Watkins wrote:
> I'm a long time UK MythTV user, originally recording analog TV and now
> DVBT2 dfreeview, always broadcast from the Crystal Palace transmitter to
> the same roof mounted aerial that was on the house when I bought it. I'm 5
> miles from the transmitter, with a reasonably good line of sight.
>
> The aerial looks like this one
>
> https://www.toolstation.com/loft-outdoor-tv-aerial-kit/p79595?
>
> but it's showing its 25+ years age and has a couple of bent elements which
> can't help.
>
> Nevertheless I've not had reception problems till recently when I've
> started getting regular MythTV recording failures for BBC 4 HD.
>
> BBC 4 HD is a relatively recent addition to the lineup and I think I can
> see the likely issue. It's on a high-frequency low power multiplex.
>
> Looking here:
>
> https://ukfree.tv/transmitters/tv/Crystal_Palace
>
> I see that BBC 4HD is on the highest frequency multiplex (CH55 746MHZ) at
> 43kW, whereas all the other multiplexes I record from are below 700MHz and
> at 200kW.
>
> When the Crystal Palace Transmitter went digital I think I determined my
> aerial was suitable, but I'm fairly sure that at that time all multiplexes
> were on channel numbers less than 40? I'm guessing that my aerial may not
> be suitable for the higher frequency multiplexes that have since appeared?
>
> So I've got two questions:
>
> Should my aerial be suitable for 746MHz - in which case I might look at the
> cabling and splitters.
>
> Is it worth worrying about that multiplex when the above website says this
> about it.
>
> *Being removed from Freeview (for 5G use) after November 2020*
>
> Does anyone here have any inside information about when/if that is likely
> to happen? I could just remove BBC4 HD from my lineup and make do with the
> SD version.
>
If your aerial is that old it likely can't handle the range of frequencies we are expected to cover
now. I recently had to replace ours (water ingress at the connecting box, filling the honeycomb
cable with water) and the new designs cover a much wider range of channels.

I have to say that within 5 miles of CP you'd probably get a signal with a wire coathanger!

Some of the top end channels - I think 60 and up - are being sold off to 5G and the existing
multiplexes crammed into the spaces below. In theory it seems to be a good idea but we all know
about the difference between theory and practice.

The fact that the multiplex is disappearing soon doesn't mean that you'll lose any channels. All it
means is that you'll have to rescan your channels to find it again. You may find, if you do it soon,
that BBC 4HD is also being transmitted on another multiplex in preparation for the move.

You'll need to rescan soon, anyway. BBC3 is returning to the airwaves and doubtless that will mean a
reshuffle.

--

Mike Perkins

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Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On Thu, 11 Mar 2021 at 23:08, Mike Perkins <mikep@randomtraveller.org.uk>
wrote:

> You'll need to rescan soon, anyway. BBC3 is returning to the airwaves and
> doubtless that will mean a
> reshuffle.
>

Ohhh, I didn't know that. That's rather excellent news. Let's just hope
the future of BBC Four also remains secure; I understand there were rumours
of its demise a little while ago...

Cheers, Ian
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On 11/03/2021 22:49, David Watkins wrote:

>
> Looking here:
>
> https://ukfree.tv/transmitters/tv/Crystal_Palace <https://ukfree.tv/transmitters/tv/Crystal_Palace>
>
> I see that BBC 4HD is on the highest frequency multiplex (CH55 746MHZ) at 43kW, whereas all the other multiplexes I record from are below 700MHz and at 200kW.
>

Word of caution; I've found that site to be very out of date ... so it's worth double checking the data with other sources.  I use the Mendip transmitter, and what is listed for that is incorrect in respect of UHF channels and Freeview channels.  Can't speak for Crystal Palace of course.


Nige.
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On Fri, 12 Mar 2021 at 09:18, Nigel Jewell <nigel.jewell@grufty.co.uk>
wrote:

> On 11/03/2021 22:49, David Watkins wrote:
>
>
> Looking here:
>
> https://ukfree.tv/transmitters/tv/Crystal_Palace
>
> I see that BBC 4HD is on the highest frequency multiplex (CH55 746MHZ) at
> 43kW, whereas all the other multiplexes I record from are below 700MHz and
> at 200kW.
>
>
> Word of caution; I've found that site to be very out of date ... so it's
> worth double checking the data with other sources. I use the Mendip
> transmitter, and what is listed for that is incorrect in respect of UHF
> channels and Freeview channels. Can't speak for Crystal Palace of course.
>
>
> Nige.
>
>
I agree that up to date information is hard to fund. The freeview website
suggests that channel 55 will be cleared from the Crystal Palace
transmitter in Q1 2018 - but it's still there at the moment.

The only info I really trust is that provided by the MythTV scan, and so
far that's seemed to agree with the ukfree.tv website whenever I've looked
(which isn't very often). I don't generally update my channels unless I
noticed that one I want isn't working, so it can take me a while to spot
any changes.

If they do clear the 700MHz band and move the freeview broadcasts to the
existing multiplexes on the lower channel numbers then that would solve my
aerial problem. It's in a very inaccessible location on the roof so
replacing it isn't easy.

I think I'm going to remove the BBC 4 HD channel from my lineup for now and
hope it moves to an multiplex that works for me soon.
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On 12/03/2021 10:42, David Watkins wrote:
>
> If they do clear the 700MHz band and move the freeview broadcasts to the
> existing multiplexes on the lower channel numbers then that would solve my
> aerial problem. It's in a very inaccessible location on the roof so
> replacing it isn't easy.
>
> I think I'm going to remove the BBC 4 HD channel from my lineup for now and
> hope it moves to an multiplex that works for me soon.
>
Note that they may not move any channel(s) to existing multiplexes, but instead start up a new
multiplex somewhere else - as well as shuffling channels between muxes.

In my case, one of the muxes is now interleaved with others from transmitters I don't want. This
makes selecting the correct ones somewhat interesting.

I'm still on V30; it is possible that the new tuner code may make this task easier, but I'm not
holding my breath.

--

Mike Perkins

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Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
David Watkins <watkinshome@gmail.com> wrote:

> The aerial looks like this one
>
> https://www.toolstation.com/loft-outdoor-tv-aerial-kit/p79595?
>
> but it's showing its 25+ years age and has a couple of bent elements which can't help.

Hmm, looks a bit like a bacofoil contract aerial !
I get my aerials from https://www.aerialsandtv.com/ - you'll find a veritable goldmine of information there, as well as a good selection of aerials to pick from.


> Should my aerial be suitable for 746MHz - in which case I might look at the cabling and splitters.

Look at your current aerial and see what colour the plastic plugs are - though that might be difficult to see after 25 years. They are colour coded to show the aerial band - if you have (e.g.) a Group A aerial then it's not going to pick much up on Ch55.

> Is it worth worrying about that multiplex when the above website says this about it.
>
> Being removed from Freeview (for 5G use) after November 2020

Well it might not have moved yet (I suspect Covid had put a massive spanner in the works of transmitter conversions), but the politics was decided a long time ago that TV was moving down the band - so it'll move sooner or later.

It's a bit of a PITA. My main transmitter is Winter Hill which still has a mux (or two, can't remember offhand) higher up the band. But I wasn't going to buy a wideband aerial - see the aerial information on the site I linked to above to see why. So for now I have a Gp A 16 element Yagi (we're a looong way from the tx) pointed at Lancaster which, while it doesn't carry two smaller mixes WH does, has everything within the reception band for a GpA aerial. At some point (when they've done shuffling muxes down the band), I'll move it to use WH.



Mike Perkins <mikep@randomtraveller.org.uk> wrote:

> In my case, one of the muxes is now interleaved with others from transmitters I don't want. This makes selecting the correct ones somewhat interesting.

Yeah, that is interesting.
Over the years I've done a fair bit of retuning stuff for friends. It used to be simple for us - either unplug the aerial until you reach into the 50s, or unplug it after it gets to the 50s, during the tune. Our main transmitters all used frequencies up into the high 50s and 60s, while the local ones were all below 50(ish).
Then I got asked to help by someone with a nice (I suspect expensive) TV (Scandinavian sounding brand, can't remember what now, could have been Loewe) and that picked up both Winter Hill and Moel-Y-Parc (North Wales) even though M-Y-P was well off axis for the aerial. That was right PITA to deal with as it meant looking at the frequency for each of the channels (it just had BBC1, BBC1, BBC2, BBC2, and so on) and deleting the unwanted ones. In hindsight, might have been easier to pop an attenuator in while tuning - but I didn't have any back then.

At least new stuff seems to prompt for which region/area you want to use when it detects two sets of muxes.

Simon

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Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On 12/03/2021 16:06, Simon Hobson wrote:
> Mike Perkins <mikep@randomtraveller.org.uk> wrote:
>
>> In my case, one of the muxes is now interleaved with others from transmitters I don't want. This makes selecting the correct ones somewhat interesting.
>
> Yeah, that is interesting.
> Over the years I've done a fair bit of retuning stuff for friends. It used to be simple for us - either unplug the aerial until you reach into the 50s, or unplug it after it gets to the 50s, during the tune. Our main transmitters all used frequencies up into the high 50s and 60s, while the local ones were all below 50(ish).
> Then I got asked to help by someone with a nice (I suspect expensive) TV (Scandinavian sounding brand, can't remember what now, could have been Loewe) and that picked up both Winter Hill and Moel-Y-Parc (North Wales) even though M-Y-P was well off axis for the aerial. That was right PITA to deal with as it meant looking at the frequency for each of the channels (it just had BBC1, BBC1, BBC2, BBC2, and so on) and deleting the unwanted ones. In hindsight, might have been easier to pop an attenuator in while tuning - but I didn't have any back then.
>
> At least new stuff seems to prompt for which region/area you want to use when it detects two sets of muxes.
>
Yep! Our most recent TV does that which is a godsend as we can pick up from three different
transmitters: Hannington (BBC South Solent, which we want), Crystal Palace (off-beam but strong
enough. London region obvs) and Oxford (Almost behind but close enough to register. Thames Valley
local news).

The Youview Set Top Box which we currently use when we're not on myth, unfortunately does not :(. It
has picked up a range of channels, some good, some terrible and I have no idea where from. The STB
is a 'black box' and gives no clues at all. (The TV tuner on its own is useless.)

--

Mike Perkins

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Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On 12/03/2021 10:42, David Watkins wrote:
>
>
> The only info I really trust is that provided by the MythTV scan, and so far that's seemed to agree with the ukfree.tv <http://ukfree.tv> website whenever I've looked (which isn't very often).


Should have said ... I do find https://www.terrestrialtv.uk/dtt.php pretty accurate.


Nige.
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On 13/03/2021 07:25, Nigel Jewell wrote:
>
> On 12/03/2021 10:42, David Watkins wrote:
>>
>>
>> The only info I really trust is that provided by the MythTV scan, and so far that's seemed to
>> agree with the ukfree.tv <http://ukfree.tv> website whenever I've looked (which isn't very often).
>
>
> Should have said ... I do find https://www.terrestrialtv.uk/dtt.php pretty accurate.
>
Interesting. It is a pity that the site is in the middle of a rewrite, though.

Information presented in a simple, usable way is always better than an overloaded, confusing webpage
that makes you work hard for what you need to know.

--

Mike Perkins

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Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
>
> I'm still on V30; it is possible that the new tuner code may make this
> task easier, but I'm not
> holding my breath.


About channel scanning and duplicate multiplexes, you might give the
current master (pre-v32) a try.
This now has an option to automatically remove duplicate multiplexes, based
on signal strength.
Also the raw data of each scan is stored in the database; this allows a
replay of a scan with different scanning options in a few seconds.
Last but maybe not least, there is a new menu to copy non-scanned data such
as icon file path and XMLTVID from the old channels into the new channels.

> At least new stuff seems to prompt for which region/area you want to use
when it detects two sets of muxes.
About regions, for satellite (FreeSat) you can now define the region id and
the bouquet id. This decides then the channel numbering.
If there exists something similar for DVB-T/T2 I could have a look at it,
but then I would need a few recent full multiplex recordings plus a pointer
to where it is described.

Klaas.
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On Sat, 13 Mar 2021 at 10:20, Klaas de Waal <klaas.de.waal@gmail.com> wrote:

> I'm still on V30; it is possible that the new tuner code may make this
>> task easier, but I'm not
>> holding my breath.
>
>
> Last but maybe not least, there is a new menu to copy non-scanned data
> such as icon file path and XMLTVID from the old channels into the new
> channels.
>
> Klaas.
>
>
That's excellent Klass, I currently do that using a couple of sql scripts
and an Excel Spreadsheet. I'll be glad to see the back of them.
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On Sat, 13 Mar 2021 11:18:33 +0100, you wrote:

>>
>> I'm still on V30; it is possible that the new tuner code may make this
>> task easier, but I'm not
>> holding my breath.
>
>
>About channel scanning and duplicate multiplexes, you might give the
>current master (pre-v32) a try.
>This now has an option to automatically remove duplicate multiplexes, based
>on signal strength.
>Also the raw data of each scan is stored in the database; this allows a
>replay of a scan with different scanning options in a few seconds.
>Last but maybe not least, there is a new menu to copy non-scanned data such
>as icon file path and XMLTVID from the old channels into the new channels.
>
>> At least new stuff seems to prompt for which region/area you want to use
>when it detects two sets of muxes.
>About regions, for satellite (FreeSat) you can now define the region id and
>the bouquet id. This decides then the channel numbering.
>If there exists something similar for DVB-T/T2 I could have a look at it,
>but then I would need a few recent full multiplex recordings plus a pointer
>to where it is described.
>
>Klaas.

I believe that here in New Zealand for DVB-T, the LCN (logical channel
number) is available as part of the MHEG5 EPG data. But so far I have
not found any free downloadable documentation on the MHEG5 data format
- you have to pay ISO/IEC or ETSI I think, so probably only $100 or
so. The NZ MHEG5 format is a slightly modified version of the UK
MHEG5 format.

For our Sky TV NZ satellite service, the OpenTV format EPG data
carries LCNs. In my version of tv_grab_dvb_plus that I modified to
handle the Sky NZ EPG, I have it put the LCN in a comment in channel
entries in the XMLTV file:

<channel id="vibe.sky.co.nz"> <!-- number="6" type="0x19" flags="0xcf"
bouquet="25280" region="0" sid="1041" -->
<display-name>Vibe</display-name>
</channel>
<channel id="uktv.sky.co.nz"> <!-- number="7" type="0x19" flags="0xef"
bouquet="25282" region="0" sid="1003" -->
<display-name>BBC UKTV</display-name>
</channel>

The "number=" field is the LCN, and I believe that when I was
modifying tv_grab_dvb_plus, I did find documentation of where the LCN
was in the EPG data, or it was obvious when I was looking at the debug
output. The full OpenTV format documentation is also only available
if you pay - you have to take up a membership of the OpenTV
organisation, so it would be very expensive. But the basic DVB-S EPG
packet formats are able to be downloaded in the DVB Bluebooks.

If I remember correctly, the EPG data uses the sid (service ID) value
to tell which channel it applies to. So to get the LCNs, you would
need to find the packet carrying the LCN and match it to the sid from
the tuning data.

Of course, the LCNs from different sources can overlap - I add 4000 to
the LCN for my Sky NZ channels so they do not clash with my Freeview
DVB-T channels.
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Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
> Of course, the LCNs from different sources can overlap - I add 4000 to
> the LCN for my Sky NZ channels so they do not clash with my Freeview
> DVB-T channels.
>
> I do like the idea of adding an offset for Logical Channel Numbers. This
can easily be implemented with an extra field in table videosource, default
value 0.
On a related note, since v31 the channel numbers are not changed anymore
with a rescan, so a manual change of a channel number needs to be done
only once.

Klaas.
Re: UK Crystal Palace OTA reception issue on CH55 [ In reply to ]
On 11/03/2021 22:49, David Watkins wrote:
> I'm a long time UK MythTV user, originally recording analog TV and now
> DVBT2 dfreeview,  always broadcast from the Crystal Palace transmitter
> to the same roof mounted aerial that was on the house when I bought it.
> I'm 5 miles from the transmitter, with a reasonably good line of sight.
>
> The aerial looks like this one
>
> https://www.toolstation.com/loft-outdoor-tv-aerial-kit/p79595
> <https://www.toolstation.com/loft-outdoor-tv-aerial-kit/p79595>?
>
> but it's showing its 25+ years age and has a couple of bent elements
> which can't help.
>
> Nevertheless I've not had reception problems till recently when I've
> started getting regular MythTV recording failures for BBC 4 HD.
>
> BBC 4 HD is a relatively recent addition to the lineup and I think I can
> see the likely issue.  It's on a high-frequency low power multiplex.
>
> Looking here:
>
> https://ukfree.tv/transmitters/tv/Crystal_Palace
> <https://ukfree.tv/transmitters/tv/Crystal_Palace>
>
> I see that BBC 4HD is on the highest frequency multiplex (CH55 746MHZ)
> at 43kW, whereas all the other multiplexes I record from are below
> 700MHz and at 200kW.
>

The fundamental problem is that Crystal Palace was originally a Group A
transmitter, which is essentially the lower half of the channel space
and therefore people had aerials installed for Group A.

Now with the move up to ch55, this is outside Group A, and therefore a
different group aerial is required to receive it (this is especially
true if you are further away, like me)

Apparently it is supposed to move back down to the group a freq range,
but I can never find out if that is actually still planned to happen,
or if they have just given up.


Regards
Stuart

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